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Air ions and mood outcomes: A review and meta-analysis

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Air ions and mood outcomes: A review and meta-analysis

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Psychological effects of air ions have been reported for more than 80 years in the media and scientific literature. This study summarizes a qualitative literature review and quantitative meta-analysis, where applicable, that examines the potential effects of exposure to negative and positive air ions on psychological measures of mood and emotional state. A structured literature review was conducted to identify human experimental studies published through August, 2012. Thirty-three studies (1957–2012) evaluating the effects of air ionization on depression, anxiety, mood states, and subjective feelings of mental well-being in humans were included. Five studies on negative ionization and depression (measured using a structured interview guide) were evaluated by level of exposure intensity (high vs. low) using meta-analysis. Consistent ionization effects were not observed for anxiety, mood, relaxation/sleep, and personal comfort. In contrast, meta-analysis results showed that negative ionization, overall, was significantly associated with lower depression ratings, with a stronger association observed at high levels of negative ion exposure (mean summary effect and 95% confidence interval (CI) following high- and low-density exposure: 14.28 (95% CI: 12.93-15.62) and 7.23 (95% CI: 2.62-11.83), respectively). The response to high-density ionization was observed in patients with seasonal or chronic depression, but an effect of low-density ionization was observed only in patients with seasonal depression. However, no relationship between the duration or frequency of ionization treatment on depression ratings was evident. No consistent influence of positive or negative air ionization on anxiety, mood, relaxation, sleep, and personal comfort measures was observed. Negative air ionization was associated with lower depression scores particularly at the highest exposure level. Future research is needed to evaluate the biological plausibility of this association.
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RES E AR C H A R T I C L E Open Access
Air ions and mood outcomes: a review and
meta-analysis
Vanessa Perez
1
, Dominik D Alexander
2
and William H Bailey
3*
Abstract
Background: Psychological effects of air ions have been reported for more than 80 years in the media and
scientific literature. This study summarizes a qualitative literature review and quantitative meta-analysis, where
applicable, that examines the potential effects of exposure to negative and positive air ions on psychological
measures of mood and emotional state.
Methods: A structured literature review was conducted to identify human experimental studies published through
August, 2012. Thirty-three studies (19572012) evaluating the effects of air ionization on depression, anxiety, mood
states, and subjective feelings of mental well-being in humans were included. Five studies on negative ionization
and depressi on (measured using a structured interview guide) were evaluated by level of exposure intensity (high
vs. low) using meta-analysis.
Results: Consistent ionization effects were not observed for anxiety, mood, relaxation/sleep, and personal comfort.
In contrast, meta-analysis results showed that negative ionization, overall, was significantly associated with lower
depression ratings, with a stronger association observed at high levels of negative ion exposure (mean summary
effect and 95% confidence interval (CI) following high- and low-density exposure: 14.28 (95% CI: 12.93-15.62) and
7.23 (95% CI: 2.62-11.83), respectively). The response to high-density ionization was observed in patients with
seasonal or chronic depression, but an effect of low-density ionization was observed only in patients with seasonal
depression. However, no relationship between the duration or frequency of ionization treatment on depression
ratings was evident.
Conclusions: No consistent influence of positive or negative air ionization on anxiety, mood, relaxation, sleep, and
personal comfort measures was observed. Negative air ionization was associated with lower depression scores
particularly at the highest exposure level. Future research is needed to evaluate the biological plausibility of this
association.
Keywords: Mood disorders, Depression, Air ionization, Ion exposure, Epidemiology, Systematic review, Negative ion,
Positive ion
Background
Several experimental human studies on air ion exposure
and mood ratings have been published throughout the
years. While their evidence is inconsiste nt, the findings
have increased awareness of mood alterations possibly
associated with such exposure. Ions are ubiquitous,
whereby any molecule with an unbalanced electron to
proton ratio results in a net positive or negative elec-
trical charge [1]. Air ions are produced from alterations
in the atmosphere and weather phenomena, by natural
radioactivity, and by combustion processes [2,3]. They
are also generated by air ionizers sold commercially and
by corona activity on the surface of high voltage conduc-
tors of transmission lines.
Some experimental research indicates that exposure to
negative air ions is linked to reduced depression severity
[4-8], lower psychological stress [9], less anxiety [10],
and enhanced well-being [11-14]. Others suggest that
exposure to positive air ions may be associated with
feelings of unpleasantness, irritability, and heightened
* Correspondence: wbailey@exponent.com
3
Exponent, Inc., Health Sciences, Center for Exposure Assessment and Dose
Reconstruction, 17000 Science Drive, Suite 200, Bowie, MD 20715, USA
Full list of author information is available at the end of the article
© 2013 Perez et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.
Perez et al. BMC Psychiatry 2013, 13:29
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anxiety [15-17]; while some have found no mood altera-
tions associated with air ionization [18,19].
Historically, evidence of psychological measures and
air ionization has been equivocal because research find-
ings use heterog eneous experimental protocols evaluat-
ing diverse study populations; use various methods to
measure mood-related outcomes; and use inadequate ex-
perimental design and procedures including control over
relevant exposures [20]. Diagnostic trends for classifying
mood disorders and technological advancements in
environmental therapies (e.g. air ionization systems)
have likely influenced study findings. Furthermore, most
studies have tested relatively small study populations. To
the best of our knowledge, no current review has sum-
marized the possible effects on mood and well-being
attributed to air ionization. We therefore conducted a
structured literature review to evaluate human experi-
mental studies on positive and negative air ion exposure
and ratings of depression, anxiety, mood states, and
subjective feelings of mental well-being. In addition, we
quantitatively examined negative air ionization and
depression symptom se verity using meta-analysis.
Methods
Literature search and study identification
A structured literature review performed for the Minnesota
Environmental Quality Board on the biological/heal th
effects attributed to air ions and direct current transmission
lines was used to identify the historical literature up to
1982 [21]. We further conducted a structured literature
search using Medline (PubMed) to identify experimental
studies published between 1 January 1982 and August,
2012 on air ionization and depression, anxiety, mood states,
and subjective feelings of mental well-being in humans.
ProQuest DIALOG was used to retrieve studies from the
environmental and behavioral sciences, engineering, and
other technical databases, including Elsevier, Biobase, and
Embase.
Identical search strings for PubMed and ProQuest
DIALOG referenced the exposure (air ions, charged
aerosols, corona ions, atmos pheric ions, ionization,
ionized air, heavy ions, light ions) and outcomes of interest
(depression, anxiety, mood, activation, personal comfort, re-
laxation, sleepiness). We manually reviewed reference lists
in all retrieved articl es for rela ted public ations . Thi rty-t hree
English-language studies published between 1957 and 2012
metourinclusioncriteria(Table1).
Inclusion criteria consisted of experiments among
subjects exposed to negatively- or positively-charged
small air ions, or both; studies published in the English
language; and studies that reported associations between
ionization and mood indicators (e.g., depression, anxiety,
mood states, and reports of mental well-being). No
restrictions on the number of subjects evaluated in each
study were required. Animal studies, letters to the editor
and editorials , references not reporting original data,
and studies with no relevant exposure or outcome were
excluded.
Data extraction and statistical methods
Qualitative information (study population/design, ion
polarity/concentration, exposure duration) and quantita-
tive data (mood indicator effects) were extracted. Studies
were consolidated qualitatively into four outcome cat-
egories: activation, anxiety, and mood; relaxation/sleep;
personal comfort ratings; and depression.
A meta-analysis was performed on five studies [4,6-8,22]
of negative air ionization and depression symptom severity
as measured using the 29-item Structured Interview Guide
for the Hamilton Depression Rating Scale, Seasonal
Affective Disorders (SIGH-SAD), which consists of the
21-item Hamilton Depression Rating Scale and the 8-item
Atypical Scale. Forest plots from random effects modeling
[23] were generated to estimate weighted group mean
differences in depression scores, 95% confidence intervals
(CIs), and corresponding p-values for heterogeneity. Of
note, using the random effects analysis, the weighted
mean is defined as the sum of each study effect size multi-
plied by its weight (i.e., the inverse of the within-study
variance plus the between-studies variance) divided by the
sum of the weights. The variance of the weighted group
mean difference is defined as the reciprocal of the sum of
the weights. The data from Terman and Terman [6] were
extracted from their Figure one; exact values have been
requested from the authors. Depression score data before
and after exposure to low density ions were also requested
from Dauphinais et al. [24] for possible inclusion. Sensitiv-
ity analyses were performed to examine data robustness.
Publication bias was assessed using funnel plots, the Begg
rank correlation test, and Eggers regression analysis. All
analyses were performed using the Comprehensive Meta-
Analysis software (version 2.2.046; Biostat, Englewood,
NJ). Additional doseresponse relationships were evalu-
ated by plotting exposure duration by depression score
mean differences and their corresponding 95% CIs in
Microsoft Excel (2010).
Results
Studies meeting inclusion criteria are summarized in
Table 1. All studies included adults only and sample
sizes ranged from 4 to 124 participants. Apart from the
studies that evaluated ion effects on patients with some
form of depression, six studies [11,14,19,25-27] also e val-
uated the influence of ions on mood states of persons
with varying health conditions. Collectively, the findings
from these six studies did not provide contrasting results
from those studies that included only healthy subjects.
Most studies examined negative air ionization only
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Table 1 Study characteristics
Author and year Study objective Study design Blinding Study population Total sample size
Silverman and
Kornblueh 1957[27]
a,b
Evaluate effect of negative and positive ions on
the human electroencephalogram and sleep
Crossover experiment Not reported 10 healthy adults and 2 additional subjects with
chronic stationary neurologic conditions
12
McGurk, 1959[17]
c
Evaluate effect of negative and positive ions on
self-reported feelings of comfort
Crossover experiment Single-blind (subjects) 10 college-aged males 10
Yaglou, 1961[19]
b
Evaluate effect of negative and positive ions on
relaxation
Crossover experiment Single-blind (subjects) 25 healthy adults (age range: 2251) 25
Yaglou, 1961[19]
b
Evaluate effect of negative and positive ions on
relaxation and sleepiness
Crossover experiment Single-blind (subjects) 6 arthritic patients (age range: 3062) 6
Assael et al., 1974[11]
b
Evaluate effect of negative ions on human
electroencephalogram
Crossover experiment Double-blind 10 healthy participants (age range: 2065) and
10 subjects receiving tranquilizers
20
Albrechtsen et al.,
1978[37]
b,c
Evaluate effect of negative and positive ions on
human well-being and mental performance
Crossover experiment Single-blind (subjects) Study 1: six women (age range: 2030) chosen
at random; study 2: 12 subjects (age range: 19
45) selected because they appeared to be most
sensitive to ionization
Study 1: 6 Study 2:
12
Charry and
Hawkinshire, 1981[15]
a
Evaluate effect of negative and positive ions on
mood
Crossover experiment Single-blind (subjects) 85 adults (age range: 1860; mean age: 30) 85
Hawkins, 1981[38]
b, c
Evaluate effect of negative and positive ions on
subjective well-being and comfort
Crossover experiment Double-blind Study groups based on three areas of variable
air ionization levels within the building (area 1:
20 women; area 2: 32 adults; and area 3: 54
adults)
Area 1: 20
Area 2: 22
Area 3: 54
Tom et al., 1981[34]
a,b
Evaluate effect of negative ions on human
performance and mood
Randomized controlled
trial
Double-blind 56 adults (age range: 1761; mean age: 23) 56
Buckalew and Rizzuto,
1982[12]
a,b
Evaluate effect of negative ions on subjective
feelings of mood and psychological state
Randomized controlled
trial
Double-blind Two groups of 12 paid male volunteers
matched on age, education, physical condition,
and smoking habits (age range: 2030; mean
age: 22.8)
24
Dantzler et al.,
1983[25]
a
Evaluate effect of positive and negative ions on
somatic symptoms and mood changes
Crossover experiment Double-blind 9 patients with bronchial asthma (age range:
3564)
9
Baron et al., 1985[28]
a
Evaluate effect of negative ions on self-reported
affect/mood
Crossover experiment Single-blind (subjects) 71 male undergraduate students 71
Deleanu and
Stamatiu, 1985[29]
a,b,d
Evaluate effect of negative ions on psychiatric
symptoms
Experimental (no control
group)
Not reported 112 patients with neurasthenias, psychoses, or
personality disorders
112
Gianinni et al.,
1986[16]
a
Evaluate effect of negative and positive ions on
anxiety, excitement, and suspicion
Crossover experiment Double-blind 14 university-affiliated volunteers 14
Gianinni et al., 1986/
1987[30]
a
Evaluate effect of positive ions on anxiety and
excitement
Crossover experiment Double-blind 12 adult male volunteers 12
Finnegan et al., 1987
[40]
c
Evaluate effect of negative ions on personal
comfort rating
Crossover experiment Single-blind (subjects) 26 adults working within 5 different rooms of
an office building
26
Hedge and Collis,
1987[18]
a
Evaluate effect of negative ions on mood Crossover experiment Double-blind 28 healthy women (age range: 1958) 28
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Table 1 Study characteristics (Continued)
Lips et al., 1987[13]
b,c
Evaluate effect of negative ions on well-being
and comfort
Crossover experiment Double-blind 18 normal, healthy employees working in one
of two rooms, whereby room 1 had windows
providing air ventilation and room 2 was
mechanically ventilated
18
Misiaszek et al.,
1987[14]
a,b
Evaluate effect of negative ions on manic
behavior and sleep
Experimental (phase I: no
control group; phase II:
with-in subjects, repeated
measures)
Phase I: No Blinding
Phase II: Double-blind
8 manic patients (age range: 2249) Phase I: 4 Phase II: 4
Reilly and Stevenson,
1993[33]
a
Evaluate effect of negative ions on anxiety Crossover experiment Single-blind (subjects) 8 healthy men (age range: 1925) 8
Terman and Terman,
1995[6]
d
Evaluate effect of negative ions on seasonal
depression
Randomized controlled
trial
Double-blind 25 patients (mean age: 38.2 ± 11) with winter
depression
Low-density negative
ion group: 13 High-
density negative ion
group: 12
Watanabe et al.,
1997[35]
a,c
Evaluate effect of negative ions on mood and
pleasantness
Crossover experiment Single-blind (subjects) 13 healthy adults (age range: 2149; mean
age: 26.4)
13
Terman et al.,
1998[8]
b,d
Evaluate effect of negative ions on sleep and
seasonal depression
Crossover experiment Double-blind 124 subjects (age range: 1859; mean age: 39.4
± 9.8) with seasonal affective disorder
124 (20 randomized
to high-density
negative ionization
and 19 randomized
to low-density
negative ionization)
Nakane et al., 2002[10]
a
Evaluate effect of negative ions on anxiety Crossover experiment Not reported 12 female undergraduates (age range: 1822) 12
Iwama et al., 2004[39]
b
Evaluate effect of negative ions on tension Randomized controlled
trial
Double-blind 44 patients randomized to the control and 51
patients randomized to receive treatment
(mean age among men: 37 ± 18; mean age
among women: 43 ± 20)
95
Goel et al., 2005[22]
b,d
Evaluate effect of negative ions on sleep and
chronic depression
Randomized controlled
trial
Double-blind 32 patients (age range: 2265; mean age: 43.7 ±
12.4) with non-seasonal chronic depression
32 (22 randomized to
low- or high-density)
Goel and Etwaroo,
2006[5]
a,b,d
Evaluate effect of negative ions on depression,
total mood disturbance, and anger
Randomized controlled
trial
Single-blind (subjects) 118 mildly depressed and non-depressed
college students (mean age: 19.4 ± 1.7)
118 (59 randomized
to low or high
density)
Terman and Terman,
2006[7]
b,d
Evaluate effect of negative ions on sleep and
seasonal depression
Randomized controlled
trial
Double-blind 99 adults with seasonal depression (94 cases)
and bipolar II disorder (five cases) (age range:
1963; mean age: 40.4 ± 10.4)
99 (39 randomized to
low or high density)
Gianinni et al.,
2007[26]
a
Evaluate effect of negative ions on manic states Crossover experiment Double-blind 24 manic male patients (age range: 2329;
mean age: 26.7)
24 (20 analyzed)
Malcolm et al.,
2009[32]
a,b
Evaluate effect of negative ions on positive
affective memory
Randomized controlled
trial
Single-blind (subjects) 30 healthy subjects (age range: 1828)
randomized to either receive high-density
negative air ion exposure or to a control
condition
30
Flory et al., 2010[4]
d
Evaluate effect of negative ions on seasonal
depression
Randomized controlled
trial
Single-blind (subjects) 73 university-affiliated women (age range:
1851; mean age: 20.8 ± 5.69) with seasonal
affective disorder
73 (38 randomized to
low or high density)
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Table 1 Study characteristics (Continued)
Malik et al., 2010[9]
a
Evaluate effect of negative ions on
psychological stress
Crossover experiment Single-blind (subjects) 20 regular users of computers as part of their
job (age range: 2435; mean age: 28.9)
20
Dauphinais et al.,
2012[24]
d
Evaluate the effect of negative air ions on
seasonal depression
Randomized controlled
trial
Double-blind 44 adult patients (20 in the low-density group)
with bipolar depression
20
Harmer et al., 2012[31]
a,b,d
Evaluate the effect of high-density negative air
ions on emotional processing in patients with
seasonal depression
Randomized controlled
trial
Double-blind 21 adult patients with seasonal depression;
21 controls. Mean ages of groups between
3035 years
42
a
Activation, anxiety, mood.
b
Relaxation and sleep.
c
Personal comfort rating.
d
Depression.
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(n=24); one examined positive air ionization only; and
eight studied the effects of both. Blinding of study
subjects was not reported in three experiments, nor was
it obvious upon review of the study methodology.
Among the 30 studies that conducted blind experiments,
18 were double-blind. All but one study [19] was
published in a peer-reviewed journal.
Air ion intensities and duration are summarized in
Table 2. Air ion intensities were reported in 29 studies
(range: 1000 ions/cm
3
(ambient levels) to 27,500,000
ions/cm
3
). Air ionization duration ranged from 10 minutes
atasingletimepoint,todailytreatment periods adminis-
tered for multiple days, to successive weeks at a time where
air ion generators were switched on continuously. Collect-
ively, many studies reported a mood-related response
after exposure t o ionized air; howe ver, considerable
variation by outcome, statistical significance testing, and
degree of precision across the reported data was not ed.
For reporting purposes, we have organized our review
of studies by outcome, ascending year of publication,
and the first authors last name.
Activation, anxiety, and mood outcomes
Four studies examined the effects of negative and positive
air ions on activation, anxiety, and mood [15,16,25,27].
Silverman and Kornbleuh [27] conducted an experiment
to examine the effect of negative and positive air
ionization on the human electroencephalogram (blinding
not reported). Ten healthy adults and two subjects with
chronic stationary neurologic conditions participated in
the study. Findings indicated a consistent decrease in
alpha activity, a non-specific response, ranging from 0.5 to
1.5 cycle decrements during negative or positive air
ionization, or both, in 10 subjects (9 healthy; 1 neurologic-
ally impaired).
Charry and Hawkinshire [15] examined the effect of posi-
tiveairionsonmoodin85subjects(agerange:1860;
mean age: 30) in contrast to ambient conditions in a single-
blind experiment and found significantly greater tension
and irritability in subjects mood states. In particular,
ion-sensitive subjects showed that activation decreased
and reaction times increased during exposure to positive
air ions while non-sensitive subjects showed increased acti-
vation and n o effects on reaction time.
Dantzler et al. [25] reported that ratings of mood on
three questionnaires by nine subjects with bronchial
asthma (age range: 3564) were unaffected by exposure
to negative and positive ions for 6-hour exposure
periods in a double-blind crossover study. In contrast,
Gianinni et al. [16] used a double-blind crossover design
to evaluate the influence of negative and positive air ions
in 14 university-affiliated volunteers and found that
positive air ionization significantly increased anxiety,
excitement, and suspicion. In contrast, negative air
ionization significantly lowered subjects extent of suspi-
cion and excitement to those levels attained prior to
positive air ion exposure.
Fifteen studies on activation, anxiety, and mood
examined the effect s of negative air ions only
[5,9,10,12,14,18,26,28-35]. Tom et al. [34] utilized a
dou b l e -b l i n d randomiz ed controlled study to determine
the impact of negative air ions on mood in 56 adults
(age range : 1761; mean age: 23). No significant d iffer-
ences were observed between experimental and control
conditions. On the other hand, Buckalew and Rizzuto
[12] conducted a double-blind randomized controlled
trial (RCT) and identified a significant improvement in
mood attributed to negative air ionization between
experimental (n=12 men) and control (n=12 men)
groups (age range: 2030; mean age: 22.8).
Baron et al. [28] examined the effect of negative air
ionization on mood, memory, and aggression as mediated
by personality type among 71 male undergraduate stu-
dents in a single-blind experiment. The authors found that
exposure to moderate/high concentrations of negative air
ions significantly heightened aggression among subjects
classified as Type A, but not Type B. In addition, the
authors reported that negative air ionization produced
positive shifts in mood when not provoked by an accom-
plice, but negative shifts in mood when incited.
Deleanu and Stamatiu [29] conducted an experiment of
112 patients with mental disorders (blinding not
reported). The overall study goal was to mitigate patients
symptoms by exposing them to negative aeroionotherapy
for 10 to 30 days. The findings suggested that in the ma-
jority of treated patients, attenuation or the complete dis-
appearance of anxiety and depressive reactions, including
insomnia and general disposition, were identified. In con-
trast, Hedge and Collis [18] examined the impact of nega-
tive air ionization on mood in a double-blind study
conducted among 28 healthy women and found no signifi-
cant benefit of exposure.
Misiaszek et al. [14] explored the influence of negative
air ions on eight manic patients (age range: 2249) in an
experimental pilot study conducted in two phases of
four subjects each. The first phase was non-blind and
the second was double-blind involving collection of data
using anxiety and psychiatric metrics. In phase two,
three of the four subjects showed score redu ctions con-
sistent with clinica l improvement; however, inference of
these findings was impossible due to the limited number
of subject s examined. A more recent single-blind experi-
ment by Reilly and Stevenson [33] evaluated anxiety
levels among eight healthy men (age range: 1925) who
were exposed to negative air ionization. The results
showed no significant effect of air ions on state anxiety
pre- or post-exercise [33]. In a single-blind study con-
ducted by Watanabe et al. [35], 13 healthy adults (age
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Table 2 Air ion exposure assessment, psychological measures, and study findings
Author and year Air ion exposure (Duration) Ion concentration Metrics used for mental health outcomes Primary findings
Silverman and
Kornblueh 1957[27]
a,b
Negative air ion (30 minutes) Not reported Human electroencephalogram Decrease in alpha frequency in most subjects; half of the
subjects reported relaxation and sleepiness with ionization
(slightly more frequent for () than (+) ion exposure); one
consistent finding was a decrease in alpha frequency
during negative or positive ionization (or both) in all but
two subjects. Findings reported as transient.
Positive air ion (30 minutes) Activations by hyperventilation, apnea, photic stimulation
and sleep (natural)
McGurk, 1959[17]
c
Negative air ion (5 hours) 8.0 × 10
3
ions/cm
3
Self-reported feelings of comfort, ease by which subjects
worked on a cognitive task, and reactions to the test room
atmosphere
Regarding negative ionization, a significant percent of
subjects appeared to detect ionization condition despite
blinding and reported more pleasant feelings.
Positive air ion (2 hours) Regarding positive ionization, subjects reported more
unpleasant feelings.
Yaglou, 1961[19]
b
Negative air ion (12 hours) 5,000 to 10,000
ions/cm
3
air
Self-reported impressions (indifference, relaxation, air
freshness, headache, respiratory irritation, restlessness)
Subjectively, positive air ions seemed to increase the
incidence of upper respiratory irritation in the winter,
while negative air ions had little or no effect on the
quality of air.
Positive air ion (12 hours) 5% of subjects reported feeling relaxed when exposed to
positive air ions; 17% reported feeling relaxed when
exposed to negative air ions; and 21% of subjects
reported feeling relaxed under control conditions
Yaglou, 1961[19]
b
Negative air ion (12 hours) 10
5
-10
6
ions/cm
3
air Self-reported impressions (indifference, relaxation, air
freshness, headache, respiratory irritation, restlessness)
Subjectively, negative air ions did not alleviate joint
symptoms, while positive air ions seemed to make the
symptoms worse; a higher frequency of patients reported
feeling relaxed or sleepy, or both when exposed to
negative versus positive air ions
Positive air ion (12 hours)
Assael et al., 1974[11]
b
Negative air ion (45 minutes) 3.5 × 10
5
ions/cm
3
EEG parameters: Decrease in alpha frequency manifestation of general
relaxation induced by negative air ions. Increase of
amplitude interpreted as improvement of perception and
apperception. Subjectively, all patients experienced initial
relaxation followed by alertness connected with moving
of alpha-waves from occipital to frontal areas.
frequency (Hz)
amplitude (μV)
spreading of alpha waves area
synchronization of right and left hemispheres
Self-reported relaxation, alertness, working capacity, relief
Albrechtsen et al.,
1978[37]
b,c
Negative air ion (Experiment
I: 8 hours; Experiment II: 15
minutes) Positive air ion
(Experiment I: 8 hours;
Experiment II: 15 minutes)
300-9,000 ions/cm
3
Mental performance: No significant effects of positive or negative air ions
found.
number of tasks per hour
Subjective voting based on % scale:
extent of exertion
perception on air quality
perception of tasks
current feeling (sleepy vs. alert)
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Table 2 Air ion exposure assessment, psychological measures, and study findings (Continued)
Charry and
Hawkinshire, 1981[15]
a
Positive air ion (1.5 hours ) Positive air ions: 2.0-
3.0 × 10
4
ions/cm
3
Mood Adjective Check List For most subjects, mood changes induced by air ion
exposure characterized by increased tension and
irritability.
Ambient condition
(contained both) (1.5 hours)
Ambient:
3.0 × 10
2
ions/cm
3
Sharav Questionnaire (mood)
Hawkins, 1981[38]
b, c
Negative air ion (Weeks 5 to
12- on continuously)
Negative air ion:
2.0-3.5 × 10
3
ions/cm
3
Personal ratings of thermal comfort, stuffiness, alertness,
well-being
Negative air ion exposure associated with higher
subjective ratings of alertness, atmospheric freshness,
environmental/personal warmth, and a reduction in the
overall complaint rate by 50%. Night-shift working was
associated with discomfort and ill-health. Positive air ion
effects were not explicitly discussed.
Positive air ion (Weeks 5 to
12- on continuously)
Positive air ion: 50
125 ions/cm
3
air
Tom et al., 1981[34]
a,b
Negative air ion (15 minutes) Negative air ion:
16,160 ions/cm
3
Likert scale survey for psychological state (difficulty of
concentration, energetic, mood state, sociable, relaxed)
Subjects reported being more energetic and finding it
easier to concentrate under the experimental condition
than the control condition. Negative air ion exposure had
a positive effect on certain aspects of human performance
and mood.
Control (natural
environment):
204.4 ions/cm
3
Buckalew and Rizzuto,
1982[12]
a,b
Negative air ion (6 hours) Not reported Taylor Manifest Anxiety Scale (TMAS) Mood index data showed significant changes in the
subjective perception of both physiological state
(relaxation increased) and psychological state (irritability,
depression, and tenseness decreased while calmness and
stimulation increased).
Self-report Mood Index
Dantzler et al.,
1983[25]
a
Negative air ion (6 hours) Negative and positive
air ions: 60,000-
110,000 ions/cm
3
Sharav Questionnaires 1 and 2 Mood Adjective Check List Patients mood did not differ significantly between the
two ion exposures.
Positive air ion (6 hours)
Baron et al., 1985[28]
a
Negative air ion (20 minutes) Ambient condition:
2.0-3.0 × 10
2
ions/cm
3
Self-reported affect (Profile of Mood States survey) Exposure to moderate or high levels of negative air ions
significantly enhanced aggression by Type A subjects, but
not among others. Negative air ions produced positive
shifts in reported moods in the absence of provocation,
but negative shifts in moods in the presence of
provocation.
Moderate condition:
4×10
4
ions/cm
3
Aggression measured by mean level of heat selected by
subjects on each of the 20 occasions when the red light
appeared
High condition:
7.0-8.0 × 10
4
ions/cm
3
Memory measured by the number of traits and the
number of behaviors subjects could recall about the
accomplice
Deleanu and
Stamatiu, 1985[29]
a,b,d
Negative aeroionotherapy
(daily treatment of 1550
minutes for 1030 days)
1-1.5 × 10
4
ions/cm
3
Amelioration of asthenia, depressive reactions, anxiety,
excitability and irascibility, cephalea, insomnia, and general
disposition in patients with various psychiatric disorders
In most treated patients, a diminution or even the
disappearance of the target symptoms was obtained
(asthenia, depressive reactions, anxiety, irascibility,
cephalea, insomnia, and general disposition).
Gianinni et al.,
1986[16]
a
Negative air ion (20 minutes) Negative air ion: not
reported
Brief Psychiatric Rating Scale Cations were found to increase anxiety, excitement, and
suspicion. Anions reversed the effects of cations and, in
addition, reduced suspicion and excitement to levels
below those occurring before cationization.
Positive air ion (20 minutes)
Positive air ion:
2.9 × 10
3
ions/cm
3
Gianinni et al.,
1986/87[30]
a
Positive air ion (2 hours) 2,050-2,300 ions/cm
3
Brief Psychiatric Rating Scale Symptoms of anxiety and excitement significantly
increased. During the time of exposure, serum serotonin
levels also increased significantly.
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Table 2 Air ion exposure assessment, psychological measures, and study findings (Continued)
Finnegan et al.,
1987[40]
c
Negative air ion (68 weeks) 1.84 × 10
3
ions/cm
3
Personal comfort rating No significant effect on personal comfort found. Effects
on symptoms were non-significant except for URTI and
nausea in the high negative air ion period.
Hedge and Collis,
1987[18]
a
Negative air ion (7 hours) 2 × 10
4
ions/cm
3
Mood Adjective Check List Evidence for beneficial effects of negative air ions on
mood and performance could not be demonstrated.
Two cognitive tasks:
naming 24 different colors printed on card
Stroop Colour Word test
Lips et al., 1987[13]
b,c
Negative air ion Weeks 2 and
4 - on continuously; Week 3 -
mornings only
5×10
4
ions/cm
3
10 linear scales (rated 0 to 10) on which each subject was
asked to assess his or her well-being and the quality of the
environment
After their exposure to enhanced negative air-ion
concentrations, the subjects' assessments of both their
own well-being and the quality of the environment
improved significantly: neither harmful effects of exposure
to enhanced levels of negative air ions nor changes in
perceived thermal comfort were detected.
Misiaszek et al.,
1987[14]
a,b
Negative air ion Phase I: 1
hour; Phase II: 1.5 hours
Phase I: 40,000-60,000
small,
501000 medium,
504,000 large ions/
cm
3
State Trait Anxiety Inventory and Inpatient
Multidimensional Psychiatric Scale
Phase I: All subjects fell to sleep, reported being calm
afterwards; manic behavior reappeared 510 minutes after
treatment
Phase II: 3/4 subjects fell to sleep, 1 subject appeared less
agitated; manic behavior reappeared 510 minutes after
treatmentPhase II: 50,000-70,000
small,
503,200 medium,
507,000 large ions/
cm
3
Reilly and Stevenson,
1993[33]
a
Negative air ion (30 minutes
pre-test + 40 minutes during
test)
1.72 × 10
5
ions/cm
3
Measurements were made of state anxiety according to
Spielberger et al. (1970)
There was no significant effect of air ions on state anxiety
pre-or post-exercise or on the perception of effort.
Terman and Terman,
1995[6]
d
Negative air ion (30 minute
sessions for 20 days)
Low density:
1.0 × 10
4
ions/cm
3
SIGH SAD The severity of depressive symptoms decreased selectively
for the group receiving high-density treatment. When a
remission criterion of 50% or greater reduction in
symptom frequency/severity was used, 58% of subjects
responded to high-density treatment while 15%
responded to low-density treatment.
Clinical Global Impressions Scale
High density:
2.7 × 10
6
ions/cm
3
Watanabe et al.,
1997[35]
a,c
Negative air ion (10 minutes) 2.0 × 10
4
ions/cm
3
Self-reported feelings of temperature, pleasantness, fatigue,
and sweating
There were no differences in the moods of these persons
or changes in their blood pressures between the two
saunas.
Terman et al.,
1998[8]
b,d
Negative air ion (30 minutes
per day for 1014 days)
Low density:
1.0 × 10
4
ions/
cm
3
High density:
2.7 × 10
6
ions/cm
3
SIGH SADSelf-rating version of the SIGH-SADSleep
patterns
Improved depression rating of 42-50% and 20-40%
remission rate. Described as a "small effect" in period 1
and "large effect" in period 2. Analysis of depression scale
percentage change scores showed low-density air ion
response to be inferior to all other groups, with no other
group differences. Sleep measures subjects given morning
light awakened 0.62 ± 0.62 hours earlier than at baseline;
negative air ions, 0.41 ± 0.37 hours earlier; and evening
light, 0.09 ± 0.58 hours earlier.
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Table 2 Air ion exposure assessment, psychological measures, and study findings (Continued)
Nakane et al.,
2002[10]
a
Negative air ion (40 minutes
during task or 30 minutes
post-task)
5.5-7.3 × 10
3
ions/cm
3
Japanese version of the State-Trait Anxiety Inventory,
Anxiety StateSalivary cortisol and chromogranin A-like
immunoreactivityTask performance
The increase in the CgA-like IR level was attenuated by
the exposure to negative air ions during the task. The
exposure to air ions during the recovery period following
the task was effective for rapidly decreasing the CgA-like
IR level that had increased after the task. These effects by
negative air ions were also observed using STAI-S. Task
performance was slightly but significantly improved by
the presence of negative air ions.
Iwama et al.,
2004a[39]
b
Negative ion (not reported) 3000 parts/cm
3f
Degree of tension: 1 = relaxed; 2 = normal tension;
3 = mild tension; 4 = moderate tension; and
5 = severe tension
Degree of tension decreased significantly and more
rapidly in the negative ion-rich environment.
Goel et al., 2005[22]
b,d
Negative ion (1 hour upon
wakening for 5 weeks)
Low density:
1.7 × 10
11
ions/s
[1 × 10
4
ions/cm
3
]
e
SIGH SAD SIGH-SAD score improvement was 51.1% for high-density
ions v. 17.0% for low-density ions. Remission rates were
50% and 0%, respectively.
High density:
4.5 × 10
14
ions/s
[2.7 × 10
7
ions/cm
3
]
e
Evening saliva samples obtained before and after treatment
for ascertainment of circadian melatonin rhythm phase
Goel and Etwaroo,
2006[5]
a,b,d
Negative ion (30 minutes for
three consecutive evenings)
Low density:
1.7 × 10
11
ions/s
[1 × 10
4
ions/cm
3
]
e
High density:
4.5 × 10
14
ions/s
[2.7 × 10
7
ions/cm
3
]
e
BDI The three active stimuli (bright light, auditory stimuli, or
high-density negative ion exposure), but not the low-
density placebo, reduced depression, total mood
disturbance and/or anger within 1530 min.
The Profile of Mood
States Questionnaire
The Karolinska Sleepiness Scale
Likert scales assessed four aspects of stimulus perception
using a 7-point scale. Subjects rated stimulus hedonics and
intensity, as well as its effects on mood and on alertness
Terman and Terman,
2006[7]
b,d
Negative ion (93 minutes
before waking up)
Low density:
1.7 × 10
11
ions/s
[1 x 10
4
ions/cm
3
]
e
SIGH SAD Post-treatment improvement results were high-density
ions, 47.9%; and low-density ions, 22.7% (significantly
different).
High density:
4.5 × 10
14
ions/s
[2.7 x 10
7
ions/cm
3
]
e
Emergence or exacerbation of depression, sleep, appetite/
weight, headache
Gianinni et al.,
2007[26]
a
Negative ion (1 hour) 3 × 10
3
ions/cm
3
Brief Psychiatric Rating Scale A significant anti-manic effect was observed: total rating
scores declined with anion treatment.
Malcolm et al.,
2009[32]
a,b
Negative ion (30 minutes
pre-test and 60 minutes
during test)
Not reported Subjective state measured by six visual analogue scales for
happiness, sadness, hostility, alertness, anxiety and
calmness.
Association between BDI score and treatment; increased
recall and recognition of positive terms versus negative
terms; findings indicate that HDNI treatment produces a
positive bias in emotional recall and recognition.
The emotional test battery consisted of an emotional
categorization task with surprise emotional recall and
recognition, a facial expression recognition test, and a dot-
probe task of attention with masked and unmasked
conditions.
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Table 2 Air ion exposure assessment, psychological measures, and study findings (Continued)
Flory et al., 2010[4]
d
Negative ion (30 minutes for
12 days)
Low density:
4.0 × 10
3
ions/cm
3
SIGH SADSelf Rating: Subjects in all four groups showed significant score
decreases on the SIGH-SAD-SR and on the BDI. For raw
scale scores, neither main effects of treatment nor
interactions between treatment and time were significant.
When remission outcome criteria were used, exposure to
high-density negative ions was more effective than either
of the two placebo conditions, although the difference
was not significant.
High density:
2.0 × 10
6
ions/cm
3
BDI
Diagnostic and Statistical Manual of Mental Disorders
(DSM-IV) criteria for SAD
Malik et al., 2010[9]
a
Negative ion (2 hours) >1,000,000 counts/
cm
3
Self-reported computer-oriented stress, physiological and
psychological stress
A significant decline in computer-oriented stress and
psychological stress was noticed post-computer
operations in presence of negative ions.
Dauphinais et al.,
2012[24]
d
Negative ion (7.5 min/day or
15 min/day if tolerable for 8
weeks)
1.7 × 10
11
ions/s
[1 × 10
4
ions/cm
3
]
e
SIGH-SAD No significant difference in SIGH-SAD scores between
light therapy and low-density negative ion groups at
study end or in the proportions of responders or remitters
in these groups.
Harmer et al.,
2012[31]
a,b,d
Negative ion (30 minutes
pre-test and 60 minutes
during test)
Not reported Subjective state measured by six visual analogue scales
(happiness, surprise, sadness, fear, anger, and disgust), BDI,
and State-Trait Inventory
No effect on anxiety, depression (BDI), alertness, and recall
of emotional words. HDNI treatment decreased
recognition of faces showing disgust and increased
recognition of happy faces, and increased recognition of
and vigilance to positive words. HDNI increased
recognition memory of positive words only in the SAD
group. The findings indicate that HDNI treatment
produces a positive bias in emotional recall and
recognition.
The emotional test battery consisted of an emotional
categorization task with surprise emotional recall and
recognition, a facial expression recognition test, and a dot-
probe task of attention with masked and unmasked
conditions.
a
Activation, anxiety, mood.
b
Relaxation and sleep.
c
Personal comfort rating.
d
Depression.
e
Ions/s converted to ions/cm
3
for ionizers used in this laboratory based on Terman et al. [8].
f
Ion concentration in ion/cm
3
based upon Iwama et al. [41].
BDI beck depression inventory; CgA-like IR chromogranin A-like immunoreacitivity; HDNI high-density negative ions; SR self-rating; STAI-S state trait anxiety inventory scale; SIGH-SAD structured interview guide for the
hamilton depression rating scale, seasonal affective disorder.
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range: 2149; mean age: 26.4) rated their mood after
entering a sauna system on two occasionsone with
negative air ionization, the other without. The authors
observed no significant difference in reported mood
states betw een experimental and control conditions.
Nakane et al. [10] conducted a crossover study (blind-
ing not reported) among 12 female undergraduates (age
range: 1822) to examine the effect of negative air
ionization on anxiety and salivary chromogranin A-like
immunoreactivity (CgA-like IR), a pro tein indicator of
sympathetic nerve activity. The findings showed that
exposure to negative air ions significantly reduced anx-
iety compared to the positive control while performing a
computer-oriented task, but negative air ionization in
the post-task period was associated with a non-significant
reduction. Similar results were reported for CgA-like IR.
Goel and Etwaroo [5] performed a single-blind RCT to
determine the immediate effects of bright light, auditory
stimulus, and high-density (n=29) and low-density nega-
tive air ionization (n=30) on mood and attentiveness in
118 mildly depressed and non-depressed college students
(mean age: 19.4). The results showed that exposure to
high-density negative air ionization decreased depressive
symptoms, total mood disturbance, or anger within 15 to
30 minutes of exposure; however, low-density exposure
did not produce significant effects.
A double-blind crossover experiment by Gianinni et al.
[26] exposed 24 manic men (age range: 2329; mean age:
26.7) to high levels of ambient negative air ions and found
a statistically significant reduction in subjects mani c states.
In contrast, M alcolm et al. [32] conducted a single-blind
experiment among 30 healthy subjects (age range: 1828)
randomized to receive either high-density negative air ions
or a control condition and found no effect of exposure on
anxiety. Of note, the clinic that performed the Malcolm
et al. [32] study subsequently performed a double-blind
RCT of adults (21 patients with SAD and 21 controls)
exposed to high-density negative air ions and also reported
no effect on measures of visual analogue (mood) or State-
Trait Anxiety Inventory ratings [31]. When Malik et al.
[9] induced stress in 20 adults (age range: 2435; mean
age: 28.9) in a single-blind study by performing a com-
puter-oriented task, the subjects reported a significant
decrease in computer-oriented stress and psychological
stress following negative air ionization.
Gianinni et al. [36] researched the effects of positive
air ions only in a double-blind crossover study conducted
among 12 adult male volunteers and found that anxiety,
excitement, and serum serotonin levels significantly
increased when exposed.
Relaxation and sleep
Several studies examined the impact of negative and
positive air ionization on relaxatio n and sleepiness. In
the study by Silverman and Kornbleuh [27], more than
half of their 12 subjects reported one or more symptoms of
dryness of the mouth/upper respiratory tract, relaxation, or
sleepiness when exposed to either n egative or positive air
ionization; however, these responses were more prevalent
during negative air ionization. Yaglou [19] conducted a
single-blind crossover study in 25 healthy adults (age range:
2251) and a separate study in 6 arthritic patients (age
range: 3062) to examine the effects of negative and
positive air ionization on relaxation. In the first study of
25 adults, 5% reported feeling relaxed when exposed to
positive air ions; 17% reported feeling relaxed when ex-
posed to negative air ions; and 21% reported feeling
relaxed under control conditions [19]. In the second
study, a higher frequency of patients reported feeling
relaxed or sleepy, or both, when exposed to negative ver-
sus positive air ions [19].
Albrechtsen et al. [37] conducted two single-blind
experiments to evaluate the influence of negative and
positive air ionization on subjective feelings among two
groups: 6 randomly-selected women (age range: 2030)
and 12 adults (age range: 1945) who appeared to be
most sensitive to ionization. Outcomes included subjective
assessments on feelings of self-exertion, stuffiness, the
unpleasantness of cognitive tasks performed, and sleepi-
ness. Across both studies, no significant effects were iden-
tified. Hawkins [38] examined the influence of negative
and positive air ionization in an office environment on
personal ratings of thermal comfort, stuffiness, alertness,
and well-being in a double-blind crossover experiment
conducted over 12 weeks. Subjects (n=106) were divided
into groups based on areas of variable ionization levels.
Hawkins observed that negative air ionization was asso-
ciated with higher subjective ratings of alertness, atmos-
pheric freshness, environmental/personal warmth, and a
reduction in the overall complaint rate by 50%. Positive air
ion effects were not explicitly discussed.
Twelve studies examined the association of nega-
tive air ions only with relaxation and sleepiness
[5,7,8,11-14,22,29,32,34,39]. Assael et al. [11] conducted
a double-blind crossover study to examine the effects of
negative air ions on relaxation and alertness among 10
healthy participants (age range: 2065) and 10 subjects on
tranquilizers. The authors found that all patients reported
an initial relaxation followed by alertness when exposed to
negative air ions.
Three previously mentioned studies on air ions and
mood associations also evalua ted ion effects on relax-
ation or sleepiness, or both [12,29,34]. The double-blind
experiment conducted by Tom et al. [34] of 56 adults
assessed the impact of negative air ions on relaxation
(very tense versus very relaxed). Although reported
feelings of relaxation were slightly elevated in the experi-
mental compared to the control group, the findings were
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statistically non-significant. On the other hand, Buckalew
and Rizzuto [12] identified a significant increase in relax-
ation attributed to negative air ionization between ex-
perimental and control groups in their double-blind
study. In the work of Deleanu and Stamatiu [29], sleep
normalization was achieved in 53 of 67 patients with
insomnia who were exposed to negative air ions (blinding
not reported).
Lips et al. [13] performed a double-blind crossover trial
to examine the effect of negative air ions on alertness in
18 healthy adults. Subjects worked in either room one
with windows (natural ventilation) or room two with no
windows (mechanically ventilated). Lips et al. [13] ob-
served that following exposure to enhanced negative air
ions, subjects feelings of drowsiness were significantly
reduced within both rooms. In the pilot study by Misiaszek
et al. [14], all four subjects fell asleep and reported feeling
calm following negative air ionization in the first phase of
the study (non-blind). In the second phase (double-blind),
three of the four subjects fell asleep and one subject
appeared less agitated. In both phases, patients manic
behavior reappeared 5 to 10 minutes post-treatment [14].
Terman et al. [8] conducted a double-blind crossover
experiment to examine the effects of timed bright light
and negative air ionization on sleep timing in 124 sub-
jects (age range: 1859; mean age: 39.4), with 20 subjects
randomized to high-d ensity and 19 subjects randomized
to low-density negative air ionization. The findings
showed that exposure to high-density versus low-density
negative air ionization did not result in statistically
significant differences in sleep patterns. On the other
hand, Iwama et al. [39] conducted a double-blind experi-
ment with 44 patients randomized to the control and 51
patients randomized to receive negative air ion treat-
ment (mean age: 40). Five degrees of tension were
defined: 1=relaxed; 2=normal tension; 3=mild tension;
4=moderate tension; and 5=severe tension. The authors
found that treated patients tension reduced significantly
and quicker.
Goel et al. [22] conducted a double-blind RCT to
evaluate the efficacy of bright light and high-density
negative air ionization for non-seasonal chronic depres-
sion and sleep in 32 patients (age range: 2265; mean
age: 43.7). The findings show ed no significant change in
sleep onset between high-density (n=12) and low-density
(n=10) negative air ionization; but a significant alteration
in sleep offset was noted among the high-density
subjects. Similarly, in a single-blind study of light and air
ion treatment for depression, Goel and Etwaroo [5]
found no significant differences in subjects feelings of
sedation, pleasantness, or intensity. In a double-blind
RCT by Terman and Terman [7], 99 adults with SA D
(age range: 1963; mean age: 40.4) were followed to
examine the effects of high- and low-density negative air
ionization and light therapy during subjects final hours
of sleep. Sleep disturbances in 3 of 16 patients in the
low-density group were observed, but none in the
high-density group.
In a single-blind experiment of 30 healthy subjects (age
range: 1828) randomized either to receive high-density
negative air ionization or to a control condition, Malcolm
et al. [32] found no effect of air ionization on subjects
feelings of alertness or calmness. A subsequent double-
blind RCT of SAD patients and controls reported no effect
on patient alertness and found that negative air ion treat-
ment increased vigilance to unmasked positive items in
the visual dot-probe task regardless of patient group [31].
Personal comfort ratings
Three studies evaluated the impact of negative and po-
sitive air ionization on personal comfort [17,37,38].
McGurk [17] examined the effects of negative and posi-
tive air ions on self-reported feelings of comfort, ease of
working on cognitive tasks, and reactions to the test
room environment in 10 college-aged males undergoing
a single-blind experimental assessment. All subjects were
informed that on some days the air would be ionized; how-
ever, subjects remained uninformed about polarity. The
findings showed that negative air ion exposu re resu lted i n a
notable increase in the proportion of subjects reporting
more pleasant feelings, while positive air ion exposure ver -
sus the control condition resulted in a significantly higher
reporting of unpleasantness.
Findings in the Albrechtsen et al. [37] study found no
significant relationship between exposure to high con-
centrations of negative and positive air ions and feelings
of self-exertion, stuffiness, or the unpleasantness of
cognitive tasks among 25 healthy subjects or 6 arthritic
patients. In contrast, Hawkins [38] observed that nega-
tive air ion exposure was associated with higher sub-
jective ratings of alertness, atmospheric freshness, and
environmental/personal warmth among office employees
working in three different areas of variable air ionization
levels (double-blind study).
Several more recent studies [13,35,40] examined the
influence of exposure to negative air ions only on per-
sonal comfort among adults. Finnegan et al. [40]
conducted a single-blind experiment and found no sig-
nificant effect of negative air ionization on personal
comfort amon g 26 adults working within 5 different
rooms of an office building. On the other hand, Lips
et al. [13] examined the effects of negative air ion expos-
ure on personal comfort and well-being in a double-
blind study of 18 healthy adults who worked in either a
room with windows (normal environment) or one mech-
anically ventilated (ion-depleted environment). The find-
ings showed that following exposure to enhanced
negative air ions, subjects assessments of both their own
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well-being and their environments (room pleasantness
and comfort) imp roved significantly at both sites, but
failed to result in a significant difference in personal
thermal comfort scores. In addition, subjects in the ion-
depleted environment failed to experience an improve-
ment in air freshness during negative air ion exposure.
In the single-blind, ion-enhanced sauna study by Wata-
nabe et al. [35], no significant differences in the reported
feelings of plea santness between exposure settings were
observed.
Depression
All depression studies evaluated potential alterations
only from exposure to negative air ions [4-8,22,24,29,31].
In the study of 112 psychiatric patients by Deleanu and
Stamatiu [29], the findings showed that in over 50% of
45 treated patients diagnosed with depression, depressive
reactions attenuated or completely disappeared with
exposure to negative air ions (blinding not reported).
Terman and Terman [6] performed a double-blind RCT
among 25 patients (mean age: 38.2) to examine the effects
of negative air ions on SAD. Subjects were randomized to
low-density (n=13) or high-density (n=12) treatment. The
authors found that depression severity decreased (deter-
mined using SIGH-SAD) more notably for the high- than
the low-density treatment group. Applying a remission
criterion of 50% reduction in symptom severity, 58% of
patients reacted to high-density and 15% reacted to low-
density air ion exposure. Terman et al.s [8] double-blind
study of the effects of ti med bright light and negative air
ionization on SAD in 124 adults showed that exposure to
high-density air ionization provided subjects with clinically
significant relief by producing a 50% reduction in depres-
sive symptoms from baseline. In addition, the remission
rate associated with high-density negative air ionization
rose substantially with an additional 10 to 14 days of treat-
ment after the first period, but low-density exposure
showed no significant effect [8].
In their double-blind study evaluating the efficacy of
bright light and high-density negative air ion exposure for
non-seasonal chronic depression in 32 adults, Goel et al.
[22] observed a score improvement on the SIGH-SAD of
51% for high-density exposure (remission rate 50%) com-
pared to 17% for low-density exposure (remission rate 0%).
Similarly, Goel and Etwaroos [5] single-blind study of the
immediate effects of bright light (n=29), auditory stimulus
(n=30), high-density (n=29), and low-density negative air
ionization (n=30) in mildly depressed and non-depressed
adults indicated that exposure to high-density negative air
ions decreased depressive symptoms within 15 to 30 min-
utes; however, low-density exposure did not produce any
significant effects.
In a double-blind RCT by Terman and Terman [7], 99
adults with SAD or bipolar II disorder were followed to
examine the effects of high- and low-density negative air
ionization and light therapy during the final hours of
sleep. Study findings based on SIGH -SAD indicated that
exposure to low-density negative air ions resulted in a
significantly lower improvement (22.7%) in depression
scores compa red to improveme nt with high-density
exposure (47.9%). Flory et al. [4] also investigated the
effects of high- and low-density negative air ionization
and light therapy on SAD among 73 university-affiliated
women (age range: 1851; mean age: 20.8) in a single-
blind RCT and found that subjects in all study groups
showed significant score decreases on the SIGH-SAD
self-rating scale and the Beck Depression Inventory
(BDI) scale. Dauphinais et al. [24] performed a double-
blind RCT of adult patients with bipolar depression to
examine the effect of negative air ions. Subjects were
randomized to low-density (n=20), high density (n=2),
or bright light (n=18) treatment for 8 weeks. Of note,
the low-density group was considered the control and
too few data were available for the high-density group to
allow for a meaningful analysis; therefore, data among
the high-density group were not reported. The authors
found no significant difference between the depression
severity scores (determined using SIGH-SAD) of the
light and low-density treatment groups (52% vs. 47%
reduction, respectively) or between the proportion of
responders and remitters (light group50% of subjects
were either responders or remitters; low density ion
group55.6% of subjects in the low-density treatment
group were either responders or remitters).
Harmer et al. [31] exposed 21 SAD patients and 21
controls in a double-blind RCT to high levels of negative
air ions for 1.5 hours. Post-exposure measures of depres-
sion, as measured by the BDI scale, were unaf fected by
treatment. Additionally, SAD patients, but not controls,
exhibited an increased recognition memory for positive
words. The overlap in the results of this study with those
of Malcolm et al. [32], and parallels between air high-
density negative ion treatment and single-dose anti-
depressant administration on negative affective bias
[41,42], suggest a link between emotional processing of
certain stimuli and depressive states.
Meta-analysis of depression studies
The forest plots and overall weighted differences in
group means (i.e. pre- minus post-ion exposure mean
scores) by ion concentration (high/low) are shown in
Figures 1 and 2. Estimates of treatment effects for stud-
ies with multiple follow-up times [6-8] were examined
by time point also. Utilizing the later post-baseline mean
score where applicable, the weighted differences in group
means for the Atypical symptom subscale, Hamilton sub-
scale, and composite SIGH-SAD scale were 5.64 (95% CI:
4.44-6.85), 9.23 (95% CI: 8.52-9.94), and 14.28 (95% CI:
Perez et al. BMC Psychiatry 2013, 13:29 Page 14 of 20
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12.93-15.62), respectively (p for heterogeneity (SIGH-
SAD) = 0.94); thus, the results were indicative of a benefi-
cial effect of high-density negative air ion treatment on
SAD and treatment effects were comparable between
studies (Figure 1). The weighted differences in group
means in the low-density negative air ion analysis for the
Atypical symptom subscale, Hamilton subscale, and com-
posite SIGH-SAD scale were 1.98 (95% CI: 0.57-3.40), 4.87
(95% CI: 0.96-8.77), and 7.23 (95% CI: 2.62-11.83), re-
spectively (p for heterogeneity (SIGH-SAD) < 0.0001);
thus the results were also statistically significant, but smal-
ler in magnitude and were significantly different between
studies (Figure 2).
The findings were similar when utilizing the earlier
post-baseline mean score reported by Terman and
Terman [6,7] and Terman et al. [8] (results not shown);
however, the magnitude of effect by subscale and overall
was consistently smaller than those shown in Figures 1
and 2. Furthermore, the weig hted group mean difference
for the Atypical symptom subscale was statistically non-
Figure 1 High-Density Negative Air Ion Exposure and Depression. *Includes data from studies at the last follow-up time point where
applicable [6-8]; p for heterogeneity (composite SIGH-SAD) = 0.94. CI: Confidence Interval; SIGH-SAD: Structured Interview Guide for the Hamilton
Depression Rating Scale, Seasonal Affective Disorders.
Figure 2 Low-Density Negative Air Ion Exposure and Depression. *Includes data from studies at the last follow-up time point where
applicable [6-8]; p for heterogeneity (composite SIGH-SAD) < 0.0001. CI: Confidence Interval; SIGH-SAD: Structured Interview Guide for the
Hamilton Depression Rating Scale, Seasonal Affective Disorders.
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significant in the low-density negative ionization analysis
(mean=1.54 (95% CI: -0.31-3.39)).
Sensitivity analyses were performed by removing the
Terman and Terman [6] study since the data were
presented in a figure and not explicitly reported. These
analyses showed no alteration in the findings. An add-
itional assessment of exposure duration (hours), within
high- and low-density air ion levels, and each studys
score mean difference indicated no evidence of a dose
response relationship (Figure 3).
Publication bias was examined visually with funnel
plots, which allow for a visual assessment of the estimated
intervention effects from the individual studies plotted
against a measure of treatment effect size. Separate plots
were done for SIGH-SAD composite scores and SIGH-
SAD subscales combined since Terman and Terman [6]
reported estimates by subscale only and Terman et al. [8]
reported estimates for th e composite scale only. A clus -
tering indicative of publication bias was not observed
(Figure 4) (i.e., no marked asymmetry was evident). Statis-
tical evidence of publication bias was not found (Begg rank
correlation p=0.71; Egger regression p=0.37). These findings
were supported by those observed when combining the
Atypical and Hamilton subscales.
Discussion
This review and meta-analysis examined the relationship
between negative/positive air ion exposure and emotional
state in 33 human experimental studies published from
1957 to August, 2012. To our knowledge, this is the first
comprehensive review to summarize the liter ature on air
ionization and psychological outcomes. Also, no studies
have previously meta-analyzed the influence of high- and
low-density negative air ions on subjects depression
Figure 3 Doseresponse Assessment Between Exposure Duration as Measured by Hours, within High-Density Air Ion Levels, and Each
Studys Score Mean Difference. *Terman, 1998 [8] only provided data for the composite SIGH-SAD scale and not by subscale; Terman and
Terman [6] only provided data by subscale and not for the composite SIGH-SAD scale.
Perez et al. BMC Psychiatry 2013, 13:29 Page 16 of 20
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symptom severity. Our main findings were two-fold. First,
we failed to identify a consistent beneficial or detrimental
effect of negative or positive air ionization on mental well-
being based on studies of anxiety, mood, relaxation/sleep,
and personal comfort. Second, our meta-analysis of five
studies [4,6-8,22] on negative air ionization and depres-
sion suggested a decreased severity of symptom scores in
subjects with exposures to high air ion levels. Specifically,
we observed a decrease in depression scores, thus corre-
sponding to an improvement in subjects depressive state,
in comparisons of low- to high-density negative air ion
exposure (weighted mean score decrease of 7.23 and
14.28, respectively). A causal basis for this finding, how-
ever, was not presumed as the durations of exposure and
depression scores were not dose-related.
Exposures to air ions in low dose conditions slightly,
but significantly, reduced depression scores measured on
the SIGH-SAD. Indeed, no study reported that low dose
exposure produced a clinically significant reduction in
depression (criterion applied by Terman et al. [8]; Flory
et al. [4]; Terman and Terman [6]) of greater than 50%.
In fact, it appears that low dose ionization may be
regarded by these investigators as an inactive exposure
condition [22,24].
Although our meta-analysis showed that exposures to
high levels of negative ions was associated with a signifi-
cant improvement in rated depression severity as mea-
sured using SIGH-SAD, a primary metric for both
seasonal and non-seasona l depression [4,43-46], and a
lack of statistical heterogeneity across study results in
the high-density analysis was observed, the findings
should be cautiously interpreted. First, this body of work
typically did not control for or failed to report on envir-
onmental factors affecting exposure including the
electric fiel d, air flow, humidity, and temperature. It is
well known that the spatial distribution and numbers of
air ions vary considerably due to differences in these fac-
tors [47]. Hence, the findings summarized herein are
likely impacted by unmeasured variables within the
available studies and the extent of this impact remains
unknown. Second, air ion concentrations for high- and
low-density were different across studies, ranging from
4.0 × 10
3
ions/cm
3
to 1.0 × 10
4
ions/ cm
3
for low-
density and from 2.7 × 10
6
ions/cm
3
to 2.7 × 10
7
ions/
cm
3
for high-density (except for Flory et al. [4], who
defined high-density as 2.0 × 10
6
ions/cm
3
). Our finding
of statistically significant heterogeneity across studies in
the low-density analysis is likely impacted by these varying
exposure levels, whereas the effect of high-density air ion
treatment may occur independently of the range of expos-
ure levels if an effective exposure threshold is exceeded.
Given that at most two studies reported the same air ion
concentrations for high- and low-density, however, we
could not justify performing separate meta-analyses by ion
concentration. However, when hours of exposure were
considered as a surrogate for dose within the high- and
low-density analyses, repeated or longer exposure dura-
tions to negative air ions failed to produce a greater effect
on depression scores than did shorter durations. Third, all
studies included in the meta-analysis except Flory et al. [4]
were conducted by a single research group, which pro-
vides little independent replication and may explain, in
part, the low between-study variance observed in the
high-density analysis. Fourth, differential effects, if any, be-
tween men and women were not examined. Gender-
stratified analyses are important to consider given that the
pharmacokinetics, pharmacodynamics, and hormonal
effects between men and women differ and likely influ-
ence depression severity [48]. Finally, some depression
studies [5,24,29,31] included in our narrative review were
unable to be meta-analyzed because of the heterogeneous
reporting of available data and the use of different metrics
for assessing depression (e.g., BDI and subjective assess-
ments on the amelioration of depressive reactions). Add-
itional experiments are warranted to clearly understand
the impact of negative air ionization on depression sever-
ity and how findings may be influenced by variable con-
centration levels and different metrics for symptom
measurement. Future studies should aim to determine the
efficacy of high-density air ion therapy for treating depres-
sion among men and women. Studies should also aim to
evaluate the specificity of any response(s) to negative air
ions by testing positive air ions as well.
Based on our review, there is no scientific basis for
concluding that air ions have a beneficial or adverse
effect on measures of anxiety, mood, relaxation/sleep,
and personal comfort in the range of exposures reviewed
(200300 ions/cm
3
(ambient levels) to 10
6
ions/cm
3
).
Figure 4 Visual Assessment of Publication Bias Using a Funnel
Plot (SIGH-SAD composite scores). *A clustering indicative of
publication bias around the mean treatment effect was not
observed (i.e., no marked asymmetry was evident). In the absence of
publication bias we would expect the studies to be distributed
symmetrically about the combined treatment effect.
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The quality of many studies, however, is low and there
are several important inconsistencies across studies (e.g.
differential study settings/populations, follow-u p periods,
exposure/outcome measurement and assessment, and
unmeasured confounders such as temperature). Of par-
ticular importance is the heterogeneity observed in the
frequency, duration, and intensity of air ionization evalu-
ated. Presumably, the greater the ion concentration,
combined with longer exposure durations at greater
frequency, the greater the likelihood for air ion exposure
to produce a biological response in exposed subjects, if
in fact a real association is present. While the re is no
consistent support in animal studies for effects of
negative or positive air ion treatment on central nervous
system neurotransmitter systems linked to depression
[21,49,50], Dowdall and De Montigny [51] have reported
that continuous exposure of rats to negat ive air ions at
a density of 1.5 × 10
6
ions/cm
3
for 21 days increa-
ses the response of hippocampal pyramidal neu rons
to iontophoretically applied serotonin as do several
antidepressant drugs. Nonetheless, human studies to
date on the relationship between exposure duration,
within high and low air ion c oncentrations , and
depression symptom severity do n ot support such a
relationship. In addition, variable distances between
subjects and th e location at which ion generators
were situated likely influenced the number of air ions
reaching the subject s. Ba s ed on the exposure a ssess -
ment alone, proper comparison across studies is
therefore quite difficult due t o the varying exposure
assessment s, differences in air ion systems use d, and
disparate monito ring of ion levels. A d isparity in the
measurement and a ssessment of the outcomes e valu-
ated also rende rs a comparison across studies diffi-
cult. In this regard, instrument s other than the SIGH-
SAD to measure depression severity (e.g., the BDI
[52], the Center for Epidemiological Studies Depres-
sion Scale [53], the Zu ng Self-R ating Depression Scale
[54]) might be considered in future studies since dif-
ferent depression scales may vary in sensitivity and
specificity for depression severity, may differ in the
measurement of different construct(s) based on the
inclusion of specific sur vey ite ms (i.e., items may dis-
criminate between different dimensions of depression),
and may be more suited over others in specific target
populations (e.g., young adults vs. elderly patients). Fur-
thermore, no study reported responses to air ion therapy
by gender. Specific tests for differential responses, how-
ever, would have been of interest given that gender
specific-differences are reported in the literature for many
emotional parameters [55-57].
Though major limitations of the studies reviewed have
been discussed, we acknowledge certain strengths. Since all
studies were experimental, most, but not all, observations
were made within a controlled environment and prospect-
ively. In addition, participants in 2830 studies remained
blind to exposure and ion density, thus mitigating potential
bias. Blinding of the experimenters was less common
(1618 of 2830). Such precautions should be taken in future
studies to minimize introducing possibl e bias by subjects
and investigators. In our review, subject expectations in
some studies were compared with depression ratings at the
study end. Some studies found no association between
expectations and the outcome, suggesting minimal bias
[5,8], while other more recent studies reported a significant
relationship [4,7].
The W orld Health Organization conducted a community-
based study in 14 countries on the prevalence and severity
of mood disorders and found that the 1-year prev a-
lence of mood and anxiety diso rders in developed
nations ranged from 3.1%-5.3% in Japan to 9.6%-18.2%
in the US [58]. Kessler et al. [59] used the National
Comorbidity Survey Replication to estimate the life-
time prevalence of DSM-IV disorders and reported life-
time prevalence estimates for mood (20.8%) and anxiety
disorders (28.8%). An earlier report by Kessler et al. [60]
found that lifetime prevalence for clinical depression
among US adults was 16.2% and 1-year prevalence was
6.6%. Globally, the burden of mood disorders such as
depression is on the rise, with only 30% of cases world-
wide receiving appropriate care for depression [61].
Hence, mood and anxiety disorders present a global crisis
that heavily burdens society with serious implications for
daily quality of living, economic costs, and the need for
individually-tailored treatment.
Conclusions
Our narrative review provides no basis for further inves-
tigation of a variety of emotional state indicators and air
ionization. Our meta-analysis, however, strengthens the
rationale for further study of high dose negative
ionization (>2.7 × 10
6
ions/cm
3
) on depression severity,
an effect, if real, that remains to be fundamentally
understood. Such studies should apply a double-blind
design with rigorous control over air ionization and
potential confounding, including placebo effects. In ad-
dition, using validated metrics for outcome assessment
in large study populations; determining justifiable thre-
sholds to delineate between sham, low, and high air ion
concentrations; and implementing an adequate exposure
duration and follow-up period are recommended. Given
that longer or repeated exposures to negative air ions
were not observed to strengthen the response of
subjects, additional investiga tion of the biological plausi-
bility is warranted. The concentrations of air ions ex-
pressed as parts per trillion are vanishingly small and
well-controlled animal studies do not report changes in
catecholamine neurotransmitter levels [50] or the levels
Perez et al. BMC Psychiatry 2013, 13:29 Page 18 of 20
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and turnover of serotonin in the brain [49] even though
opposing effects of longer-term exposure to negative
and positive air ions on the responsiveness of hippocam-
pal neurons to serotonin have been reported [51].
Competing interests
WHB has consulted for AltaLink LLC, and public and private electric utilities
in the preparation of environmental impact assessments and assisted
scientific organizations, regulatory agencies, and health agencies to keep
abreast of current research involving exposures relating to the use and
transport of electricity.
Authors contributions
WHB conceptualized the study and led the design, data acquisition, and
interpretation. VP, DDA, and WHB collaborated on the data acquisition,
analysis, and interpretation. VP drafted the manuscript. VP, DDA, and WHB
provided critical revisions of the manuscript for important intellectual
content. WHB provided supervision. All authors read and approved the final
manuscript.
Authors information
VP was awarded her Ph.D. in epidemiology from the University of Michigan
at Ann Arbor. Her research primarily focused on the impact of psychological
stress on the health of young adults in the community setting. DDA was
awarded his Ph.D. in epidemiology from the University of Alabama at
Birmingham. He has conducted numerous state-of-the-science reviews and
weight-of-evidence assessments on complex medical and scientific issues.
WHB was awarded his Ph.D. in neuropsychology from the City University of
New York for research at The Rockefeller University, where he continued for
postdoctoral research in neurochemistry. He has been involved in air ion
research since 1982 and served as a science advisor to the Minnesota
Environmental Quality Board and the Vermont Department of Public Service
on health and safety issues relating to air ions.
Acknowledgements
The authors gratefully acknowledge the research contributions of Nancy
Rivera in the preparation of this manuscript and the invaluable comments
from Drs. Catherine Harmer and Timo Partonen.
Funding
This work was partially funded by a research grant from AltaLink LLC;
however, the writing, data review, and interpretation were conducted
independently by the authors.
Author details
1
Exponent, Inc., Health Sciences, Center for Epidemiology, Biostatistics, and
Computational Biology, 525 West Monroe Street, Suite 1050, Chicago, IL
60661, USA.
2
Exponent, Inc., Health Sciences, Center for Epidemiology,
Biostatistics, and Computational Biology, 4141 Arapa hoe Avenue, Suite 101,
Boulder, CO 80303, USA.
3
Exponent, Inc., Health Sciences, Center for
Exposure Assessment and Dose Reconstruction, 17000 Science Drive, Suite
200, Bowie, MD 20715, USA.
Received: 16 May 2012 Accepted: 8 January 2013
Published: 15 January 2013
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doi:10.1186/1471-244X-13-29
Cite this article as: Perez et al.: Air ions and mood outcomes: a review
and meta-analysis. BMC Psychiatry 2013 13:29.
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Perez et al. BMC Psychiatry 2013, 13:29 Page 20 of 20
http://www.biomedcentral.com/1471-244X/13/29
... Wind speed is closely related to air ions, and exposure to positive air ions may be harmful, while exposure to negative air ions may be associated with beneficial health effects (Krueger and Reed 1976;Nastos et al. 2017;Della Vecchia et al. 2021). Exposure to high levels of negative air ions may be associated with improvements in depressive symptoms (Perez et al. 2013;Jiang et al. 2018). In addition, high wind speed lead to increased noise from air rushing friction, which may affect the central nervous system, making people feel nervous and irritable. ...