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195
International Journal of Circumpolar Health 65:3 2006
HEALTH EFFECTS AND RISKS OF
SAUNA BATHING
Katriina Kukkonen-Harjula, Kyllikki Kauppinen
UKK Institute for Health Promotion Research, Tampere, Finland
Received 1 February 2006; Accepted 2 May 2006
ABSTRACT
Objectives. To study physiological, therapeutic and adverse effects of sauna bathing with special
reference to chronic diseases, medication and special situations (pregnancy, children).
Study design. A literature review.
Methods. Experiments of sauna bathing were accepted if they were conducted in a heated room
with sufcient heat (80 to 90ºC), comfortable air humidity and adequate ventilation. The sauna
exposure for ve to 20 minutes was usually repeated one to three times. The experiments were
either acute (one day), or conducted over a longer period (several months).
Results. The research data retrieved were most often based on uncontrolled research designs with
subjects accustomed to bathing since childhood. Sauna was well tolerated and posed no health
risks to healthy people from childhood to old age. Baths did not appear to be particularly risky
to patients with hypertension, coronary heart disease and congestive heart failure, when they
were medicated and in a stable condition. Excepting toxemia cases, no adverse effects of bathing
during pregnancy were found, and baths were not teratogenic. In musculoskeletal disorders, baths
may relieve pain. Medication in general was of no concern during a bath, apart from antihyper-
tensive medication, which may predispose to orthostatic hypotension after bathing.
Conclusions. Further research is needed with sound experimental design, and with subjects not
accustomed to sauna, before sauna bathing can routinely be used as a non-pharmacological treat-
ment regimen in certain medical disorders to relieve symptoms and improve wellness.
(Int J Circumpolar Health 20 06:65(3):195-205.)
Keywords: sauna bathing, cardiovascular diseases, medication, pregnancy, heat
REVIEW
196 International Journal of Circumpolar Health 65:3 2006
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INTRODUCTION
Sauna bathing is a special form of heat expo-
sure characterized by a short-term exposure
to exceptionally high environmental tempera-
tures. It is an ancient habit in both cold and
warm climates. Sauna bathing is still popular
in many northern circumpolar countries and,
during the past decades, it has also become a
widely practiced wellness form in many central
European countries. Virtually all Finns are
used to weekly bathing since early childhood.
The sauna is a log, or wood-paneled room,
where the bathers relax on benches well above
the oor level in the heat from the heater
constructed of, or lled with, rocks. The hot
room air temperature falls within the range
of 70 to 100°C, optimally between 80 and
90°C at the face level of the bathers. The air
humidity, modied by bathers tossing water
on the heated rocks, ranges from 15 to 30%
relative humidity (r.h.) at the recommended
temperatures.
The sauna bath consists of repeated cycles
of exposure to heat and cold. The length of
stay in the hot room depends on each bath-
er’s own sensations of comfort; the duration
usually falls between ve and 20 minutes.
This is followed by a cool-off (shower, swim,
or a period at room temperature), the length of
which also depends on personal sensations (1).
A sufcient recovery period (usually about one
half of an hour) following a few hot/cold cycles
allows for normalizing the body temperature
and cessation of sweating.
During the past half a century, a consider-
able amount of research data on sauna bathing
has originated especially from Germany and
Finland. During the past 10 years, innovative
experiments investigating new therapeutic
uses of sauna bathing have been performed in
Japan (2).
The aim of this review is to present physi-
ological, therapeutic and adverse effects of
sauna bathing, particularly in cases of chronic
diseases, with special reference to cardiovas-
cular diseases and to medication. The habit of
ice-water immersion without sauna bathing
(see 3-5) will not be discussed. The literature
search was based on Medline and on own
personal les. Experiments (either acute, or
conducted over a longer period of up to several
months) were accepted, if bathing conditions
(temperature, humidity, length of exposure)
complied with the above-mentioned descrip-
tion of sauna bathing.
PHYSIOLOGICAL EFFECTS OF SAUNA
BATHING IN HEALTHY PERSONS
The overall physiological effects of sauna expo-
sure have been presented previously (e.g. 6).
The cardiovascular system combats the
thermal stress by cutaneous vasodilatation,
and increased skin blood ow, heart rate and
sweating. The heart rate accelerates up to
twice the resting rate and even more (7, 8).
The cardiac output is estimated to increase
by about 70 % over the resting state, the total
peripheral resistance of the vessels decreases
by about 40 % (9), the stroke volume is unaf-
fected, and the diastolic and mean arterial
pressures decrease, with practically no change
in the systolic pressure (7). The overall work of
the heart, as estimated from the heart rate and
systolic blood pressure, indicating myocardial
oxygen demand, does not increase greatly (6).
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International Journal of Circumpolar Health 65:3 2006
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The strain on the heart and the cardiovascular
system depends not only on the temperature in
the hot room, its air humidity and the duration
of stay in the heat (8), but also on the type of
cooling employed during the cool-off session.
The skin temperature uctuates from up to
40°C in the hot room, down to 33°C upon ice-
water immersion (1). The core temperature, as
measured from the esophagus, is more stable,
rising in the hot room at an average rate of
0.07°C × min-1 up to 38°C, then accelerating to
0.4°C × min-1 up to 39°C, and returning to initial
values rapidly after the exposure. The rate of
reduction depends on the type of cool-off (1).
Sweating results in a weight loss of about 0.5
to 1 kg. The water should be replenished by
drinking during, or after the sauna bath (10).
Athletes in sports performed in weight classes
often use prolonged sauna bathing to decrease
their weight rapidly. However, this can impair
sports performance (11).
The sympathetic nervous system and the
hypothalamus-pituitary-adrenal hormonal
axis are activated to maintain thermal balance
(6, 12). The overall effect of the hormonal
changes is water retention and a ght-or-
ight response of the organism, manifested as
reduced perception of pain, elated mood and
alertness. The thermal challenge of the bath
cycle is reected in increased plasma concen-
trations of noradrenaline (13, 14). The adren-
aline concentrations have been reported to
remain unchanged, or to increase. The discrep-
ancy is due to different bathing patterns, espe-
cially the type of cool-off, and to different
blood sampling techniques (12). When blood
samples were taken in the hot room and the
subjects were moved in wheelchairs for cool-
offs, plasma adrenaline concentrations were
elevated during bathing in young women (15).
Sauna with cool-offs at room temperature
did not elicit increased circulating adrenaline
levels, whereas a sauna alternated with ice-
water immersion resulted in increased adrena-
line in persons used to winter swimming (14).
The bath cycles elicit secretions of ACTH
in some studies (8, 13, 14) and, especially with
ice-water immersion, of cortisol (14). Plasma
growth hormone, prolactin and β-endorphin
have also been reported to increase (8, 13). The
reduced plasma volume (16) and loss of sodium
in the sweat activate the renin-angiotensin-
aldosterone system (12). The plasma arginine
vasopressin levels and the plasma atrial natriu-
retic peptide concentrations rise during a bath
(17). In men, the plasma testosterone concen-
trations do not change. Evidence of regular
sauna bathing reducing male fertility was not
found. A two-week sauna exposure altered
sperm movement characteristics, but they
were reversed within one week after the end of
bathing sessions (18).
A comfortable relative humidity of 15 to 30
% keeps the mucous membranes of the upper
airways moist (19). Provided that the sauna
air is hot enough, about 80 to 90°C, there is
no concern about viable micro-organisms
being inhaled. The respiration becomes more
frequent and shallow, while the total respi-
ratory minute volume increases. The vital
capacity (VC), the peak expiratory ow rate
(PEF), and the forced expiratory volume in
the rst second (FEV1) all increase, implying
improved pulmonary ventilation. All changes
are minor, roughly 10 %, and initial levels
are reached quickly after the sauna (19). The
diffusing capacity did not change in healthy
subjects (20).
198 International Journal of Circumpolar Health 65:3 2006
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THERAPEUTIC EFFECTS OF SAUNA
BATHING IN CHRONIC DISEASES
The effects of sauna bathing in the course of
various diseases have been previously reviewed
by Kauppinen (21), Keast and Adamo (22),
Hannuksela and Ellahham (23), and Nguyen
et al. (24).
Cardiovascular diseases
People with cardiovascular disorders are some-
times discouraged to enter a sauna. The bulk
of scientic evidence, however, supports the
view that persons with cardiovascular diseases
in stable state with medication (e.g., essen-
tial hypertension, coronary artery disease, or
compensated heart failure) may safely take
their sauna baths (23, 25). In addition, there is
no evidence that a bath would provoke throm-
botic episodes, or bleeding tendencies (6).
A study on 69 Finnish patients with
myocardial infarction and 32 healthy persons
showed that, four to six weeks after the inci-
dent, bathing was harmless (25). Only 8 %
of them had cardiac dysrhythmias during
bathing, compared to 18 % during a submax-
imal exercise test. A ten-year follow-up study
of 117 patients who had suffered myocardial
infarction (9) found only one patient who had
chest pain during or soon after a bath. On the
other hand, 60 % of the patients experienced
angina during normal daily life, in instances
other than bathing. Myocardial ischemia and
dysrhythmias were more pronounced during
an exercise test and walking, or jogging
outdoors than in connection with a sauna bath.
The load on, and the oxygen demand of, the
heart during bathing remained at a lower level
than under comparable physical or emotional
stress.
Myocardial ischemia during sauna bathing
and in a maximal exercise test was assessed in
16 U.S. patients with coronary heart disease,
using scintigraphic imaging (26). When
compared to rest, perfusion defects suggesting
myocardial ischemia were observed more
often during exercise than bathing, and ST
depression in electrocardiograms occurred
only in exercise.
During the past 10 years, interventions
have been conducted in Japan to use sauna
bathing as one component of the treatment of
congestive heart failure. Previously, hot sauna
was considered as a contra-indication for this
condition, but a milder form of sauna-like
exposure (60°C, dry air) was used in the Japa-
nese studies. Acute effects of sauna and hot
tub bath were compared in patients with heart
failure (27). Both heat exposures increased
the oxygen consumption by 0.3 MET (1 meta-
bolic equivalent equalling the resting energy
expenditure), increased the heart rate by 20
to 25 beats per minute, did not change the
systolic pressure during the heat exposure and
reduced it afterwards, increased the cardiac
output by 1.5 to 2.0-fold, reduced the total
peripheral resistance greatly and increased
the left ventricular ejection fraction. Hemo-
dynamics improved more after the hot air
bath than after the tub bath.
A further study compared the effects of two
weeks’ sauna bathing in patients with cardiac
failure (28). Endothelium-mediated vasodila-
tion was enhanced, in addition to a decreased
left ventricular end-diastolic dimension and
decreased circulating concentrations of brain
natriuretic peptide. Symptoms were improved
in most patients (2). An improvement in
impaired vascular endothelial function after
two weeks’ bathing was also seen in men
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International Journal of Circumpolar Health 65:3 2006
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with cardiovascular risk factors, but without
cardiac failure (29).
In a randomized controlled study, patients
with heart failure underwent sauna bathing on
ve days weekly for 2 weeks (30). Compared
with the non-treated group, premature
ventricular contractions decreased and heart
rate variability increased, which might have
prognostic signicance.
Musculoskeletal diseases
Sauna bathing has been used to relieve pain
in various musculoskeletal disorders, often
due to degeneration. The mechanism for the
heat-induced sedative effect might be medi-
ated through sensory nerves in the skin. When
heat stress is combined with intense cool-offs,
it may result in analgesia, which is reected by
increased levels of circulating β-endorphins
(12). This may enhance immunosuppressive
and anti-inammatory functions.
A peculiar nding in persons with rheu-
matoid arthritis, osteoarthritis and especially
bromyalgia, is that, while the sauna heat
presently alleviates the pain, there may be a
delayed effect of worsening pain the next day.
During bathing, pain increased in only about
10 % of persons with neuropathic, or rheu-
matoid pain (31). Within 12 hours following
the bathing, about 50 % of arthritis patients
reported exacerbation of pain. The increased
serum concentration of prolactin may be the
mediator. By experience, some patients have
learnt to prevent this ”hangover” by inten-
sive cooling after bathing (32). In a nonran-
domized six-week treatment study, women
with bromyalgia, but without previous
sauna use, increased their pain tolerance
more after sauna bathing than after aquatic
therapy (33).
Bathing has also been used to prevent
exercise-induced musculoskeletal pain. The
delayed onset muscular soreness that often
follows eccentric muscular work was studied
in untrained young women (34). After an exer-
cise session, they were randomly subjected
to a sauna bath, a hot water bath, a neutral
water bath, or no heat, and the exposure
was repeated after two days. The maximal
strength, subjective pain, pressure threshold
of pain and serum enzymes indicative of
muscular cellular damage, were assessed daily
for nine days after the exercise. The hot bath
induced the least decrease in the strength and
the least increase in the pain or the enzyme
concentrations, when compared to a neutral
bath. On the other hand, sauna bathing did not
prevent soreness, when compared to no heat
exposure.
Depression
There is some recent Japanese evidence
that sauna bathing might be benecial in
depressed, or fatigued persons. In a random-
ized controlled study, non-obese patients with
mild depression underwent sauna-like expo-
sure on ve days weekly for two weeks (35).
Compared with the control group, somatic
complaints, hunger and relaxation scores
improved, while concentrations of plasma
ghrelin, an orexigenic hormone, and daily
energy intake, increased.
Respiratory diseases
Some respiratory diseases, especially chronic
obstructive pulmonary diseases (COPD),
tolerate the sauna well. During bathing, 12
men with COPD experienced an improvement
in FVC and FEV1, and most of them described
decreased respiratory effort (36). On the other
200 International Journal of Circumpolar Health 65:3 2006
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hand, bathing did not enhance tracheobron-
chial clearance in ve men with chronic bron-
chitis (37). Based on this meager evidence on
COPD, bathing does not seem to cause any
harm, but neither does it improve the condi-
tion permanently.
Asthmatics usually feel that the heat in
sauna relieves their respiratory effort. The
mechanism is proposed to be mediated by
increased concentrations of circulating cate-
cholamines, which relax the bronchial smooth
muscle. Fourteen asthmatic children were
studied during weekly sauna bathing for seven
weeks (38). No signicant changes in PEF
were observed before and after sauna, and
after cooling.
The common cold is believed to be fended
off by regular bathing. In a nonrandomized
study, 25 adults unaccustomed to sauna were
submitted to bathing once or twice a week for
six months, while the control group abstained
from any hyperthermic exposures (39). For the
rst three months, the incidence of common
cold was about equal in the two groups. During
the latter three months, however, the incidence
among the sauna goers was less than one half
of that among the control group.
RISKS AND ADVERSE EFFECTS OF
SAUNA BATHING
Cardiovascular catastrophies,
and accidents
The most dreadful adverse effect during a
sauna bath, or within the rst 12 hours after-
wards, is sudden death, which most often is due
to underlying, though not always previously
diagnosed, cardiovascular disease. However,
both the absolute and relative risks are small.
In Finland in the 1970’s, sudden deaths among
men over 60 years occurred at a rate of 1 per
0.4 million sauna baths, while the rate for 50 to
59-year-olds was 1 per 2.3 million and for 40
to 49-year-olds 1 per 9 million (40).
Other severe adverse effects are due to
accidents, such as burns from the heater (41,
42) and drowning during a cool-off swim.
Alcohol is often a contributing factor (43, 44).
Alcohol consumption can also enhance the
risk for hypotension. However, bathing, even
in combination with heavy alcohol drinking,
does not appear to provoke cardiac dysrhyth-
mias in healthy young men (45).
Pregnancy
Sauna bathing as a source of hyperthermia
has been suggested to be teratogenic in early
pregnancy (46). When studying the relation-
ship between heat and birth defects, the use of
sauna, hot water baths and electric blankets, as
well as having a fever, or living in a hot climate,
have been used as examples of hyperthermia.
About two decades ago, central nervous system
defects, anencephaly and spina bida were
claimed to result from sauna baths during the
rst two months of pregnancy, which coincides
with the time for organogenesis. However, the
incidence of anencephaly in Finland, where 95
to 99 % of pregnant women take sauna baths
once weekly, or more, throughout their preg-
nancies, is lower than anywhere in the world
(47). Incidentally, in regions with high inci-
dences of anencephaly, such as Belfast and
Dublin, women do not seem to have fever, or
take hot baths, more often than those in other
regions (48).
Congenital cardiovascular malformations
are the most common birth defects. No asso-
ciation was found between maternal sauna
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International Journal of Circumpolar Health 65:3 2006
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bathing, the course of gestation, or the occur-
rence of congenital defects in a Finnish study
(a three-year national material with about
500 cases and 1000 healthy control babies)
(49). Similar results on the use of hot baths
and sauna have been reported from New York
(50). Nor was the risk increased in Finland
for defects of the central nervous system and
of orofacial clefts (51), or heart defects (49).
To our knowledge, experimental studies
on the effects of sauna bathing on pregnant
women and their fetuses have only been
carried out in Finland (15, 52). Two groups of
pregnant (early and late stage) women were
acutely exposed to sauna-like heat exposure,
as were 15 non-pregnant control women. In
both pregnant and control women, the rectal
temperature rose 0.3 to 0.5°C during the expo-
sure, i.e., not enough to reach the supposed
teratogenic level of 38.9°C, while the skin
temperature rose by about 5°C. In pregnant
women, no changes were found in umbilical
artery blood ow. All deliveries took place at
the estimated time, and the newborn infants
were all in good condition at delivery.
Thus, during uncomplicated pregnancies,
sauna baths neither seem to harm the fetus,
nor are they dangerous to the mother. On the
other hand, the resistance to the blood ow in
the uterine artery was increased in toxemic
patients subjected acutely to sauna-like
thermal challenge, while no such event was
recorded in normal controls (53). In severe
toxemia, the fetal compensation mechanisms
may already be utilized maximally at room
temperature, and the heat exposure might
compromise the availability of oxygen to the
fetus. Therefore, pregnant mothers suffering
from toxemia are advised to avoid the sauna
bathing.
Children
It is often believed that children should take
sauna baths because of its dangers. Yet, most
children in Finland are introduced to the
sauna at the mean age of ve months, and
they continue to take a sauna bath at least
once a week throughout life (54). However,
there has only been one physiological study
on sauna bathing in healthy infants (mean age
seven months) (55). A three-minute exposure
induced no harmful cardiovascular responses.
The sauna places greater demands on a
child’s circulatory regulation than on that of
adults. The maintenance of homeothermia,
as studied in 20 children aged 5 to 10 years
(56), resulted in moderate hormonal changes.
Under adequate adult supervision, healthy
children over two years of age may well be
allowed in a sauna (57). The most common
problems related to sauna bathing of children
are accidental burns and scalds by hot water
(58). There is a risk of vasovagal collapse at
the very beginning of the cool-off phase. The
heat stress may be risky for those children
who have disorders of the sinoatrial node of
the heart (56).
Sauna-like heat exposure bathing was used
as vasodilative therapy in 12 infants aged
1 to 4 months, who had severe heart failure
due to ventricular defects (59). A four-week
daily therapy improved hemodynamics and
decreased symptoms, and surgical repairs
were avoided in 9 patients.
Contra-indications to sauna bathing
Based on both physiological and adverse
effects of bathing, contra-indications include
prolonged, or unstable angina-type chest
pain, myocardial infarction, or other severe
cardiac events for four to eight weeks after the
202 International Journal of Circumpolar Health 65:3 2006
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incident, severe orthostatic hypotension and
severe aortic stenosis (9, 25), acute infectious
diseases with fever, rheumatoid arthritis in
the acute inammatory phase (32), fever for
any reason, and certain skin conditions, such
as cholinergic urticaria, abrasions and oozing
rashes (60).
MEDICATION AND SAUNA BATHING
Since bathing induces changes in body temper-
ature, circulation and uid balance, drug phar-
macokinetics, or responses to drug therapy,
may be affected. Absorption, metabolism and
elimination of drugs may be altered, as well as
the responses to drugs affecting the autonomic
nervous system and cardiovascular system. A
review by Vanakoski and Seppälä (61) gives
an overall presentation of pharmacokinetics
under various hyperthermic conditions.
It has been proposed that, if sauna decreases
the hepatic circulation, it may inuence drugs
with hepatic rst-pass metabolism (e.g., mida-
zolam, propranolol). Indocyanine green was
used as an indicator of hepatic circulation (62).
Its clearance was not changed during bathing
in healthy individuals. The metabolism of
midazolam (a short-acting hypnotic) was not
altered either (63).
Ephedrine and tetracycline are both
excreted through the kidneys. Renal excretion
of ephedrine was unaffected (64) by bathing,
and the effects of sauna on tetracycline (65)
pharmacokinetics were modest in healthy
individuals.
Several cardiovascular drugs, including-
nitroglycerin, β-adrenergic blocking agents,
calcium channel antagonists, and ACE
inhibitors, have been studied in sauna (61).
β-blocking agents prevent the heat-induced
increase in heart rate. Generally, antihyper-
tensive medication taken immediately before
bathing is not advisable, because it parallels,
or amplies, the hypotensive effects (espe-
cially on diastolic pressure) of post-sauna
relaxation. However, diltiazem did not poten-
tiate sauna-induced vasodilation in hyperten-
sive patients (66).
Systemic sympathomimetics (e.g., ephe-
drine) and parasympatholytics (e.g., scopo-
lamine) may enhance the sauna-induced
effects of increased sympathetic activity, and
of elevated heart rate and blood pressure,
so that their administration shortly before
bathing should be done with caution. The use
of drugs affecting the autonomous nervous
system, such as scopolamine, atenolol, or their
combination, did not have harmful effects on
healthy young men during bathing (67).
As bathing increases cutaneous blood ow,
it may increase the absorption of transder-
mally administered drugs. Indeed, the use
of transdermal glyceryl trinitrate (nitroglyc-
erin) (68) and nicotine (69) patches increased
plasma concentrations of nitroglycerin and
nicotine in healthy subjects after bathing;
headaches, a clinical sign of enhanced absorp-
tion of glyceryl nitrate, were experienced (68).
From experience, many coronary patients
know the nitroglycerin-like effect of sauna
(i.e., vasodilation) and, therefore, avoid
taking such drugs shortly before bathing. By
a physiological mechanism similar to that of
transdermal administration, insulin absorp-
tion from a subcutaneous injection site in
diabetics was enhanced during bathing (70).
Another issue when using transdermal drug
administration in the form of patches, is their
adhesion stability to skin in various tempera-
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International Journal of Circumpolar Health 65:3 2006
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tures. The adhesive reliability of a contra-
ceptive patch was shown to be good in sauna
bathing (71).
Conclusions
Human studies on the benecial and adverse
effects of sauna bathing are relatively scarce,
and the study designs are often uncontrolled,
with small subject numbers. Sauna heat has
been administered as either acute, or repeated
exposures. The physiological effects of
eventual habituation to sauna bathing since
childhood have not been studied in depth, in
healthy persons, nor in persons with chronic
diseases.
Based on the present scientic knowledge,
sauna bathing poses no risks to healthy people
from childhood to old age. Even persons with
a cardiac condition may take their sauna baths
safely, if the disease state and medication are
under control. There are new promising Japa-
nese research results on benecial therapeutic
effects of bathing as a part of the treatment
for cardiac failure (2). However, this regimen
has not been repeated in persons accustomed
to bathing. Therefore, further research, with
sound experimental design, is needed before
sauna bathing can be used routinely as a non-
pharmacological treatment regimen in certain
medical disorders.
Acknowledgement
We owe our sincere thanks to Prof. Martin
Halle (Department of Preventive and Rehabil-
itative Sports Medicine, School of Medicine,
Technical University, Munich, Germany) for
his thoughtful comments on our manuscript.
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Katriina Kukkonen-Harjula, D. Med. Sci., Adjunct Prof., Senior Researcher
UKK Institute for Health Promotion Reseach
P.O. Box 30
FI-33501 Tampere, Finland
Email: katriina.kukkonen-harjula@uta.fi
