Self-Reported Diurnal Preference and Sleep Disturbance in Type 2 Diabetes Mellitus

Article (PDF Available)inACTA ENDOCRINOLOGICA 2(1):69-82 · January 2011with 60 Reads
DOI: 10.4183/aeb.2011.69
Abstract
Background. Previous sleep studies suggest that type 2 diabetes mellitus is associated with poor quality of sleep and sleep disorders. Aim. To evaluate sleep parameters and diurnal preference in type 2 diabetic patients, using a questionnaire. Methods. Ninety seven patients (aged 55.8±8.3, sex ratio 1:1), previously diagnosed with type 2 diabetes mellitus, together with 102 controls (aged 47.1±10.5, sex ratio 1:1), without diabetes, completed a questionnaire containing the Romanian translation of the Composite Scale of Morningness, the Sleep Disorders Questionnaire, the Pittsburgh Sleep Quality Index, the Pittsburgh Insomnia Rating Scale, the Multidimensional Fatigue Inventory, the Epworth Sleepiness Scale, the Alcohol Use Disorders Identification Test and the Beck Depression Inventory II (BDI). The study was cross-sectional, as we included subjects from outpatient and inpatient facilities. The recruitment process was based on handing invitation letters to patients consulting their physician, as well as to their acquaintances, using the snowball sampling. Participation was voluntary and anonymous. Results. Insomnia was more often reported in diabetic patients: 32 (33.0%) vs. 16 (15.7%) controls, a difference that was highly significant (P<0.001). Diabetic patients used to wake up at approximately the same hour as controls did; nevertheless they went to bed earlier (22:14 ± 0:57 vs. 22:32 ± 1:03), needed more minutes to fall asleep (28.84 ± 21.01 vs. 24.32 ± 23.45) and slept less than controls (7.01 ± 1.56 vs. 7.23 ± 1.18). Statistically significant differences between patients and controls were found regarding the Pittsburgh Sleep Quality Index (P=0.005), the Pittsburgh Insomnia Rating Scale (P<0.001) and the Multidimensional Fatigue Inventory (P=0.001) scores. Eighteen (18.5%) patients also met the criteria for a depressive disorder. No significant differences between patients and controls were found as related to their chronotype (P=0.32) Conclusion. Poor sleep, but not diurnal preference, was linked with the presence of type 2 diabetes mellitus.
Abstract
Background. Previous sleep studies
suggest that type 2 diabetes mellitus is
associated with poor quality of sleep and
sleep disorders.
Aim. To evaluate sleep parameters
and diurnal preference in type 2 diabetic
patients, using a questionnaire.
Methods. Ninety seven patients (aged
55.8±8.3, sex ratio 1:1), previously diagnosed
with type 2 diabetes mellitus, together with
102 controls (aged 47.1±10.5, sex ratio 1:1),
without diabetes, completed a questionnaire
containing the Romanian translation of the
Composite Scale of Morningness, the Sleep
Disorders Questionnaire, the Pittsburgh Sleep
Quality Index, the Pittsburgh Insomnia Rating
Scale, the Multidimensional Fatigue
Inventory, the Epworth Sleepiness Scale, the
Alcohol Use Disorders Identification Test and
the Beck Depression Inventory II (BDI). The
study was cross-sectional, as we included
subjects from outpatient and inpatient
facilities. The recruitment process was based
on handing invitation letters to patients
consulting their physician, as well as to their
acquaintances, using the snowball sampling.
Participation was voluntary and anonymous.
Results. Insomnia was more often
reported in diabetic patients: 32 (33.0%) vs.
16 (15.7%) controls, a difference that was
highly significant (P<0.001). Diabetic
patients used to wake up at approximately
the same hour as controls did; nevertheless
they went to bed earlier (22:14 ± 0:57 vs.
22:32 ± 1:03), needed more minutes to fall
asleep (28.84 ± 21.01 vs. 24.32 ± 23.45) and
slept less than controls (7.01 ± 1.56 vs. 7.23
± 1.18). Statistically significant differences
between patients and controls were found
regarding the Pittsburgh Sleep Quality
Index (P=0.005), the Pittsburgh Insomnia
Rating Scale (P<0.001) and the
Multidimensional Fatigue Inventory
(P=0.001) scores. Eighteen (18.5%) patients
also met the criteria for a depressive
disorder. No significant differences between
patients and controls were found as related
to their chronotype (P=0.32)
Conclusion. Poor sleep, but not
diurnal preference, was linked with the
presence of type 2 diabetes mellitus.
Key words: sleep , insomnia , diurnal
preference , self-reports , circadian rhythms,
type 2 diabetes mellitus.
69
*Correspondence to: Bogdan Voinescu, Babes Bolyai University - Clinical Psychology, Republicii
47 Cluj-Napoca 400015, Romania, Email: bogdan.voinescu@gmail.com
Acta Endocrinologica (Buc), vol. VII, no. 1, p. 69-82, 2011
SELF-REPORTED DIURNAL PREFERENCE AND SLEEP
DISTURBANCE IN TYPE 2 DIABETES MELLITUS
B. Voinescu 1,*, S. Vesa2, A. Coogan3
1“Babes Bolyai” University - Clinical Psychology, Cluj-Napoca, Romania,
Clinical County Hospital of Emergency - Psychiatry, Cluj-Napoca, Romania,
2Emergency Clinical Hospital - Internal Medicine, Cluj-Napoca, Romania
3NUI Maynooth - Psychology, Maynooth, Ireland
Endocrine Care
doi: 10.4183/aeb.2011.69
INTRODUCTION
Considerable epidemiological
evidence shows that life-style changes
impairing sleep have effects on our
circadian rhythms with metabolic
consequences (1, 2). These findings are in
line with increasing evidence
demonstrating that the organization of
metabolism is a key function of circadian
systems (3). Prospective studies from
different geographic regions, that explored
the relationship between sleep duration
and/or quality and diabetes, have indicated
that short or poor sleep may increase the
risk of developing type 2 diabetes, the
association being stronger in women (4).
Among the hypotheses attached to these
observations is that alteration of sleep
homeostasis impacts on metabolism (for
reviews see 1,2) with sleep disorders,
particularly insomnia, appearing to have
important and negative consequences (5-
7). Diabetes itself is also associated with
complications and symptoms, such as
neuropathic pain, nocturia and depression,
that may contribute to sleep disorders,
although sleep disruptions also occur
frequently in diabetic patients without
complications or obesity (1).
Sleep quality and efficacy, as well as
circadian parameters, can be measured
objectively with polysomnography,
actigraphy and endocrine measures, but
these methods are not suitable for all
situations due to their demands on study
participants. Validated self-report
questionnaires assess phenomena that are
currently impossible to measure
objectively with current technologies and
are commonly used, being both
inexpensive and convenient. With no
easily accessible biomarkers of insomnia,
such tools play an important research role
(8). Diurnal preference (i.e. whether a
subject is morning or evening oriented) is
a parameter that is correlated with
biological markers of circadian
rhythmicity, and can be assessed in
subjects by a number of validated
questionnaires, such as the Composite
Scale of Morningness (9).
Purpose of this study
To evaluate sleep parameters and
diurnal preference in type 2 diabetic
patients in a cross-sectional study. We
hypothesized that sleep disruptions are
more severe in patients compared to
controls and that they might be under the
influence of clinical variables and of the
diurnal preference.
SUBJECTS AND METHODS
Participants
Patients were recruited randomly
from outpatient and inpatient facilities at
Baia Mare County Hospital, Romania
from January till July in 2009. All patients
had their diagnosis of type 2 diabetes
mellitus confirmed by a specialist, based
on WHO guidelines. Volunteering control
subjects, aged over 30, were recruited
from patients’ families or acquaintances.
Exclusion criteria were pregnancy
and known co-morbid conditions, such
as cardiac (severe heart failure, unstable
angina), dermatologic (psoriasis),
gastrointestinal (inflammatory bowel
disease), neurologic (stroke, Parkinson
disease, epilepsy, traumatic brain injury),
pulmonary (obstructive sleep apnoea,
persistent asthma, chronic obstructive
pulmonary disease), psychiatric (chronic
B. Voinescu et al.
70
or acute psychosis, bipolar disorder,
dementia, mental retardation), endocrine
(hypo- or hyperthyroidism) diseases. The
study was approved by the Ethics
Committee of “Iuliu Hatieganu”
Medicine and Pharmacy University,
Cluj-Napoca, Romania.
Instruments
A questionnaire containing the
Romanian translation of the Composite
Scale of Morningness (9), the Sleep
Disturbance Questionnaire (10), the
Pittsburgh Insomnia Rating Scale (11), the
Pittsburgh Sleep Quality Index (12), the
Epworth Sleepiness Scale (13), the
Multidimensional Fatigue Inventory (14),
the Alcohol Use Disorders Identification
Test (15) and the Beck Depression
Inventory II (BDI) (16), as well as
demographic and clinical data, were used.
The first three mentioned instruments were
translated and partially validated by
ourselves (17), while the rest have already
been used by other Romanian investigators.
The Composite Scale of Morningness
(CSM) contains 13 questions, most of them
having four choices, with a Likert-type
response format and total scores range
from 13 (extreme eveningness) to 55
(extreme morningness) (9). Although its
authors proposed a three-category
typology, based on the 10th and 90th
percentile, we used the cut-off scores
determined by age groups on the 25th and
75th percentiles that were determined in a
Romanian sample (18).
The Sleep Disturbance Questionnaire
(SDQ) is a self-rating questionnaire with
18 questions on different sleep problems.
The first group of questions asks the
subject to evaluate the presence of
insomnia, excessive sleepiness, sleep
apnoea and parasomnias in the last month.
A subsequent set of questions investigates
the duration, frequency and consequences
of the problem, and is used for the
evaluation of the severity of the sleep
disturbances reported. The SDQ divides
the subjects into three main categories:
subjects who do not complain of any sleep
disorder, subjects who report the
occurrence of insomnia problems without
satisfying the DSM-IV and ICSD criteria
and subjects whose symptoms meet DSM-
IV and ICSD criteria for insomnia (10).
The Pittsburgh Sleep Quality Index
(PSQI) is a widely used, self-rated, 18-
item questionnaire that generates seven
component scores, ranging from subscale
scores 0 to 3: sleep quality, sleep latency,
sleep duration, habitual sleep efficiency,
sleep disturbances, use of sleep
medications and daytime dysfunction.
The global score ranges from 0 to 21; a
higher score is indicative of poorer
subjective sleep quality (12). Used
together with the PSQI, the Epworth
Sleepiness Scale (ESS) is a simple, self-
administered questionnaire that
provides a measurement of the subject’s
general level of daytime sleepiness. It
rates the chances that the subject would
doze off or fall asleep when in eight
different situations commonly
encountered in daily life (13).
The Pittsburgh Insomnia Rating
Scale (PIRS) is a 65-item scale designed
to rate the severity of insomnia in
clinical trials. Subjects rate items that
ask about subjective distress (46 items),
subjective sleep parameters (10 items)
and quality-of-life (9 items) in the past
week. This scale is still under
development, but preliminary data
indicated that the PIRS had good test-
retest reliability as a measure of
Diurnal preference and sleep in diabetes
71
insomnia severity in the past week. It
appeared to have good concurrent
validity with the PSQI (11).
The Multidimensional Fatigue
Inventory (MFI) is a 20-item self-report
instrument designed to measure fatigue. It
covers the following dimensions: general
fatigue, physical fatigue, mental fatigue,
reduced motivation and reduced activity.
General fatigue includes general
statements concerning a person’s
functional state. Physical fatigue refers to
the physical sensation related to the
feeling of tiredness. Possible somatic
symptoms of fatigue such as light-
headedness or muscle pain are not
included in this scale in order to minimize
contamination with symptoms of somatic
illness, independent of fatigue. Cognitive
symptoms such as having difficulties
concentrating are included in the scales
for mental fatigue. Reduced activities and
reduced motivation cover reduction in
activities and lack of motivation to start
any activity (14).
The Alcohol Use Disorders
Identification Test (AUDIT) scale is
one of the brief instruments available
for measuring the prevalence of
hazardous drinking, both in clinical and
student populations. It consists of 10
items. Except for the last two items,
AUDIT questions hint at the previous
year, and responses are weighted
between 0 and 4, generally based on
frequency of occurrence (19).
The Beck Depression Inventory II
is a widely used instrument for
measuring the severity of depression. It
is composed of 21 items relating to
symptoms of depression, each of which
consists of four self-evaluative
statements scored 0 to 3. Responses are
summed to yield a total score that
ranges from 0 to 63 (16).
Procedure
Participation was voluntary and
anonymous. Diabetic patients, not
meeting the exclusion criteria, received
an invitation letter from their GP or
specialist. The letter explained the
nature of research and ethical
requirements for confidentiality. If
agreed, they were given the
questionnaires to be completed. All the
participants were also asked to further
recruit adult participants from their
acquaintances using the snowball
sampling. Completing the survey was
considered implied consent to
participate in this study. We did not
count how many questionnaires had
been handed.
Statistical analysis
Total scores are expressed as
means, standard deviations, medians
and 25 and 75 percentiles. Distribution
shapes were assessed for normality with
the Kolmogorov–Smirnov test. The
reliability of the scales was estimated by
Cronbach’s αcoefficients. To examine
the statistical significance of the
differences, the Mann-Whitney U test
was used. To evaluate the distribution of
various characteristics, Chi Square test
was used. Kendall’s tau b was used for
calculating correlations between the
different variables. A P value, lower
than 0.05, was considered significant.
Data analysis was performed using the
SPSS (version 16.0.2).
RESULTS
Descriptive statistics
Ninety seven patients and one
hundred and two controls were selected
B. Voinescu et al.
72
for this study. About half of the patients
were men (N=49; 50.5%). Most of the
controls were women (N=53; 52.0%).
Controls were younger than patients:
mean age was 55.85±8.30 in the patients’
sample and 47.16±10.53 in the controls’
one. Five subjects did not fill their ages.
Age was not normally distributed and the
difference between the groups was highly
significant (P<0.001).
The mean body mass index (BMI) in
the patients group was 30.21±6.24 and
25.49±4.44 in the control group. Six
subjects did not fill their height and weight,
therefore BMI was not calculated. This
difference in BMI between the diabetic and
control groups was highly significant
(P<0.001). About half of the patients (43;
47.7%) were obese (BMI 30) compared
to eleven (10.9%) of the controls, and this
difference was highly significant (Chi
square test, P<0.001). Neither neuropathy,
nor peripheral arterial disease was reported
by the selected individuals.
The majority of diabetic patients
complained of insomnia: 55 (56.7%) as a
symptom, while 32 (33.0%) fulfilled the
criteria of insomnia as a disease. Controls
had less primary sleep disturbance, with
65 (63.7%) of controls displaying
insomnia symptoms, but only 16 (15.7%)
insomnia as a disease. Ten patients
(10.3%) and 21 (20.6%) controls had no
insomnia complaints at all. These
differences were highly significant (Chi
square test, P<0.001). We found no
important differences in alcohol use or
smoking before going to sleep, as well as
in snoring, breathing difficulties or pain
during the night (details of the above in
Table 1). However, patients had nocturia
significantly more frequently (P=0.026).
Diurnal preference and sleep in diabetes
73
Diabetes Controls
Age* (years) 55.85±8.30 47.16±10.53
BMI* 30.21±6.24 25.49±4.44
BMI percentile
25th 25.88 22.06
50th 29.75 25.15
75th 32.96 28.01
Obesity (BMI >30 kg/m2) (%) 46.7 10.9
Sex (% male) 50.5 48.0
Current smoker (%) 23.3 25.5
Current alcohol consumption** (%) 38.5 20.2
Snoring (%) 36.7 28.4
Breathing problems (%) 11.3 7.8
Depression (%) 18.5 0
Sleep difficulty (%)
Normal sleeping 10.3 20.6
Poor sleeping 56.7 63.7
Insomnia 33.0 15.7
Table 1. Demographic, clinical, and sleep characteristics of the study population
* means and standard deviations
** moderate and high consumption as revealed by AUDIT
About half of the patients (49) were
using insulin for the treatment of their
disease. We found that they had
significantly more frequent sleep
disturbances (P=0.032) and obesity
(P=0.02) compared to those patients who
were not using insulin.
Psychometric Scales
A summary of the median scores
in the used scales, together with 25th
and 75th percentiles, range, α
Cronbach’s coefficients and P values in
the Mann-Whitney U-test are presented
in Table 2.
Pittsburgh Sleep Quality Index
Diabetic patients reported fairly
similar waking up times as controls did,
but they went to bed earlier, needed
more minutes to fall asleep, slept less
and spent more hours in bed, as it can be
seen in Table 3.
Patients complained of significantly
more severe sleep disruptions (P=0.03),
reported more time to fall asleep
(P=0.009), had a less efficient sleep
(P=0.007) and of a poorer quality
(P=0.03); they also used sleep
medications more frequently than controls
(P=0.001). Obesity was not significantly
associated with PSQI scores higher than
5, as obese and non-obese patients were
almost equally distributed.
Among other differences between
the groups, diabetic patients complained
significantly more often of feeling too
warm or cold during the night and of
nocturia, but not of pains, as revealed in
Table 4.
Sixty seven (69.1%) patients
scored higher than 5, the cut-off score
for bad sleepers. Twenty three (44.2%)
of them had insomnia as a disease and
twenty nine (55.8%) insomnia as a
symptom. Male patients reported worse
sleep quality than women, but the
differences were not significant.
Patients with insomnia as a disease
scored higher than those with insomnia
as a symptom and the difference was
significant (P=0.066). Thirty five
controls (34.3%) scored higher than 5 in
PSQI. Twenty one (20.6%) had no
insomnia complaints, while 65 (63.7%)
had insomnia symptoms and 16 (15.7%)
insomnia as a disease.
Pittsburgh Insomnia Rating Scale
Diabetic patients scored
significantly higher in this scale and its
subscales, reflecting that they reported
more severe sleep disruptions and worse
quality of life (see Table 5). The PIRS
scores were highly significantly related
to the total PSQI ones (τ=0.335,
P<0.001). The PIRS subscales were
highly significantly related to the total
PSQI scores, particularly the Sleep
Parameters (τ=0.424, P<0.001) and the
Quality of Life one (τ=0.396, P<0.001).
Multidimensional Fatigue Inventory
Patients displayed higher levels of
fatigue and significant differences in
mental and activity subscales (as seen in
Table 5). MFI scores were lowly
correlated with the PSQI (τ=0.192,
P<0.001) and correlated with a medium
strength with PIRS (τ=0.329, P<0.001).
Epworth Sleepiness Scale
Diabetic patients complained
slightly more often of daytime
sleepiness, but the significance did not
reach the 0.05 level. Twenty six
(29.21%) of the patients scored higher
than 10, compared to 21 (24.13%) of the
B. Voinescu et al.
74
Diurnal preference and sleep in diabetes
75
Table 2. Summary of the descriptive statistics and reliability for the scales used
(αCronbach is calculated for the whole sample). Last column is for the P values
in Mann-Whitney U test (significant values are in bold)
controls and this difference was not
significant. Scores in ESS were either
not significantly, or poorly, correlated
with the other scales: τ=0.061(P=0.13)
with PSQI, τ=0.136 (P=0.005) with
PIRS, τ=0.076 (P=0.077) with MFI.
Beck Depression Inventory II
From the subjects that completed the
BDI, patients did score higher than the
controls and the differences were
significant. Eighteen (18.5%) patients met
the criteria for current depressive disorder.
According to BDI cut-off scores, 7 (7.2%)
of the patients had severe depression,
while 8 (8.24%) had moderate one.
Compared to controls, the differences
were highly significant (P<0.001). The
BDI scores were highly significantly
related to the PIRS ones (τ=0.472,
P<0.001) and PSQI (τ=0.327, P=0.001),
and poorly to the Epworth (τ=0.206,
P=0.005) and the MFI ones (τ=0.180,
B. Voinescu et al.
76
Table 3. Means and SDs for sleep parameters in patients and controls
PSQI Parameter Patients Controls
Waking Up Time 6:35±0:59 6:35±1:25
Going to Bed Time 22:14±0:57 22:32±1:03
Minutes Needed for Falling
Asleep
28.84±21.01 24.32±23.45
Hours of Sleep 7.01±1.56 7.23±1.18
Hours Spent in Bed 8.35±1.30 7.74±1.25
Table 4. Sleep difficulties and their frequency; last column is the Pearson Chi-Square
Frequency Patients Controls P
Had to use the
bathroom
Not during the past month 13 16
Less than once a week 11 25
Once or twice a week 26 25 0.026
Three or more times a week 40 25
Felt too cold Not during the past month 58 72
Less than once a week 19 10
Once or twice a week 3 9 0.001
Three or more times a week 10 0
Felt too hot Not during the past month 42 61
Less than once a week 16 15
Once or twice a week 14 10 0.009
Three or more times a week 18 5
Had pains Not during the past month 44 57
Less than once a week 15 13
Once or twice a week 18 9 0.183
Three or more times a week 13 12
P=0.016). Of the patients who completed
the scale, only one (2.85%) had no
insomnia symptoms and 24 (68.5%) were
bad sleepers according to PSQI.
Alcohol Use Disorders Identification Test
In this scale, the patients did score
higher than the controls again; however,
the differences were not significant. The
AUDIT scores were significantly, but
poorly related to the PIRS (τ = 0.115,
P=0.045), the MFI (τ = 0.226, P<0.001)
and the Epworth ones (τ = 0.230,
P<0.001). No association between
chronotype, insomnia accuses or severity
of depression (according to BDI) and
alcohol consumption were found, but we
did find one between bad sleepers
(according to PSQI) (P<0.001).
Composite Scale of Morningness
The median of the total CSM score
for the patients group was 41, in both
men and women; in controls median
was 43 in men and 39 in women. CSM
scores did not correlate to the other
variables. There were no significant
differences between those affected by
diabetes and those unaffected in their
diurnal preference (P=0.32). Although
evening types appeared to be bad
sleepers more frequently, no difference
was found in the distribution, using the
percentiles rules (P=0.826). Morning
types complained of slightly more
fatigue, but the differences were not
significant. Most of the patients that had
depression (N=15; 45.45%) were of the
evening type and the difference was
significant (P=0.011).
DISCUSSION
This study attempts to assess both
the quality of sleep and the consequences
of loss of sleep in diabetic patients
compared to controls and to explore the
relationship between diurnal preference
and type 2 diabetes mellitus. About two
hundred participants were selected for
Diurnal preference and sleep in diabetes
77
Table 5. Medians and 25/75 percentiles for the scores in PIRS and MFI subscales in
patients and controls, together with Mann-Whitney U-test results
Patients Controls P
Percentile 25 50 75 25 50 75
PIRS
Sleep distress 44 61 76 13.5 34 56.5 <0.001
Sleep parameters 7 9 12 3 7 10 <0.001
Quality of life 9 12 14 7 9 12 0.001
MFI
General fatigue 10 12 14 9 11 13 0.180
Activity fatigue 10 11 14 7 10 13 0.013
Physical fatigue 8 11 14 8.75 10.5 13 0.274
Motivation fatigue 8 10 12 6 8.5 12 0.077
Mental fatigue 9.5 11 13 6.75 9.5 12 0.004
this research and were self-assessed with
validated translated instruments that
displayed similar psychometric properties
to the original ones. Sex distribution was
almost similar among the two compared
groups, but the patients’ group was older.
The sleep-wake cycle is one of the
most obvious patterns in human
behavior and physiology and it is
believed to be intimately involved in the
onset and during the course of diabetes
(1, 2, 5-7, 20-22). Moreover, shift work
or fragmented working hours have been
associated with increased risk for
obesity, diabetes, and cardiovascular
disease, with recent results showing that
in healthy people, irregular sleep
patterns could increase the risk of
developing diabetes (23). Although
obesity was more often found in the
diabetics’ group, it appeared to have a
minor influence on the sleep pattern.
Sleep disorders, particularly
insomnia, appear to have important and
negative consequences (5-7, 24). In our
study, insomnia as a disease was
significantly more frequent among the
diabetics, as about a third of them
complained of it, while insomnia
symptoms were fairly equally reported.
As the data collected by the PSQI showed,
there were hardly any differences in the
sleep parameters (such as going out/to bed
times, duration, latency), but patients
suffered from less efficient and more
disturbed sleep, and chose to use
hypnotics more often. Nocturia, feeling
too cold or too warm were the main
reasons for disturbed sleep. Nocturnal
pains were fairly similar among the
groups, although neuropathic pain is quite
an often complication of the diabetes. The
PIRS confirmed much of the PSQI results,
as patients again scored significantly
higher than controls, this meaning that
insomnia was less severe in the second
group. Not surprisingly, sleep loss had
more profound effects in the first group,
with daytime sleepiness and fatigue
affecting the individual particularly in the
mental and motivational fields. Although
there is consistent data pointing out that
long or short sleep duration associate with
diabetes (2, 22, 25, 26), and sleep duration
was described as a strong predictor of
glucose control through HbA1c (2), we
report no differences between patients and
controls in the current study.
There are now many indications
that the circadian clock plays a major
role in the development of type 2
diabetes (27-30). To our knowledge it is
the first time when diurnal preference
was assessed in diabetic patients as a
marker of the circadian timing. It has
been reported that evening types
suffered psychiatric disease more
commonly than intermediates or
morning-oriented individuals (31-33)
and are more prone to substance misuse
(34-36); we did find a significant link of
the evening type with depression, too.
As related to any of the other variables
under investigation in the present study,
we report no significant association
with diurnal preference, but this could
be due to the sample size and the way
data was collected. Still, associating
behaviors with biological circadian
phase markers, such as melatonin and
core body temperature (37), genetic
polymorphisms of clock genes (38) or
RNA profiling (39) may in the future
provide deeper insight into the
interaction of circadian timing and type
2 diabetes, as well as other endocrine
B. Voinescu et al.
78
disorders (40).
Study Limitations
As controls were not screened for
impaired glucose tolerance, some cases
of diabetes may have been undiagnosed.
Glucose control was not monitored. Sleep
and sleep loss consequences were self-
assessed with psychological instruments
that are not as reliable as objective
measurements. Therefore, there could be
over- or underestimations of the assessed
variables. Moreover, we did not ascertain
if insomnia appeared independently or as
a consequence of diabetes.
CONCLUSION
Poor sleep, but not diurnal
preference is linked with the presence of
type 2 diabetes mellitus.
Acknowledgements
We would like to thank to the
physicians who referred the patients to the
research, particularly to Dr. Mihaela
Mociran, Dr. Lavinia Pop (both
Diabetologists in Baia Mare), Dr. Felicia
Borz, Dr. Ligia Fanea, Dr. Cornelica Ilea,
Dr. Erzsebet Hidegcuti, Dr. Coralia
Ubelhart (all of them General Practitioners
in Baia Mare), and all the participants taking
part in the research, who kindly devoted
considerable amount of their time to be
tested and provide the data.
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