Relation of Chronotype to Sleep Complaints in the General Finnish Population

Abstract

Individuals show variation in their preference for the daily timing of activities. In this study the authors analyzed whether chronotypes associate with sleep duration and sleep-related complaints. The authors used the National FINRISK Study 2007 Survey data on 3696 women and 3162 men, representative of the Finnish population aged 25 yrs and older, for the assessment of chronotype and self-reported sleep. Evening types experienced insomnia symptoms, had nightmares, and had used recently hypnotics significantly more often than other chronotypes among both men and women. In a multinominal logistic regression model predicting insufficient sleep, the association of eveningness with insufficient sleep was not abolished after adjustment for sex, age, and sleep duration. The prevalence of short sleepers was significantly higher in evening types among men than among women, whereas that of long sleepers was significantly higher in evening types among both men and women, as compared with the other chronotypes. These results indicate that eveningness predisposes individuals to a range of sleep complaints.

Full text

Relation of Chronotype to Sleep Complaints in the General Finnish
Population
Ilona Merikanto,
1,2
Erkki Kronholm,
3
Markku Peltonen,
3
Tiina Laatikainen,
3
Tuuli Lahti,
1,4
and
Timo Partonen
1
1
Department of Mental Health and Substance Abuse Services, National Institute for Health and Welfare, Helsinki, Finland,
2
Department of Biosciences, University of Helsinki, Helsinki, Finland,
3
Department of Chronic Disease Prevention, National
Institute for Health and Welfare, Helsinki, Finland,
4
Department of Behavioural Sciences and Philosophy, Division of Psychology,
Faculty of Social Sciences, University of Turku, Turku, Finland
Individuals show variation in their preference for the daily timing of activities. In this study the authors analyzed
whether chronotypes associate with sleep duration and sleep-related complaints. The authors used the National
FINRISK Study 2007 Survey data on 3696 women and 3162 men, representative of the Finnish population aged
25 yrs and older, for the assessment of chronotype and self-reported sleep. Evening types experienced insomnia
symptoms, had nightmares, and had used recently hypnotics significantly more often than other chronotypes
among both men and women. In a multinominal logistic regression model predicting insufficient sleep, the
association of eveningness with insufficient sleep was not abolished after adjustment for sex, age, and sleep
duration. The prevalence of short sleepers was significantly higher in evening types among men than among
women, whereas that of long sleepers was significantly higher in evening types among both men and women, as
compared with the other chronotypes. These results indicate that eveningness predisposes individuals to a range of
sleep complaints. (Author correspondence: ilona.merikanto@helsinki.fi)
Keywords: Circadian, Eveningness, Hypnotics, Insomnia, Morningness
INTRODUCTION
Differences in diurnalphenotypes are reflectedin variation
of circadian preferences of daily behaviors (Duffy et al.,
1999, 2001; Horne & Östberg, 1976; Roenneberg et al.,
2007; Wyse et al., 2010). In other words, people are
located differentlyat the endsof the morningness-evening-
ness dimension and classified as morning types (M-types)
and evening types (E-types). To our knowledge, so far only
two large epidemiological surveys have been conducted to
estimatethe circadian preference and prevalenceof chron-
otypes. Among the 23 649 individuals (mainly same-sexed
twins ≥24 yrs old) ofthe Finnish Twin Cohort Studyby Kos-
kenvuo et al. (2007), 29.4% considered themselves by a
single question as M-types, 27.7% as “some” M-types,
32.8% as “some” E-types, and 9.7% as E-types. The single
question was derived from the Torsvall-Åkerstedt Diurnal
Type Scale (DTS; Torsvall & Åkerstedt, 1980) that gives
no data on intermediate types (I-types). In a sample of
2526 participants aged 30 to 49 yrs by Paine et al. (2006),
10.2% wer e classified as “definitely” M-types, 39.6%
“moderately” M-types, 44.6% “neither”, 5.0% “moderately”
E-types, and .7% as “definitely” E-types by the Horne-
Östberg Morningness-Eveningness Questionnaire (MEQ;
Horne & Östberg, 1976). Clearly, more generalizable esti-
mates are needed for reliable prevalence rates of diurnal
preference among the general population. Since circadian
preference may influence an individual’s susceptibility to
health and behavioral problems (Levandovski et al.,
2011; Paudel et al., 2011; Prat & Adan, 2011; Taillard
et al., 2001; Urbán et al., 2011), we assessed the prevalence
rates of chronotypes in a representative sample of Finnish
adults, ≥25 yrs of age. In addition, we analyzed the associ-
ations of each chronotype with sleep duration, sleep-
related complaints, and medication.
METHODS
Participants
The National FINRISK Study 2007 Survey was carried out
in six areas of Finland, with 2000 inhabitants, aged 25 to
Address correspondence to Ilona Merikanto, Department of Mental Health and Substance Abuse Services, National Institute for Health and
Welfare, FI-00271 Helsinki, Finland. Tel.: +358 206108213; Fax: +358 206107030; Email: ilona.merikanto@helsinki.fi
Submitted September 15, 2011, Returned for revision October 19, 2011, Accepted December 21, 2011
Chronobiology International, 29(3): 311– 317, (2012)
Copyright © Informa Healthcare USA, Inc.
ISSN 0742-0528 print/1525-6073 online
DOI: 10.3109/07420528.2012.655870
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74 yrs, from each area invited to participate. A random
sample from the Finnish Population Information
System was stratified according to the sex, 10-yr age
groups, and geographical area. Data collection consisted
of a set of self-report questionnaires and a health
examination. Between 22 January 2007 to 30 March
2007, participants of each region were invited to fill in
the questionnaires, which they received beforehand
by mail, and to participate in a health examination,
which was organized in a local health center. Total
participation rate was 67%, and complete data from
3696 women and 3162 men were available for the study
presented here.
Assessment
In the National FINRISK 2007 Study, chronotype was
assessed with six questions derived from the original
19-item MEQ (Horne & Östberg, 1976), which has been
shown to correlate with the intrinsic period of the circa-
dian pacemaker. Shorter circadian periods correlate
with a greater tendency for morningness and higher
sum scores, whereas longer circadian periods correlate
with a greater tendency for eveningness and lower sum
scores (Duffy et al., 1999, 2001). We tested the psycho-
metric properties of our modified questionnaire. The
linear combination of the six items that correlated most
to the original MEQ sum score accounted for 83% of
its total variance (Hätönen et al., 2008). The six-item
Cronbach’s α of .80 indicated their good internal consist-
ency. The mean sum score of the modified scale was 17.8
(SD = 4.2) and the range extended from 5 (extreme even-
ingness) to 27 (extreme morningness). We scaled the
modified cutoff points so that their ranges corresponded
to the original MEQ scaling: definitely or moderately
E-types (5 to 12), I-type (13 to 18), and definitely or mod-
erately M-types (19 to 27).
Sleep wasassessed with the followingfive questions:(1)
“How many hours, on average, do you sleep in one night?”
(in hours); (2) “Do you think you sleep enough?” (Yes,
nearly always; Yes, often; Rarely; I cannot say); (3) “Do
you have nightmares?” (Often; Sometimes; Not at all);
(4) “Do you suffer from insomnia?” (Often; Sometimes;
Not at all); (5) “When was the last time you used sleeping
pills?” (During the past week; 1 week to 1 year ago; Over a
year ago; Never).
Data Analysis
The distributions of chronotypes in relationship to socio-
demographic, socioeconomic, health characteristics
(Table 1), and across sleep variables (Table 2) were
TABLE 1. Sociodemographic, socioeconomic, and health characteristics (%, except for age) of the study
sample across chronotypes in the National FINRISK Study 2007 sample representative of the nationwide
adult general population
Chronotype (N = 6858)
Evening n = 809 Intermediate n = 2807 Morning n = 3242
Sex (R
2
= .004)
Men 41.7 43.3 49.6****
Women 58.3 56.7 50.4****
Age in yrs, mean ± SD (R
2
= .07) 43.3 ± 13.3 47.5 ± 13.9 52.7 ± 13.0****
Marital status (R
2
= .01)
Married or cohabiting 60.9 73.2 74.8****
Single or divorced 37.1 23.8 21.3****
Widowed 2.0 3.0 3.9**
Education (R
2
= .03)
Basic 14.1 17.6 29.6****
Secondary 35.2 34.9 34.5
Higher 50.7 47.5 35.9****
Main occupation (R
2
= .02)
Employee or entrepreneur 63.1 62.5 57.8**
Unemployed 7.3 6.1 5.3*
Retired 15.9 20.6 30.4****
Other 13.7 10.8 6.5**
Self perceived health (R
2
= .01)
Good 51.6 62.1 64.4****
Average 34.7 31.2 30.1*
Bad 13.7 6.7 5.5****
Overexertion or exhaustion (R
2
= .06)
Not at all 31.4 16.0 8.8****
Sometimes 56.9 66.5 64.5****
Often 11.7 17.5 26.7****
Statistical significance for paired comparisons between evening and morning types: *p < .05; **p < .01;
***p < .001; ****p < .0001. R
2
refers to the bivariable explanatory general linear model of the MEQ sum score
as the dependent variable.
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calculated, and the differences between the M-types and
E-types were tested by χ
2
. In order to analyze how insuf-
ficient sleep was related to the chronotype, multinominal
logistic regression models predicting experience of suffi-
cient sleep (reference: always or nearly always) using
chronotype (reference: E-type) as a predictor variable
and sex (reference: men), age, and sleep duration (refer-
ence: 7-h sleep duration) as potential confounding
variables were analyzed (Table 3). A crude model, a
model adjusted for sex and age, and a fully adjusted
model were analyzed. Finally, also a full model with the
interaction terms of chronotype with age and with sex
was analyzed. In addition, crude and adjusted mean
scores on the modified MEQ were calculated across six
sleep-duration groups (Figure 3) using general linear
models (GLMs) adjusted for sex, age, education (basic,
secondary, higher), employment status (employee or
entrepreneur, unemployed, retired, other), marital
status (married or cohabiting, single or divorced,
widowed), self-perceived health status (good, average,
bad), feelings of overexertion or exhaustion (nor at all,
sometimes, often), insomnia symptoms, usage of sleep
medication, nightmares, and insufficient sleep.
Ethics
The National FINRISK Study 2007 Survey was approved
by the Ethics Committee (Institutional Review Board) of
the Hospital District of Helsinki and Uusimaa, Finland
(no. 20.2.2007/229/E0/06) and was conducted according
to accepted international ethical standards (Portaluppi
et al., 2010).
TABLE 2. Characteristics (%) of the study sample across chronotypes
Chronotype
Men (n = 3162) Women (n = 3696)
Evening
(n = 337)
Intermediate
(n = 1216)
Morning
(n = 1609)
Evening
(n = 472)
Intermediate
(n = 1591)
Morning
(n = 1633)
Sleep duration
a
Short (≤ 6 h) sleepers 29.5 19.3 21.3** 18.4 13.5 17.2
7–8 h sleepers 59.6 73.3 73.0**** 69.0 76.2 74.7*
Long (≥9 h) sleepers 10.8 7.4 5.7*** 12.6 10.3 8.1**
Do you think you sleep enough?
a
Yes, nearly always 17.5 31.3 48.4**** 21.2 27.7 45.4****
Yes, often 37.1 46.1 39.3 37.1 49.0 40.3
Rarely 34.7 16.0 6.7**** 32.6 16.5 8.9****
I cannot say 10.7 6.6 5.6*** 9.1 6.9 5.4**
Do you suffer from insomnia?
a
Often 17.8 7.8 5.4**** 19.3 10.4 7.2****
Sometimes 49.6 45.0 39.9** 44.1 49.8 48.1
Not at all 32.6 47.2 54.7**** 36.7 39.7 44.8**
Do you have nightmares?
a
Often 4.5 2.4 2.4* 5.9 4.6 2.6***
Sometimes 48.1 43.0 39.8** 53.4 51.8 45.1**
Not at all 47.5 54.6 57.7*** 40.7 43.6 52.2****
When was the last time you used sleeping pills?
a
During the past week 8.9 4.1 4.7** 9.8 7.1 6.4*
1 wk to 1 yr ago 9.8 5.4 5.2** 12.9 10.0 7.3****
> 1 yr ago 11.9 9.7 7.8* 11.7 10.9 9.1
Never 69.4 80.8 82.3**** 65.7 72.0 77.2****
a
Evening types and morning types are compared with each other across sleep variables in men and women separately.
*p < .05; **p < .01; ***p < .001; ****p < .0001.
TABLE 3. Multinominal logistic regression models predicting experience of sufficient sleep by chronotype
a
Chronotype
(Evening type as a reference)
Sufficient sleep
(Always or nearly always as a reference)
Model 1 OR
(95% CI)
Model 2 OR
(95% CI)
Model 3 OR
(95% CI)
Intermediate Rarely .33 (.26–.41) .37 (.30–.47) .34 (.26 –.44)
Intermediate Often .83 (.68–1.02) .95 (.77–1.17) .87 (.70–1.09)
Intermediate I cannot say .46 (.34–.63) .45 (.33– .62) .42 (.30–.58)
Morning Rarely .10 (.08–.13) .13 (.10– .17) .08 (.06–.11)
Morning Often .44 (.36–.54) .57 (.47–.71) .47 (.38–.59)
Morning I cannot say .25 (.18–.33) .24 (.17–.33) .17 (.12–.23)
a
Model 1 crude (unadjusted); Model 2 adjusted for sex and age; Model 3 adjusted for sex, age, and sleep duration.
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RESULTS
Sex and Age
Sociodemographic, socioeconomic, and health charac-
ters of the study sample across the chronotypes are
described in Table 1. The distribution of chronotypes dif-
fered between me n and women (χ
2
2
= 31.4, p < .0001).
M-types were more frequent (χ
2
1
= 30.7, p < .0001)
among men (51%) than women (44%), whereas E-types
were more frequent (χ
2
1
= 7.3, p = .007) among women
(13%) than men (11%). In both men and women, the
proportion of M-types increased and that of E-types
decreased by age (Figure 1).
Sleep Duration
In the crude analysis, chronotype was associated with
mean sleep duration (F
2
= 3.4, p = .032). I-types slept
slightly more than M-types (7.32 vs. 7.28 h, respectively;
F
1
= 6.8, p < .001), whereas E-types (7.27 h) differed
neither from I-types nor M-types. Adjustment for sex
and age attenuated the effect of chronotype to be non-
significant (F
2
= 2.6, p = .07). The distribution of chrono-
types across sleep-duration groups by sex is shown in
Table 2. Short sleepers were more prevalent among
E-types than M-types in men, but not in wom en.
However, the prevalence of long sleepers was signifi-
cantly higher in E-types than M-types among both
women and men (Figure 2). Figure 3 shows that
among long sleepers there is a clear tendency towards
eveningness (F
5
= 10.7, p < .0001, for the crude means),
which was modulated into a strong linear trend after
the adjustments (F
5
= 29.8, p < .0001, for the adjusted
means).
Insufficient Sleep
The experience of insufficient sleep was more prevalent
among E-types than M-types in the crude analyses
(Table 2). Expectedly, insufficient sleep was associated
FIGURE 1. Prevalence of chronotypes by age. E = evening types;
M = morning types.
FIGURE 2. Prevalence of insufficient sleep by sleep duration and
chronotype among men (A) and women (B).
FIGURE 3. Crude and fully adjusted
†
mean MEQ sum scores
across sleep duration.
†
Adjusted for sex, age, education, work situ-
ation, marital status, self-perceived health, feeling overexerted or
exhausted, insomnia symptoms, use of sleep medication, night-
mares, and insufficient sleep.
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with shorter sleep durations (Figure 2) and older age.
Importantly, the significant association of the E-types
with insufficient sleep was preserved after adjustment
for sex, age, and sleep duration in the multinominal logis-
tic regression model predicting experience of sufficient
sleep (Table 3).
Other Sleep Complaints
E-types reported insomnia symptoms and sleep medi-
cation use significantly more often than M-types
(Table 2). In addition, E-types reported nightmares
more often than M-types (Table 2).
DISCUSSION
Our study revealed two key findings. First, we found that
E-types are more prone to sleep complaints than
M-types, thereby confirming and extending earlier find-
ings (Barclay et al., 2010; Taillard et al., 2001) to the
general adult population. Second, we found the tendency
toward eveningness was more pronounced among long
sleepers than among other sleep-duration groups. Intri-
guingly, multiple adjustments further enhanced this
association, rather than attenuated it.
Sex and Age
Contrary to some earlier studies, we found that evening-
ness was more common among women than men. Roen-
neberg et al. (2007) found men to be more prone to
eveningness than women until the average age of meno-
pause. The results of some other studies are in line with
theirs (Adan & Natale, 2002; Lehnkering & Siegmund,
2007). However, two previous population-based studies
either did not confirm this (Paine et al., 2006) or found
that the relationships between chronotype, sex, and age
to be more complex (Koskenvuo et al., 2007). The discre-
pancy may be due to differences in the recruitment pro-
cesses and the representativeness of the study samples.
The strength of our study is that it constitutes a nation-
wide sample representing the adult general population,
whereas Adan and Natale (2002) assessed university stu-
dents, and Lehnkering and Siegmund (2007) medical
school students, both in locally restricted regions. In
the two previous nationwide surveys, Paine et al. (2006)
assessed persons of a limited age range, and Koskenvuo
et al. (2007) studied a cohort of twins. Roenneberg et al.
(2007) pooled together several samples from different
countries, but did not describe the samples in detail.
Thus, it is impossible to compare our sample with the
other samples.
In our study, morningness was more common and
eveningness less common the older our participants
were. Similar results have been reported also by others
(Koskenvuo et al., 2007; Roenneberg et al., 2007;
Roepke & Duffy, 2010), but a cross-sectional study
cannot verify cause. However, there are several possible
explanations. Individuals may become shifted towards
earlier chronotypes with aging through changes in their
phase relationship between the circadian process and
sleep process, which interact to produce the sleep-wake
cycle and the behavioral trait of diurnal preference. In
particular, the strength of the homeostatic sleep process
to maintain nighttime sleep appears to decrease with
aging, and it may lead to earlier wake-up times (Carrier
et al., 1999; Duffy et al., 1998). Duffy et al. (1998)
suggested that due to the earlier wake-up times, the
increased tendency towards morningness might be
reinforced by earlier light exposures. Moreover, changes
in the circadian process may be related to illnesses that
associate with older age. For instance, patients with
major depressive disorder tend to have a more altered
phase position the more depressed they are (Monteleone
& Maj, 2008; Salgado-Delgado et al., 2011). It is also poss-
ible that the tendency towards eveningness decreases, in
part, due to shorter longevity (earlier age of death) of
E-types, perhaps due to circadian misalignment and
poor sleep increasing the risk of, e.g., cardiovascular dis-
eases (Knutson et al., 2009; Zee & Turek, 2006). Long-
term follow-up studies of the same individuals using
the same assessment methods are needed to clarify
whether these explanations are correct, and additional,
not yet identified, reasons are likely to exist.
Sleep Duration
The average sleep duration did not differ between E-types
and M-types. A similar finding was reported earlier by
Roenneberg et al. (2007). However, the prevalence of
long sleepers was higher among E-types than M-types.
We also found that eveningness was more pronounced
among long sleepers than in other sleep-duration
groups. A new finding was that this association was
further strengthened after adjusting for several sociode-
mographic, socioeconomic, health, and sleep factors. It
suggests that the association between being a long
sleeper and an E-type may reflect a network of effects
due to both physiological and societal components.
Further studies should elucidate this issue.
Our finding of a higher prevalence of short sleepers in
male E-types than M-types is in line with earlier studies,
suggesting that E-types may have shorter sleep durations
during working days than the other chronotypes (Roen-
neberg et al., 2007; Roepke & Duffy, 2010; Soehner
et al., 2011; Taillard et al., 1999). It can result in partial
sleep deprivation, which they may try to compensate
for by sleeping longer on free days. This, in turn, may
delay their circadian rhythms even further, because
E-types tend to be reluctant to advance their bedtimes
(Åkerstedt et al., 2010).
Sleep durations being deviant from population mean
sleep durations have consistently been associated with
the increased risks of morbidity and mortality (Cappucio
et al., 2010, 2011; Gallicchio et al., 2009). These findings
give some support to our hypothesis that the increasing
prevalence of M-types among older age groups may be
partly related to the increased morbidity of E-types.
Paine et al. (2006) did not find an association between
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E-type and “abnormal” sleep duration. However, their
relatively crude scaling of sleep duration may have
masked a possible association (see Kronholm et al.,
2011).
Insufficient Sl eep
E-types reported insufficient sleep more often than
M-types, irrespective of their sleep duration. M-types
have been suggested to have a shorter circadian
period than other chronotypes (Duffy et al., 2001;
Emens et al., 2009). This means that although E-types
tend to wake up at a later clock hour than M-types,
they wake up at an earlier circadian time (Duffy et al.,
1999), closer to their circadian core body temperature
nadir when the circadian drive for sleep is still strong
(Duffy et al., 2001). This tends to result in a greater
experience of sleep inertia and subsequently greater
morning sleepiness levels among E-types, which may
underlie their frequent reports of insufficient sleep.
The higher proneness of E-types to experiencing insuf-
ficient sleep than M-types may be related also to differ-
ences in their homeostatic sleep regulation, probably to
the faster homeostatic sleep pressure dissipation in
M-types (Mongrain & Dumont, 2007; Mongrain et al.,
2005, 2006).
Other Sleep Complaints
E-types were more prone to report insomnia symptoms,
use sleep medication, and experience nightmares than
M-types. These findings are partly in line with earlier
studies. Taillard et al. (2001) reported that both morning-
ness and eveningness were related to chronic insomnia.
Nielsen (2010) reported more frequent nightmares in
E-type than in M-type women. However, the study was
based on an Internet-based questionnaire, making its
findings difficult to compare with ours. Here, we ana-
lyzed the associations of a single insomnia question
with two items of the morningness-eveningness ques-
tionnaire (“Assumi ng adequate environmental con-
ditions, how easy do you find getting up in the
mornings?” and “ During the first half-hour after having
woken in the morning, how tired do you feel?” of which
the latter one gives some information about nonrestora-
tive sleep). We found that there was robust correlation
between the two, so that those who often had the insom-
nia symptom also were more frequently very tired and
less frequently very refreshed during the first half-hour
after having woken in the morning (data not shown).
This association was stronger among E-types than
M-types (data not shown), suggesting that E-types tend
to report insomnia due to non-restorative sle ep.
Limitations
Admittedly, the assessments based on self-reported
information are a limitation of our study. Objective
measures by polysomnography or actigraphy may have
yielded somewhat different results. However, these
methods would have been difficult and expensive to
use because of the large sample size that was distributed
over a large geographical area. It needs to be pointed out
here that we did not have detailed information on the
types of insomnia symptoms (difficulties in initiating
sleep, nocturnal awakenings, early morning awakening,
or nonrestorative sleep) that would have helped us
clarify the association between E-type and insomnia,
and it, therefore, limits the results. Another limitation is
lack of information concerning bedtimes and wake-up
times as well as difference in sleep during working days
and weekends.
On the other hand, the strengths of our study are the
large-sized sample and the good psychometric properties
of the scale we used to assess chronotype. However, the
scores of morningness-eveningness measure a dimen-
sion of diurnal preference, a phenotype, to which a set
of underlying factors contribute. In addition, the current
study is, to our best knowledge, the first report of the dis-
tribution and prevalence of chronotypes in a nationwide
and representative sample of the adult general popu-
lation. Earlier studies have thus far focused on some sub-
groups of the general population, such as twins, university
students, or individuals being of working age, or living in a
particular region of a country.
Declaration of Interest: The authors report no conflicts
of interest. The authors alone are responsible for the
content and writing of the paper.
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Relation of Chronotype to Sleep Complaints 
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