Work-related Sleep disturbance
Work-Related Sleep Disturbances and Sickness Absence in the Swedish
Working Population, 1993-1999
Hugo Westerlund, PhD1; Kristina Alexanderson, PhD2; Torbjörn Åkerstedt, PhD1; Linda Magnusson Hanson, PhD1; Töres Theorell, MD, PhD1;
Mika Kivimäki, PhD3
Stress Research Institute, Stockholm University, Stockholm, Sweden; 2Section of Personal Injury Prevention, Department of Clinical Neuroscience,
Karolinska Institute, Stockholm, Sweden; 3Department of Epidemiology and Public Health, University College London, London, UK
1
Study Objectives: To examine secular trends in work-related sleep
disturbances and their association with sickness absence in the Swedish working population.
Design. Nationally representative cross-sectional samples of the Swedish working population aged 16-64 (the biennial Swedish Work Environment Survey) in 1993, 1995, and 1999 respectively. Questionnaire data
on work-related sleep disturbances were linked to records of medicallycertified sick-leave spells exceeding 14 days obtained from national
registers.
Setting: All Sweden.
Participants: A total of 28,424 individuals aged 16-65 with complete data (5162/5173 women/men in 1993; 4635/4764 in 1995; and
4422/4268 in 1999).
Interventions: N/A.
Measurements and Results: The age-adjusted proportion of women
with work-related sleep disturbances at least once a week increased
from 12.3% in 1993 to 21.7% in 1999 (P < 0.001). The corresponding
figures for men were 12.5% to 18.6% (P < 0.001). There was a strong
cross-sectional association between work-related sleep disturbances
and sickness absence in both genders and in each studied year. Using
binary logistic regressions and adjusting for age, supervisory position,
and geographical region, the odds ratios for sickness absence for those
who reported work-related sleep disturbances every day, compared with
those who answered “not at all/seldom last 3 months” varied between
3.22 (1.88-5.50) and 4.26 (2.56-7.19), with the strongest associations
seen in 1999. Adjustment for health indicators, especially depressive
symptoms, attenuated the relationship substantially.
Conclusions: Self-reported sleep disturbances attributed to workrelated causes were on the rise in Sweden and were associated with
medically-certified sickness absence. Most of this association seems to
be accounted for by depressive symptoms.
Keywords: sleep disturbances, sleep, secular trend, sickness absence, gender, work, depressive symptoms
Citation: Westerlund H; Alexanderson K; Åkerstedt T; Hanson LM;
Theorell T; Kivimäki M. Work-related sleep disturbances and sickness absence in the swedish working population, 1993-1999. SLEEP
2008;31(8):1169-1177.
SLEEP HAS FAR-REACHING EFFECTS ON ENDOCRINOLOGY, IMMUNOLOGY, AND METABOLISM.1 SEVERAL STUDIES HAVE SHOWN SLEEP DISTURBANCES
to be associated with increased risk of health problems2-9 and,
in working populations, with increased sickness absence,10-14
which in turn has been suggested as an integrated measure of
physical, psychological, and social functioning.15 The etiology
behind sleep disturbances can vary, and sleep disturbances can
be symptoms of disease as well as risk factors for ill health.
Work stress and poor working conditions have been shown to
be associated with sleep disturbances16-19 and increased need for
recovery.7 In a survey in the USA, the most frequent self-reported cause of sleeping difficulties was work-related stress.20 Sleep
disturbances may indeed be a mediator between work-related
factors and sickness absence.
Population-based evidence on secular trends in sleep disturbances is scarce. A Swedish study reported a sharp increase in
prevalence of sleep disturbances from 1996/1997 to 2002/2003
among both women and men,21 and corresponding findings
have been reported in 2 other Scandinavian studies.22,23 A recent
Finnish study showed a minor decrease in self-reported sleep
duration from 1972 to 2005 and presented tentative evidence
for an increase in insomnia-related problems in the working
age population during the last 10 years.24 However, some commentators argue that there is no firm evidence of an increase in
sleep debt over the years.25 Regarding sickness absence, a substantial increase in sick leaves due to mental disorders has been
reported in several countries in the last decades.26-30 A Swedish
study reported a parallel rise in fatigue and sick-leave days between 1994 and 2002, and an increased prevalence of fatigue
and anxiety among younger people with a high number of sickleave days.31 Nevertheless, little is known about the association
between sleep disturbances and sickness absence, of possible
changes in this over time, or about the extent to which sickness
absence is attributable to work-related sleep disturbances.10
Most of the existing studies are cross-sectional,11-13,32 or focus
on fatigue in specific trades.7 We are not aware of any previous population-based studies that investigate the association
between work-related sleep disturbances and sickness absence
over time.
The aim of the present study was to examine secular trends in
work-related sleep disturbances; the association between work-
Disclosure Statement
This was not an industry supported study. Dr. Åkerstedt has participated
in a speaking engagement for Sanofi-Aventis. The other authors have indicated no financial conflicts of interest.
Submitted for publication June, 2007
Accepted for publication May, 2008
Address correspondence to: Dr. Hugo Westerlund, Stress Research Institute at Stockholm University, S-106 91 Stockholm, Sweden; Tel: +46-85537 8926; Cell: +46-76-814 1011; Fax: +46-8-5537 8900; E-mail: hugo.
[email protected]
SLEEP, Vol. 31, No. 8, 2008
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Sleep Disturbances and Sickness Absence 1993-1999—Westerlund et al
Sickness Absence
related sleep disturbances and long-term sickness absence; and
changes in this association over 8 years in the Swedish working
population.
All employed residents in Sweden are covered by sickness
insurance entitling them to compensation for work incapacity
due to disease or injury. Self-certification for sick-leave was
accepted for the first 7 calendar days of a spell; thereafter a
sickness certificate from a physician was required.
It has been argued that gender differences in sickness absence are due to women taking sick-leave in order to care for
(sick) children. In Sweden this has probably not been the case,
as the parental insurance is generous. In the years studied here,
it covered absence from work to care for newborn (450 days) or
sick (60 days/year/child) children. Data on this type of absence
were not included.
We obtained records of sickness absence from the Income
and Capital Register (IoF). These records were linked to SWES
and LFS data through unique personal identification numbers.
In 1993, 1995, and 1999, the public social insurance office
started paying sickness benefit on the 15th day of a sick-leave
spell, since the the first 14 days of each spell were paid by the
employer. Therefore, public registeres contain information only
about sick-leave spells exceeding 14 days. For all these absences a physician’s certificate was required. Since sickness absence
was registered somewhat differently in 1997, that year was not
included in the cross-sectional analyses. We contrasted people
who had at least one sick-leave spell exceeding 14 days with
those who had no such spell.
METHODS
We performed cross-sectional and time trend analyses in
the Swedish working population linking questionnaire data on
work-related sleep disturbances to register data on medically
certified sick-leave spells exceeding 14 days.
Study Sample
Participants were all respondents of the biennial Swedish
Work Environment Survey (SWES), comprising representative samples of the Swedish working population aged 16-64.33
These samples are derived from the respondents in the annual
national Labour Force Survey (LFS). The sampling method is
stratified on geographic region, sex, citizenship, and employment. Our analysis included 3 steps, each of which had specific
inclusion criteria:
Included in the descriptive part of the present study were
participants in SWES in any of the years 1993, 1995, 1997, or
1999. There were a total of 41,912 participants with complete
data on work-related sleep disturbances, ranging from 9,608 to
11,476 in each survey, corresponding to between 77.0% and
86.5% of the original samples (average 81.2%).
In the analyses of cross-sectional associations between
work-related sleep disturbances and sickness absence, only
subjects participating in the 1993, 1995, and 1999 SWES were
included, since the rules for sickness absence benefits and registration were comparable those years. Of the initial 38,897
persons in the database for those 3 years, we excluded those
who did not respond to the question about work-related sleep
disturbances (n = 7,190), subjects who had received unemployment benefit during the year in question (n = 2,991), and subjects with incomplete data on supervisory position or county
of employment (n = 302). A total of 28,424 subjects were thus
used in the analyses of association between work-related sleep
disturbances and sickness absence, corresponding to 73.1% of
the total original samples for the 3 years.
In the analyses of possible explanatory factors for the association between sleep disturbances and sickness absence, another
4,851 were excluded because of missing data on one or more
of the covariates. (i.e., psychosocial work environment, hospitalizations, and self-reported health problems). Thus, a total of
23,573 subjects were included in these analyses.
Adjustment Variables
Data on age, sex, county of employment, and unemployment
benefit were obtained from Statistics Sweden. Regional (county) levels of sickness absence in relation to national mean were
obtained from the Swedish Social Insurance Agency. Counties
were defined as being above or below the national mean. Data
on whether the participants had a supervisory position or not
were taken from the LFS telephone interviews. Work environment was measured by proxies of psychological demands, decision authority, skill discretion, and social support, as in previous
studies.34 Self-reported symptoms were measured by questions
(cf. Appendix) regarding depressive symptoms (2 items), physical exhaustion after work, psychosomatic symptoms (2 items),
and musculoskeletal symptoms (6 items). Although our measure
of depressive symptoms includes tiredness and listlessness, it
was only weakly correlated with work-related sleep disturbances
(Spearman rho 0.34). Hospital admission data were obtained from
Centre for Epidemiology, Swedish National Board of Health and
Welfare, and were dichotomized into none versus any number of
admissions during the survey year.
Sleep Disturbances
Statistical Methods
Work-related sleep disturbances were measured by one question in the self-completion questionnaire that is sent to the participants in the SWES: In the past three months how often have
you had difficulties sleeping because thoughts about work have
kept you awake? The response options were: “Every day”; “A
couple of days a week (1 day of 2)”; “One day a week (1 day
of 5)”; “A couple of days a month (1 day of 10)”; “Not at all/
Seldom in the last 3 months.”
SLEEP, Vol. 31, No. 8, 2008
Time trends in work-related sleep disturbances were analyzed
with Kruskal-Wallis H Test. In order to adjust for the potential
inflation of the overall type I error rate, we used the Bonferroni
method for post hoc testing of pairwise differences between
years. Direct age adjustment was made with 5-year strata, with
the 1993 through 1999 samples combined as norm. ANCOVA
was used to test differences in psychosocial work environment
1170
Sleep Disturbances and Sickness Absence 1993-1999—Westerlund et al
50
50
45
45
40
35
22.4
30
25
20
5
6.7
4.5
0
93
1.1
6.7
10.1
9.0
8.3
95
2.1
97
One day a week
30
A couple of days a
month
35
25
20
20.3
20.1
20.7
7.7
8.4
15
Every day
9.3
7.0
1.2
40
A couple of days
a week
19.2
15
10
20.9
20.6
A couple of days a
month
2.4
10
7.0
5
4.2
0
99
93
1.4
6.1
95
1.2
5.7
97
One day a week
20.8
A couple of days
a week
Every day
9.6
7.2
1.4
1.8
99
Figure 1—Age-adjusted prevalence of work-related sleep disturbances in the past 3 months among the women in stratified, random samples of the Swedish working population 1993–1999.
Figure 2—Age-adjusted prevalence of work-related sleep disturbances in the past 3 months among the men in stratified, random
samples of the Swedish working population 1993–1999.
between the years, adjusting for age. Cross-sectional associations between work-related sleep disturbances and sickness absence, adjusting for age, supervisor position, and region were
analyzed with binary logistic regression analyses, stratified by
sex, in 1993, 1995, and 1999 respectively. Further adjustments
were made for psychosocial work environment and health indicators in models containing all 3 years, with year as an adjustment variable. To test whether the strength of the association
between work-related sleep disturbances and sickness absence
varied by year, we added the interaction term “work-related
sleep disturbances × study year” in a regression model already
containing the main effects. The 95% confidence intervals (CI)
for odds ratios (OR) were calculated. Statistical analyses were
conducted using SPSS for Windows, versions 15.0 and 16.0.
each year are shown in Table 2. There was no significant change
in sickness absences over time for either sex, or in the one-year
prevalence of hospital admissions. However, self-rated psychosocial work environment deteriorated over time, and there
was an increase in self-reported health problems (all trends P <
0.001).
Tables 3 and 4 show strong and significant associations between self-rated work-related sleep disturbances and the likelihood of having at least one recorded sick-leave spell exceeding
14 days. The association was found in both men and women,
and there was a tendency towards a dose-response relationship, with the by far the highest risk of having at least one long
sick-leave spell among those who reported having work-related
sleep disturbances every day. The associations were virtually
unchanged after adjustment for supervisory position and regional level of sickness absence. Although the prevalence of
sickness absence was much higher in women than in men, the
strength of the associations between work-related sleep disturbances and sickness absence was almost the same for women
and men (P for gender difference 0.70). In women but not in
men, however, there was a strengthening of the association over
the years (P = 0.008).
In further analyses we added proxies for stressful work environment and health in regression models with all years analyzed
together (Table 5). Skill discretion in both sexes, and psychological demands and decision authority in women, were associated
with risk of sickness absence, in the expected directions. However, inclusion of psychosocial work environment measures in the
model only marginally affected the associations between workrelated sleep disturbances and sickness absence. In contrast, inclusion of health measures as a block substantially attenuated the
relationship, leaving only work-related sleep disturbances every
day significantly associated with sickness absence. Among the
health measures, the strongest individual predictor of sickness
absence in the mutually adjusted model was hospital admission
(OR = 13.5 [11.5–15.9] in women and 11.8 [9.75–14.2] in men),
which, however, did not explain any of the association between
work-related sleep disturbances and sickness absence (Table 6).
Instead, adjustment for depressive symptoms reduced the esti-
Ethics
We obtained ethics approval for the study from the Regional
Research Ethics Board as well as from the research ethics committee at Statistics Sweden.
RESULTS
Work-related sleep disturbances increased markedly in the
Swedish working population during 1993–1999, especially among women, (Figure 1 and 2 [trend P < 0.001 for both
sexes]). This increase was statistically significant between all
consecutive pairs of years for both sexes (P < 0.01 for pairwise
comparisons). The age-adjusted proportion of women with
work-related sleep disturbances at least once a week was 12.3%
in 1993 and 21.7% in 1999; the corresponding figures for men
were 12.5% and 18.6%, respectively.
Table 1 shows background characteristics for the participants
with complete data for the analyses of cross-sectional associations. Comparable cross-sectional data on sickness absence
are available for the participants in the 1993, 1995, and 1999
SWES. The age-adjusted one-year prevalence of sick-leave
spells exceeding 14 days, hospitalizations, self-reported health
problems, and indicators of psychosocial work environment in
SLEEP, Vol. 31, No. 8, 2008
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Sleep Disturbances and Sickness Absence 1993-1999—Westerlund et al
Table 1—Descriptive Statistics for Those Participants in the SWES Populations Who had Complete Data on All Variables Used in the Analyses of Cross-Sectional Associations* and Who had not Received Unemployment Benefit. Values are Numbers (Percentages of the Sample).
Women
1993
1995
1999
1993
n (%)
n (%)
n (%)
n (%)
Total number of respondents 5162 (100)
4635 (100)
4422 (100)
5173 (100)
Age
16–20
155 ( 3.0)
123 ( 2.7)
125 ( 2.8)
97 ( 1.9)
21–25
327 ( 6.3)
263 ( 5.7)
213 ( 4.8)
346 ( 6.7)
26–30
536 (10.4)
460 ( 9.9)
388 ( 8.8)
588 (11.4)
31–35
595 (11.5)
489 (10.6)
520 (11.8)
617 (11.9)
36–40
667 (12.9)
620 (13.4)
556 (12.6)
693 (13.4)
41–45
792 (15.3)
665 (14.3)
593 (13.4)
754 (14.6)
46–50
826 (16.0)
752 (16.2)
657 (14.9)
816 (15.8)
51–55
618 (12.0)
641 (13.8)
710 (16.1)
607 (11.7)
56–60
449 ( 8.7)
425 ( 9.2)
493 (11.1)
439 ( 8.5)
61–65
197 ( 3.8)
197 (4.3)
167 ( 3.8)
216 ( 4.2)
Employment position
supervisor
1250 (24.2)
1159 (25.0)
1142 (25.8)
1943 (37.6)
non-supervisor
3912 (75.8)
3476 (75.0)
3280 (74.2)
3230 (62.4)
Level of sickness absence in 2002 in the county where the subjects worked
below national mean
3211 (62.2)
2930 (63.2)
2874 (65.0)
3181 (61.5)
above national mean
1951 (37.8)
1705 (36.8)
1548 (35.0)
1992 (38.5)
Sick-leave spells >14 consecutive days
No
4290 (83.1)
3843 (82.9)
3650 (82.5)
4626 (89.4)
Yes
872 (16.9)
792 (17.1)
772 (17.5)
547 (10.6)
Men
1995
n (%)
4764 (100)
1999
n (%)
4268 (100)
104 ( 2.2)
320 ( 6.7)
565 (11.9)
553 (11.6)
572 (12.0)
651 (13.7)
751 (15.8)
643 (13.5)
411 ( 8.6)
194 ( 4.1)
100 ( 2.3)
265 ( 6.2)
455 (10.7)
558 (13.1)
531 (12.4)
532 (12.5)
573 (13.4)
620 (14.5)
450 (10.5)
184 ( 4.3)
1858 (39.0)
2906 (61.0)
1563 (36.6)
2705 (63.4)
2912 (61.1)
1852 (38.9)
2675 (62.7)
1593 (37.3)
4292 (90.1)
472 ( 9.9)
3829 (89.7)
439 (10.3)
*Work-related sleep disturbances, sickness absence, age, supervisory position, and region.
Table 2—Age-Adjusted One-Year Prevalence of Sick-Leave Spells Longer than 14 Days, and Hospital Admission, Plus Mean Values for
Self-Rated Psychosocial Work Environment and Health Measures, in 1993, 1995, and 1999.*
Work-related sleep disturbances at least
once a week in the last 3 months**
Sick-leave spells > 14 days
Hospital admission (any cause)
Psychological demands at work (0–10)
Decision authority (0–10)
Skill discretion (0–10)
Social support (0–10)
Depressive symptoms (0–4)
Physical exhaustion (0–4)
Psychosomatic symptoms (0–4)
Musculoskeletal symptoms (0–4)
1993
1995
12.6%
16.9%
8.1%
2.95
5.53
5.76
7.47
0.82
1.33
0.83
0.89
15.5%
16.6%
7.7%
3.10
5.51
5.49
7.38
0.95
1.47
0.92
0.94
Women
1999
22.7%
16.3%
6.9%
3.52
5.27
5.47
7.20
1.13
1.57
1.07
1.06
P for trend
1993
1995
< 0.001
0.914
0.138
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
12.3%
10.1%
5.2%
2.91
6.47
6.07
6.53
0.76
1.25
0.66
0.62
15.1%
9.4%
4.9%
3.00
6.32
5.86
6.62
0.85
1.31
0.76
0.68
Men
1999
18.8%
9.5%
4.7%
3.13
6.05
5.74
6.74
0.98
1.41
0.82
0.72
P for trend
< 0.001
0.580
0.695
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
< 0.001
*For participants with complete data on all study variables including health and work environment (11,548 women and 12,025 men).
**Values reported in the text are slightly different because they are based on analyses which did not require complete data.
mates of this association the most (–76.6 % among the women
and –65.3 % among the men), explaining virtually all of the reduction of the association shown in Table 5.
for men. We also found a dose-response relationship between
work-related sleep disturbances and medically-certified sickness absence in women and men. This association was robust
to adjustments for demographic and regional characteristics,
supervisory position, and measures of work environment, and
was strengthened with time in women. Increasing trends in depressive symptoms explained most of the association between
work-related sleep disturbances and sickness absence.
To the best of our knowledge, no prior population-based studies of secular trends in work-related sleep disturbances are avail-
DISCUSSION
This study of the Swedish working population shows that
the age-adjusted prevalence of self-reported work-related sleep
disturbances, experienced at least once a week, increased from
12% in 1993 to 22% in 1999 for women, and from 12% to 19%
SLEEP, Vol. 31, No. 8, 2008
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Sleep Disturbances and Sickness Absence 1993-1999—Westerlund et al
Table 3—Cross-Sectional Association Between Self-Reported Work-Related Sleep Disturbances and Having had at Least One Sick-Leave
Spell > 14 Days; Results for Women
Have you during the last 3 months
n
n (%) with at least one
OR (95 % CI) for having at least one
had difficulties sleeping because
sick-leave spell of >14
sick-leave spell of >14 consecutive days
thoughts of work have kept you awake?
consecutive days
Adjusted for age Adjusted for age Adjusted for age
+ supervisory
+ supervisory
position
position
+ region
SWES 1993
Not at all/Seldom last 3 months
3506
583 (16.6)
1
1
1
A couple of days a month
1014
158 (15.6)
0.89 (0.74–1.08) 0.92 (0.76–1.12) 0.93 (0.76–1.12)
One day a week
352
62 (17.6)
0.99 (0.74–1.32) 1.03 (0.77–1.37) 1.04 (0.77–1.39)
A couple of days a week
232
45 (19.4)
1.10 (0.78–1.54) 1.15 (0.82–1.62) 1.15 (0.82–1.62)
Every day
58
24 (41.4)
3.15 (1.84–5.40) 3.20 (1.87–5.48) 3.22 (1.88–5.50)
SWES 1995
Not at all/Seldom last 3 months
2894
457 (15.8)
1
1
1
A couple of days a month
976
163 (16.7)
1.04 (0.86–1.27) 1.09 (0.89–1.32) 1.09 (0.90–1.33)
One day a week
393
80 (20.4)
1.31 (1.00–1.70) 1.36 (1.04–1.79) 1.38 (1.05–1.80)
A couple of days a week
321
69 (21.5)
1.31 (0.98–1.75) 1.39 (1.04–1.86) 1.42 (1.06–1.89)
Every day
51
23 (45.1)
3.81 (2.16–6.71) 3.88 (2.20–6.85) 3.98 (2.25–7.03)
SWES 1999
Not at all/Seldom last 3 months
2376
353 (14.9)
1
1
1
A couple of days a month
1020
154 (15.1)
0.97 (0.79–1.19) 0.99 (0.80–1.22) 0.99 (0.80–1.22)
One day a week
476
104 (21.8)
1.54 (1.20–1.97) 1.59 (1.24–2.04) 1.59 (1.24–2.04)
A couple of days a week
431
108 (25.1)
1.75 (1.37–2.25) 1.82 (1.42–2.34) 1.83 (1.42–2.35)
Every day
119
53 (44.5)
4.03 (2.74–5.92) 4.17 (2.83–6.13) 4.13 (2.81–6.08)
Odds Ratios (OR) and 95% Confidence Intervals (CI).
able for comparison, but raw data on the increase in self-reported
sleep disturbances in Sweden have been reported previously.21
Our findings are consistent with the international trends of increased mental health complaints.27,35 Increase in reported workrelated sleep disturbances could reflect a number of things: increasing objective sleep disturbances; an increasing tendency to
report sleep disturbances; or an increased tendency to attribute
sleep disturbances to problems in the work situation (which in
turn could reflect either deteriorating work environment, a stronger objective association between work and sleep, or a cultural
tendency to blame health problems on work). An increased public awareness of both sleep disturbances and psychosocial work
environment as reflected in the media could have contributed to
both increased reporting and attribution to work.
In the years this study covers, the prevalence of long-term
sickness absence increased in Sweden, especially among women.36 However, this was not reflected in our data, since only
currently working individuals were included in SWES (in effect
excluding most cases of very long absences and all full-time
disability pensioners). Plausible explanations for the increase
in sickness absence in the population have been extensively
discussed without reaching clear conclusions. It can be hypothesized that the substantial increase in work-related sleep
disturbances is one explanation.14 Other surveys in Sweden
have for the same years shown a trend of increasing demands
among both male and female employees in female-dominated
occupations.37 A corresponding increase in male-dominated or
gender-integrated occupations was not found. In the present
study, there were indeed significant changes in psychosocial
work environment for both women and men. However, adding
demands and other work environment variables to the analySLEEP, Vol. 31, No. 8, 2008
ses of our data affected the associations between work-related
sleep disturbances and sickness absence only marginally, which
indicates that work-related sleep disturbances may be independently associated with sickness absence.
Other stressors, such as job insecurity and immediate threat
of job loss, have been shown to be associated with fatigue and
sleep disturbances,38-40 as well as with sickness absence,41-43 and
could thus potentially explain an association between work-related sleep disturbances and sickness absence. However, since
we excluded all subjects who had received unemployment benefit during the survey years, this is unlikely to explain the associations found in this paper.
As our findings are based on repeated cross-sectional measurements, we do not know if work-related sleep disturbances
caused sickness absence, or vice versa, or whether the association could be attributable to confounding. Some studies indicate
that sleep disturbances lead to sickness absence,11,14 but it is also
conceivable that sleep disturbances are caused by worries over
work that sick-listed people have, or by other consequences of
sickness absence (which could in turn impede return to work).
The scientific knowledge base of any type of consequence, positive or negative, of sickness absence is very limited.36 We found
only one such study on consequences on sleep; a retrospective study of 862 persons who were or had been on long-term
sickness absence.12 That study suggested that sickness absence
might have consequences for sleep: about two-thirds reported
negative effects and one in ten reported positive effects.
The fact that the increasing secular trend in work-related
sleep disturbances was not paralleled by a similar trend in sickness absence in our data suggests that sleep disturbances are not
a dominant determinant of the incidence of sickness absenc1173
Sleep Disturbances and Sickness Absence 1993-1999—Westerlund et al
Table 4—Cross-Sectional Association Between Self-Reported Work-Related Sleep Disturbances and Having had at Least One Sick-Leave
Spell > 14 Days; Results for Men
Have you during the last 3 months
n
n (%) with at least one
OR (95 % CI) for having at least one
had difficulties sleeping because sick-leave spell of >14
sick-leave spell of >14 consecutive days
thoughts of work have kept you awake?
consecutive days
Adjusted for age Adjusted for age Adjusted for age
+ supervisory
+ supervisory
position
position
+ region
SWES 1993
Not at all/Seldom last 3 months
3421
358 (10.5)
1
1
1
A couple of days a month
1096
90 ( 8.2)
0.74 (0.58–0.94) 0.81 (0.64–1.04) 0.81 (0.64–1.04)
One day a week
370
44 (11.9)
1.08 (0.77–1.51) 1.20 (0.85–1.68) 1.20 (0.86–1.68)
A couple of days a week
218
36 (16.5)
1.56 (1.07–2.28) 1.65 (1.13–2.42) 1.66 (1.13–2.42)
Every day
68
19 (27.9)
3.00 (1.74–5.18) 3.26 (1.87–5.66) 3.26 (1.88–5.68)
SWES 1995
Not at all/Seldom last 3 months
3043
281 ( 9.2)
1
1
1
A couple of days a month
980
85 ( 8.7)
0.87 (0.68–1.13) 0.93 (0.74–1.25) 0.97 (0.75–1.26)
One day a week
384
42 (10.9)
1.10 (0.78–1.56) 1.23 (0.87–1.75) 1.23 (0.87–1.75)
A couple of days a week
298
48 (16.1)
1.63 (1.16–2.28) 1.89 (1.34–2.66) 1.89 (1.34–2.67)
Every day
59
16 (27.1)
2.92 (1.60–5.31) 3.29 (1.79–6.04) 3.30 (1.80–6.06)
SWES 1999
Not at all/Seldom last 3 months
2529
229 ( 9.1)
1
1
1
A couple of days a month
911
80 ( 8.8)
0.91 (0.69–1.19) 0.94 (0.72–1.23) 0.94 (0.71–1.23)
One day a week
424
60 (14.2)
1.53 (1.12–2.09) 1.62 (1.19–2.22) 1.62 (1.19–2.21)
A couple of days a week
328
45 (13.7)
1.42 (1.01–2.02) 1.55 (1.09–2.20) 1.55 (1.09–2.20)
Every day
76
25 (32.9)
4.14 (2.49–6.88) 4.27 (2.56–7.12) 4.26 (2.56–7.10)
Odds Ratios (OR) and 95% Confidence Intervals (CI).
Table 5—Effects of Adjustment for Work Environment and Health Indicators on the Associations Between Work-Related Sleep Disturbances
and Sickness Absence 1993-1999
Have you in the last 3 months
n
Adjustments
had difficulties sleeping because
Model A: age, supervisory
A + work
thoughts of work have kept you awake?
position, region, and
environment
survey year
WOMEN Not at all/Seldom last 3 months
7112
1
1
A couple of days a month
2489
0.98 (0.86–1.11)
0.98 (0.86–1.12)
One day a week
988
1.35 (1.14–1.60)
1.29 (1.08–1.55)
A couple of days a week
791
1.44 (1.20–1.73)
1.32 (1.08–1.60)
Every day
168
3.56 (2.59–4.90)
3.09 (2.21–4.31)
Change in Odds Ratio**
± 0%
– 18.3%
MEN
Not at all/Seldom last 3 months
7621
1
1
A couple of days a month
2539
0.82 (0.69–0.96)
0.88 (0.74–1.04)
One day a week
1001
1.28 (1.03–1.58)
1.35 (1.08–1.68)
A couple of days a week
707
1.63 (1.30–2.04)
1.75 (1.38–2.23)
Every day
157
3.88 (2.71–5.55)
4.18 (2.86–6.12)
Change in Odds Ratio**
± 0%
+ 10.4%
A + hospital
admission and selfreported symptoms*
1
0.81 (0.70–0.94)
0.87 (0.72–1.07)
0.80 (0.65–1.00)
1.69 (1.16–2.46)
– 73.0%
1
0.74 (0.62–0.89)
0.94 (0.74–1.19)
0.97 (0.74–1.26)
1.73 (1.13–2.66)
– 74.7%
*Depressive symptoms, physical exhaustion, psychosomatic symptoms, and musculoskeletal symptoms.
**Compared with Model A odds ratios for the response alternative every day.
es longer than 14 days, that other determinants have become
less important, or that there is a time lag between the trends.
However, in a previous Swedish study work-related sleep disturbances prospectively predicted sickness absences longer
than 90 days,14 an outcome which was poorly represented in
our study. The strengthening of the association between sleep
SLEEP, Vol. 31, No. 8, 2008
disturbances and sickness absence over time in women may
mean that work-related sleep disturbances and sickness absence
increasingly co-occurred in this group, either because the significance of such sleep disturbances as determinants of sickness
absence was increasing over time or because sickness absence
or other factors increasingly caused sleep disturbances.
1174
Sleep Disturbances and Sickness Absence 1993-1999—Westerlund et al
Table 6—Effects of Adjustment for Different Health Measures on the Associations Between Work-Related Sleep Disturbances and Sickness
Absence 1993-1999
Have you in the last 3 months
Adjustments
had difficulties sleeping because
A* + hospital
A* + depressive
A* + physical A* + psychosomatic A* + musculoskeletal
thoughts of work have kept
admission
symptoms
exhaustion
symptoms
symptoms
you awake?
WOMEN Not at all/Seldom last 3 months 1
1
1
1
1
A couple of days a month
0.99 (0.87–1.14) 0.83 (0.73–0.95) 0.88 (0.77–1.01) 0.88 (0.78–101)
0.88 (0.77–1.00)
One day a week
1.32 (1.10–1.59) 0.95 (0.80–1.14) 1.06 (0.89–1.26) 1.08 (0.91–1.29)
1.08 (0.91–1.30)
A couple of days a week
1.46 (1.20–1.78) 0.84 (0.69–1.04) 1.02 (0.84–1.24) 1.05 (0.86–1.27)
1.04 (0.86–1.26)
Every day
3.77 (2.69–5.28) 1.60 (1.14–2.26) 2.22 (1.60–3.10) 2.28 (1.64–3.18)
2.36 (1.69–3.31)
Change in Odds Ratio**
+ 8.2%
– 76.6%
– 52.3%
– 50.0%
– 46.9%
MEN
Not at all/Seldom last 3 months 1
1
1
1
1
A couple of days a month
0.81 (0.68–0.96) 0.72 (0.61–0.85) 0.78 (0.66–0.92) 0.77 (0.65–0.91)
0.80 (0.68–0.95)
One day a week
1.31 (1.05–1.63) 0.95 (0.76–1.17) 1.06 (0.86–1.32) 1.06 (0.85–1.31)
1.07 (0.86–1.33)
A couple of days a week
1.63 (1.28–2.07) 1.02 (0.80–1.30) 1.22 (0.96–1.54) 1.26 (1.00–1.60)
1.19 (0.94–1.51)
Every day
3.85 (2.62–5.65) 2.00 (1.36–2.95) 2.38 (1.64–3.46) 2.56 (1.76–3.73)
2.45 (1.67–3.60
Change in Odds Ratio**
– 1.0%
– 65.3%
– 52.1%
– 45.8%
– 49.7%
*Odd ratios for Model A are presented in Table 5.
**Compared with Model A odds ratios for the response alternative every day.
From other research, we know that disturbed sleep and short
sleep are related to morbidity,2-9 particularly depression,32,44-47
and to mortality,48 and there is a correlation between work
stress and sleep.49,50 A plausible hypothesis would thus be that
sleep disturbances induce health problems that are reflected in
increased sick-leave rates. The observed attenuation of the relationship between work-related sleep disturbances and sickness absence with adjustment for depressive symptoms (rather
than other health measures) indicates that the association may
be mediated by depressive symptoms. It is also possible that the
observed sleep disturbances, despite being attributed to workrelated causes, are in fact symptoms of depression, which may
be the underlying cause of both sleep disturbances and sickness absence, or that sleep disturbances are part of a larger
syndrome that includes depressive symptoms.45 From earlier
research we know that sleep disturbances tend to precede the
onset of depression,47,51,52 suggesting either a causal relationship
from sleep disturbance to depression or that sleep disturbances
are early symptoms of depression. The increasing trends found
for work-related sleeping problems and depressive symptoms
are largely parallel to observed increases in antidepressant
treatment53 and long sick-leaves for mental disorders54 and
depression,55 suggesting that the depressive symptoms measured in our study may be associated also with clinical levels of
depression. Further research is needed to clarify the mechanisms
linking sleep disturbances, health and environmental stress.
absences typically caused by minor health problems such as
colds.56 Records of sick leaves longer than 14 days were certified by a physician and did not include absence for care of newborn or sick children, which is treated separately from sickness
absence in the public records.
The exact number of people varied slightly between the
years, but the sampling procedure remained the same. Since
SWES is intended to be representative of the Swedish working
population at the time of the survey, the demographic characteristics change over time as a reflection of the demographic
changes in the working population. Thus, our study indicates an
increased prevalence of work-related sleep disturbances in the
working population and similar trends were found for depressive symptoms and other self-reported health problems.
A potential source of bias, however, is the fact that attrition increased over time in SWES (as in most other surveys in
Sweden).57 Persons with health problems tend to be more likely
than healthy people to become non-respondents,58,59 potentially
contributing to an underestimation of the rise in work-related
sleep disturbances. In the present data, men, young workers and
persons with low socioeconomic status were also overrepresented in the drop-out group.60 However, the multivariate analyses
took into account the effect of some of these characteristics (i.e.,
the separate models for men and women were adjusted for measures of work environment) and this did not substantially change
age-standardized estimates. This is evidence against the possibility that bias due to accelerated sample attrition would explain the
observed increase in work-related sleep disturbances.
Finally, the two items used to measure depressive symptoms
have not been validated against a diagnosis of major depression. Thus, it remains unclear to what extent clinical depression,
nonclinical depressive symptoms, and other characteristics of
the respondents, affected the association between self-reported
sleep disturbances attributed to work-related causes and medically-certified sickness absence.
Methodological Considerations
The main strengths of the present study are that it is based on
large, random samples of the national working population from
several years, and that the sickness absence data are registry
based and of good quality. Furthermore, we include only longer sick-leave spells (>14 days) reflecting more long-standing
illnesses15 and unavoidable work disability, rather than short
SLEEP, Vol. 31, No. 8, 2008
1175
Sleep Disturbances and Sickness Absence 1993-1999—Westerlund et al
Conclusion
13. Ohayon MM, Lemoine P, Arnaud-Briant V, Dreyfus M. Prevalence and consequences of sleep disorders in a shift worker population. J Psychosom Res 2002;53:577-83.
14. Akerstedt T, Kecklund G, Alfredsson L, Selen J. Predicting
long-term sickness absence from sleep and fatigue. J Sleep Res
2007;16:341-5.
15. Marmot M, Feeney A, Shipley M, North F, Syme SL. Sickness
absence as a measure of health status and functioning: from
the UK Whitehall II study. J Epidemiol Community Health
1995;49:124-30.
16. Ota A, Masue T, Yasuda N, Tsutsumi A, Mino Y, Ohara H. Association between psychosocial job characteristics and insomnia: an
investigation using two relevant job stress models--the demandcontrol-support (DCS) model and the effort-reward imbalance
(ERI) model. Sleep Med 2005;6:353-8.
17. Linton SJ. Does work stress predict insomnia? A prospective
study. Br J Health Psychol 2004;9:127-36.
18. Dahlgren A, Kecklund G, Akerstedt T. Different levels of workrelated stress and the effects on sleep, fatigue and cortisol. Scand
J Work Environ Health 2005;31:277-85.
19. Greenberg J. Losing sleep over organizational injustice: attenuating insomniac reactions to underpayment inequity with supervisory
training in interactional justice. J Appl Psychol 2006;91:58-69.
20. Ancoli-Israel S, Roth T. Characteristics of insomnia in the United
States: results of the 1991 National Sleep Foundation Survey. I.
Sleep 1999;22 Suppl 2:S347-53.
21. Stefansson CG. Chapter 5.5: major public health problems - mental ill-health. Scand J Public Health Suppl 2006;67:87-103.
22. Lehto A-M, Sutela H. Results from work life surveys 1977-2003.
Helsinki: Statistics Finland, 2004.
23. Persson G, Danielsson M, Rosen M, et al. Health in Sweden: the
National Public Health Report 2005. Scand J Public Health Suppl
2006;67:3-10.
24. Kronholm E, Partonen T, Laatikainen T, et al. Trends in self-reported sleep duration and insomnia-related symptoms in Finland
from 1972 to 2005: a comparative review and re-analysis of Finnish population samples. J Sleep Res 2008;17:54-62.
25. Horne J. Is there a sleep debt? Sleep 2004;27:1047-9.
26. Shiels C, Gabbay MB, Ford FM. Patient factors associated with
duration of certified sickness absence and transition to long-term
incapacity. Br J Gen Pract 2004;54:86-91.
27. Järvisalo J, Anderson B, Boedeker W, Houtman I. Mental disorders as a major challenge in prevention of work disability. Helsinki: Kela, 2005.
28. Stansfeld S, Feeney A, Head J, Canner R, North F, Marmot M.
Sickness absence for psychiatric illness: the Whitehall II Study.
Soc Sci Med 1995;40:189-97.
29. Vaez M, Rylander G, Nygren A, Asberg M, Alexanderson K.
Sickness absence and disability pension in a cohort of employees
initially on long-term sick leave due to psychiatric disorders in
Sweden. Soc Psychiatry Psychiatr Epidemiol 2007;42:381-8.
30. Hensing G, Wahlström R. Sickness absence and psychiatric disorders. In: Alexanderson K, Norlund A, (Eds). Sickness absence
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on Technology Assessment in Health Care. Scand J Public Health
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31. Lindholm C, Fredlund P, Backhans M. Hälsotillstånd och sjukskrivningsutveckling. [Health status and development of sickness
absence. In Swedish.]. In: Marklund S, Bjurvald M, Hogstedt C,
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32. Nakata A, Haratani T, Takahashi M, et al. Association of sickness
Our findings from population-based surveys between 1993
and 1999 indicate that self-reported sleep disturbances attributed to work-related causes were on the rise in Sweden and
were associated with medically-certified sickness absence. A
substantial part of the association seems to be related to depressive symptoms, but further research is needed to determine the
exact nature of this association.
Acknowledgments
We wish to thank all the participants in the Swedish Work
Environment Surveys, Statistics Sweden, Centre for Epidemiology at the Swedish National Board of Health and Welfare for
their respective contributions. We also thank Dr. Gabriel Oxenstierna for his original idea to merge the databases into the one
used in this project. The database used was financed by a research grant from the Swedish Council for Work Life Research
(Vinnova, Grant # P23216-1A). The study was funded by the
Swedish Council for Work Life Research (RALF) and the
Swedish Council for Working Life and Social Research (FAS)
(FAS, grant #2004-2021). MK is supported by the Academy of
Finland (grants number 117604,124322, and 124271).
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Appendix: Items used for measurement of health-related
symptoms
All items are rated on a 5-point Likert scale, coded 4–0: Every day; A couple of days a week (1 day of 2); One day a week
(1 day of 5); A couple of days a month (1 day of 10); Not at all/
Seldom last 3 months.
Depressive Symptoms (After Exclusion of Items Referring to
Sleep):
1. During the last 3 months have you been tired and listless?
2. Does it happen that you feel ill at ease going to your job?
Physical Exhaustion:
1. Does it happen that you are physically exhausted when
you get home from work?
Psychosomatic Symptoms:
During the last 3 months have you...
1. ...had heartburn, acid burping, a burn in the pit of your
stomach, or upset stomach?
2. ...had headaches?
Musculoskeletal Symptoms:
After work, do you experience pain in any of the following
places...
1. ...upper parts of your back or neck?
2. ...lower parts of your back?
3. ...shoulders or arms?
4. ...wrists or hands?
5. ...hips, legs, knees, or feet?
1177
Sleep Disturbances and Sickness Absence 1993-1999—Westerlund et al