European Journal of Public Health, 1–6
? The Author 2013. Published by Oxford University Press on behalf of the European Public Health Association. All rights reserved.
Sleep problems, exercise and obesity and risk of chronic
musculoskeletal pain: The Norwegian HUNT study
Paul Jarle Mork1, Kirsti Lund Vik1,2, Børge Moe1, Ragnhild Lier1,2, Ellen Marie Bardal1,
Tom Ivar Lund Nilsen1
1 Department of Human Movement Science, Norwegian University of Science and Technology, Trondheim, Norway
2 Liaison Committee between the Central Norway Regional Health Authority (RHA), Stjørdal, Norway, and the
Norwegian University of Science and Technology (NTNU), Trondheim, Norway
Correspondence: Paul Jarle Mork, Department of Human Movement Science, Norwegian University of Science and
Technology, N-7491 Trondheim, Norway, Tel: +47 73 59 04 47, Fax: + 47 73 59 17 70, e-mail: firstname.lastname@example.org
Background: The objective was to investigate the association between self-reported sleep problems and risk of
chronic pain in the low back and neck/shoulders, and whether physical exercise and body mass index (BMI) alter
this association. Methods: The study comprised data on 26896 women and men in the Nord-Trøndelag Health
Study (Norway) without chronic pain or physical impairment at baseline in 1984–86. Occurrence of chronic pain was
assessed at follow-up in 1995–97. A generalized linear model was used to calculate adjusted risk ratios. Results:
Sleep problems were dose-dependently associated with risk of pain in the low back and neck/shoulders in both
women and men (P<0.001 both genders). Women and men who reported sleep problems ‘sometimes’ and ‘often/
always’ had a higher risk of chronic pain of 23–32% and 51–66%, respectively, than those who reported sleep
problems ‘never’. Combined analyses showed that persons with sleep problems ‘sometimes’ and who exercised ?1
hour per week had lower risk of chronic pain in the low back (P<0.04) and neck/shoulders (P<0.001) than inactive
persons with a similar level of sleep problems (P<0.04). Likewise, persons with BMI <25kg/cm2and sleep problems
‘sometimes’ had lower risk of chronic pain in the low back (P<0.001) and neck/shoulders (P<0.001) than persons
with BMI ?25kg/cm2and a similar level of sleep problems. Conclusion: Sleep problems are associated with an
increased risk of chronic pain in the low back and neck/shoulders. Regular exercise and maintenance of normal
body weight may reduce the adverse effect of mild sleep problems on risk of chronic pain.
pain are among the most significant contributors to years lived
with disability1and disability-adjusted life years.2The negative
impact of chronic musculoskeletal pain, both on the individual
and the society, underscores the importance of identifying primary
preventive measures that are easily accessible for most people.
Sleep, physical exercise and body weight are modifiable and
interrelated risk factors that are important for musculoskeletal
health. Sleep problems have been associated with an increased risk
of chronic pain in the low back and neck/shoulders,3widespread
chronic musculoskeletal pain4–6and exacerbation of musculoskeletal
symptoms in pain-afflicted individuals.7Conversely, regular exercise
and normal body weight have been associated with a reduced risk of
both localized8–10and widespread chronic pain.11,12Thus, sleep
problems and maintenance of a healthy lifestyle appear to have con-
trasting effects on the risk of chronic musculoskeletal pain.
The objective of this study was to prospectively investigate the
association between sleep problems and risk of chronic pain in the
low back and neck/shoulders, and whether physical exercise and
body mass index (BMI) alter this association. Using data from a
large unselected population of women and men without chronic
pain at baseline, we hypothesized that a positive association exists
between sleep problems and a risk of chronic pain in the low back
and neck/shoulders, and that physical exercise and a normal BMI
compensate for the adverse effect of sleep problems on risk of
chronic pain in the low back and neck/shoulders.
recent global health survey showed that low back pain and neck
In Nord-Trøndelag County, Norway, all inhabitants ?20 years of age
were invited to participate in two large health surveys (the
Nord-Trøndelag Health Study [HUNT]), first in 1984–86 (HUNT1)
and then in 1995–97 (HUNT2). Among 87285 eligible persons, 77216
(89%) accepted the invitation to HUNT1. The participants filled in
questionnaires and underwent a clinical examination. For HUNT2,
94187 persons were invited to participate, of which 66215 (70%)
accepted the invitation. The procedures were similar as those
described for HUNT1, although the questionnaires and the clinical
examination were more comprehensive. Detailed information about
the HUNT Study can be found at http://www.ntnu.edu/hunt.
For the purpose of this study, we included all 24357 women and
21568 men who had participated in both surveys (figure 1). Of
these, we excluded all participants with missing information on
musculoskeletal pain, BMI and sleep problems. Moreover, we
excluded all participants with physical impairment, chronic muscu-
loskeletal pain or who used sedative and/or sleeping medicine on a
daily/weekly basis at baseline. Thus, the prospective analyses of
chronic pain in neck/shoulders and low back were based on 13501
women and 13395 men. All participants gave a written informed
consent upon participation. The study was approved by the Regional
Committee for Ethics in Medical Research and carried out according
to the Declaration of Helsinki.
Sleep problems at baseline were assessed by the question ‘During the
last month, have you had any problems falling asleep or sleep
problems?’ Response options were ‘never’, ‘sometimes, ‘often’ and
‘almost every night’. The two latter categories were collapsed into
‘often/always’ in the statistical analyses.
At baseline, the participants were asked to complete a questionnaire
that included questions on frequency, duration and intensity of
The European Journal of Public Health Advance Access published November 28, 2013
leisure time physical exercise per week (i.e. walking, skiing,
swimming or other sports). The frequency question allowed five
response options (0, <1, 1, 2–3 or ?4 times per week).
Participants exercising at least once a week were also asked about
the average duration per session (<15, 15–30, 31–60 or >60 minutes)
and the average intensity of the activity (light, moderate or
Based on information on frequency and duration, we calculated
the average number of exercise hours per week. In the calculation,
the response option 2–3 times per week was counted as 2.5 times,
and ?4 times per week was counted as 5 times. For duration, the
response option <15 minutes was counted as 10 minutes, 15–30
minutes was counted as 25 minutes, 31–60 minutes was counted
as 45 minutes, and >60 minutes was counted as 75 minutes. In
the analyses of the combined effect of sleep problems and physical
exercise, participants who accumulated ?1 hour exercise per week
were classified as physically active, whereas those who reported no
activity or <1 exercise session per week were classified as inactive.
Body mass index
Standardized measurements of body height (to the nearest
centimeter) and body mass (to the nearest half kilogram) obtained
at the baseline clinical examination were used to calculate BMI as
body mass divided by the squared value of height (kg/m2).
Participantswere then classified
according to the cut-points suggested by the World Health
i.e. underweight (BMI <18.5kg/m2), normal
weight (BMI 18.5–24.9kg/m2), overweight (BMI 25.0–29.9kg/m2)
and obese (BMI ?30.0kg/m2). A dichotomous BMI variable
(?25kg/m2) was used in the analyses of the combined effect of
sleep problems and BMI.
intofour BMI categories
Chronic musculoskeletal pain
The questions about musculoskeletal symptoms were adopted from
the Standardized Nordic Questionnaire.14For HUNT2, the partici-
pants were asked ‘During the last year, have you had pain and/or
stiffness in your muscles and limbs that lasted for at least three
consecutive months?’, with response options ‘yes’ and ‘no’. If the
participants answered yes, they were asked to indicate the affected
body area(s). In the statistical analyses, chronic pain in neck,
shoulders and upper back was combined to indicate chronic pain
in neck/shoulders, whereas chronic pain in the low back was
A generalized linear model of the binomial family (log link) was used
to estimate the risk ratios (RRs) for chronic pain in the low back and
neck/shoulders. Women and men who reported ‘sometimes’ or
‘often/always’ sleep problems during the past month were
compared with the reference group of women and men who
‘never’ had experience sleep problems in the past month. Precision
of the estimated RRs was assessed by 95% confidence intervals (CIs),
and trend tests across categories of sleep problems were calculated by
treating the categories as ordinal variables in the regression model.
Our basic model was adjusted for age in 10-year categories (20–29,
30–39,...,60–69 or ?70 years). In multivariable models, we
adjusted for BMI (underweight, normal weight, overweight or
obesity), frequency of physical exercise (inactive, 1, 2–3 or ?4
times per week, or unknown), psychological well-being (depressed,
somewhat happy, happy or unknown), smoking status (never,
former, current or unknown) and occupation (manual, non-
manual, farmer/fisher, non-worker or unknown). Further, we
examined the combined effect of physical exercise (i.e. inactive vs.
exercise ?1 hour/week) and different levels of sleep problems using
physically inactive participants without sleep problems as the
reference group. Similar analysis was performed for the combined
effect of BMI (?25.0kg/m2) and different levels of sleep problems
using participants without sleep problems and a BMI ?25.0kg/m2as
the reference group. To assess potential statistical interaction, we
conducted likelihood ratio tests, including the product terms of
physical exercise and sleep problems, and of BMI and sleep
problems, in the regression model. The effect of physical exercise
and BMI within each category of sleep problems was estimated in
the subsequent stratified analyses. All statistical tests were two-sided,
and all statistical analyses were performed using Stata for Windows,
version 12.1 (StataCorp LP, College Station, Texas).
Table 1 presents the characteristics of the study population
according to frequency of sleep problems at baseline. More
‘sometimes’ (30 vs. 23%) and ‘often/always’ (3.2 vs. 2.2%) during
the past month. At follow-up, 2379 (18%) women and 1824 (14%)
men reported chronic pain in the low back, whereas 3573 (26%)
women and 2892 (22%) men reported chronic pain in the neck/
Figure 1 Selection of study participants
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European Journal of Public Health
Table 2 shows that frequency of sleep problems was dose-depend-
ently associated with the risk of chronic pain in the low back and
neck/shoulders (P<0.001 in both genders and for both pain
locations). Compared with those without sleep problems, women
and men who experienced sleep problems ‘sometimes’ had
adjusted RRs for low back pain of 1.32 (95% CI: 1.22–1.43) and
1.30 (95% CI: 1.18–1.43), respectively. The RR increased further
among women and men who experienced sleep problems ‘often/
always’ (RRs=1.66, 95% CI: 1.41–1.95 in women, and RRs=1.51,
95% CI: 1.20–1.91 in men). The association between sleep problems
and the risk of chronic pain in neck neck/shoulders followed a
pattern similar to that for low back pain: Women and men who
experienced sleep problems ‘sometimes’ had RRs of 1.31 (95% CI:
1.24–1.40) and 1.23 (95% CI: 1.15–1.33), respectively, whereas sleep
problems ‘often/always’ were associated with RRs of 1.53 (95% CI:
1.35–1.74) in women and 1.58 (95% CI 1.35–1.86) in men.
Table 3 shows the combined effect of sleep problems and physical
exercise on risk of chronic pain in the low back and neck/shoulders.
There was no evidence of statistical interaction between sleep
problems and physical exercise (P-values from likelihood ratio
tests were 0.63 for low back pain and 0.98 for neck/shoulder
pain). However, in stratified analyses, persons with sleep problems
‘sometimes’ had an RR of 1.32 (95% CI: 1.20–1.44) for low back
pain if they were inactive, and an RR of 1.16 (95% CI 1.05-1.29) if
they exercised ?1 hour per week (P-value for homogeneity of RRs,
0.04). The corresponding RRs for neck/shoulder pain were 1.09
(95% CI: 1.00–1.18) and 1.27 (95% CI: 1.19–1.36), respectively
The combined effect of sleep problems and BMI on risk of chronic
pain in the low back and neck/shoulders is presented in table 4.
There was no evidence of statistical interaction (P-values from
likelihood ratio tests were 0.45 for low back pain and 0.82 for
neck/shoulder pain), but stratified analyses showed that persons
with sleep problems ‘sometimes’ and a BMI ?25kg/m2had an RR
of 1.31 (95% CI: 1.20–1.44) for low back pain, whereas the RR was
1.17 (95% CI: 1.08–1.28) among persons with BMI <25kg/m2and
the same level of sleep problems (P-value for homogeneity of RRs,
<0.001). The corresponding RRs for neck/shoulder pain were 1.25
(95% CI: 1.16–1.34) and 1.13 (95% CI: 1.06–1.20), respectively
This study shows a positive and dose-dependent association between
frequency of sleep problems and risk of chronic pain in the low back
and neck/shoulders. Compared with those who ‘never’ experienced
sleep problems, women and men who ‘sometimes’ experienced sleep
problems had a 23–32% increased risk of chronic pain, whereas
women and men who ‘often/always’ had sleep problems had a
51–66% increased risk. Women and men with sleep problems
‘sometimes’ and who exercised ?1 hour per week had lower risk
of chronic pain in the low back and neck/shoulders than inactive
women and men with the same level of sleep problems. A similar
association was observed between sleep problems and BMI, i.e.
women and men having sleep problems ‘sometimes’ and BMI
<25kg/m2had lower risk of chronic pain in the low back and
neck/shoulders than women and men with BMI >25kg/m2and
same level of sleep problems.
Our finding of an increased risk of chronic musculoskeletal pain
among persons with sleep problems is in agreement with findings
in other prospective studies.3,4,6A cohort study including 4463
vocationally active and healthy middle-aged women and men
(aged 45–64 years old) showed that mild to severe sleep problems
were associated with odds of 72% in men and 91% in women for
chronic pain in the low back and neck/shoulders at 1-year follow-
up.3Sleep problems have also been associated with an increased risk
of low back pain and hospitalization because of back disorders in
industry workers.15,16Moreover, some studies have shown that sleep
problems are associated with an increased risk of widespread chronic
pain.4,6Morphy et al.6found that insomnia was associated with a
45% increased risk of widespread pain at 1-year follow-up in
a general population of 2363 women and men (age >18 years). A
recent prospective study of 12350 women in HUNT1 showed that
sleep problems constitute a major risk factor for fibromyalgia.4In
the latter study, the definition of sleep problems was identical to that
used in the current study, and showed a three- to five-fold increased
risk of fibromyalgia among women who reported to have sleep
problems ‘often/always’. Thus, the findings in the current study,
together with other prospective data, provide convincing evidence
that sleep problems represent an independent risk factor for chronic
It is not clear why sleep problems increase the risk of chronic
musculoskeletal pain. A possible mechanism may be that poor
sleep induces a state of low-level systemic inflammation that con-
tributes to sensitize the nociceptive system. Experimental studies
have shown that sleep deprivation induces elevated plasma levels
of pro-inflammatory cytokines such as interleukin-6 (IL-6), IL-8
and tumour necrosis factor-?.17–19Although the role of pro- and
anti-inflammatory cytokines in conditions with chronic musculo-
skeletal pain is unclear,20–22it has been shown that elevated levels
of IL-6 after sleep restriction are strongly associated with increased
pain ratings in healthy individuals.17Moreover, some evidence
indicates that pro-inflammatory cytokines are involved in the pro-
gression of chronic pain,23–25and that the serum level of these
cytokines predicts pain intensity in chronic pain patients.26
Importantly, the current study indicates that maintenance of
normal body weight or accumulation of ?1 hour of physical
exercise per week can reduce the adverse effect of mild sleep
problems on musculoskeletal health. Similar to sleep problems,
physical inactivity and obesity are associated with low-graded
Table 1 Baseline characteristics of the study population categorized by severity of sleep problems
No. of persons (%)
Age (years), mean (SD)
BMI (kg/m2), mean (SD)
Overweight or obese,ano. (%)
Physically inactive,bno. (%)
Depressed, no. (%)
Current smoker, no. (%)
Manual worker, no. (%)
BMI: body mass index.
b<1 exercise session per week.
The Norwegian HUNT study
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Table 2 RR for chronic pain in the low back and neck/shoulders at 11-year follow-up according to frequency of sleep problems at baseline
Pain location, gender and frequency
of sleep problems
No. of personsNo. of cases Age-adjustedaRR MultiadjustedbRR (95% CI)P for trend
Low back, women
Low back, men
1.51 (1.20–1.91) 62<0.001
aAdjusted for age (20–29, 30–39,...or ?70 years).
bAdjusted for age (20–29, 30–39,...or ?70 years), physical exercise (none, <1, 1, 2–3 or ?4 sessions per week, or unknown), BMI (under-
weight, normal weight, overweight or obesity), psychological well-being (depressed, somewhat happy, happy or unknown), smoking status
(never, former, current or unknown) and occupation (manual, non-manual, farmer/fisher, non-worker or unknown).
Table 3 RR for chronic pain in the low back and neck/shoulders at 11-year follow-up according to the combined effect of frequency of sleep
problems and leisure time physical exercise at baseline
Pain location and frequency
of sleep problems
RR (95% CI)
RR (95% CI)
a<1 physical exercise session per week.
bOne or more hours of physical exercise per week.
cP-value comparing physically active and inactive persons within each category of sleep problems.
dAdjusted for age (20–29, 30–39,...or ?70 years), BMI (underweight, normal weight, overweight or obesity), psychological well-being
(depressed, somewhat happy, happy or unknown), smoking status (never, former, current or unknown) and occupation (manual, non-
manual, farmer/fisher, non-worker or unknown).
Table 4 RR for chronic pain in the low back and neck/shoulders at 11-year follow-up according to the combined effect of frequency of sleep
problems and BMI at baseline
Pain location and frequency
of sleep problems
RR (95% CI)
RR (95% CI)
BMI: body mass index
aP-value comparing persons with BMI <25kg/cm2and BMI ?25kg/cm2within each category of sleep problems.
bAdjusted for age (20–29, 30–39,...or ?70 years), physical exercise (none, <1, 1, 2–3, ?4 sessions per week or unknown), psychological well-
being (depressed, somewhat happy, happy or unknown), smoking status (never, former, current or unknown) and occupation (manual,
non-manual, farmer/fisher, non-worker or unknown).
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European Journal of Public Health
systemic inflammation,27–29thereby increasing the susceptibility
for chronic pain. Conversely, physical exercise and maintenance of
normal body weight are associated with a reduced level of systemic
inflammation,28–30providing a possible explanation for our finding
that physical exercise and normal BMI reduce the risk of chronic
pain among persons with mild sleep problems. Although the effect
was only present among those who reported to have sleep problems
‘sometimes’, it is important to note that mild sleep problems
are very common and the number of people at risk of chronic
pain due to sleep problems is high. In the current study, 30% of
the women and 23% of the men reported to have experienced sleep
problems ‘sometimes’ during the past month, which resemble
prevalence rates reported by others. In a study comprising a repre-
sentative sample of British adults, it was found that 14.2% of men
and 19.7% of women suffer from poor sleep on?nights during the
week.31A large-scale study of adults in the USA found that 18–25%
of women and 14–18% of men suffered from sleep problems on ?6
days during the past 2 weeks.32Kronholm et al.33found that 30–35%
of Finnishadults occasionally
symptoms. Given the high proportion of people at risk of chronic
pain due to sleep problems, this is an important target group
for community-based measures aimed at reducing the incidence of
chronic pain in the low back and neck/shoulders. Our results
indicate that such measures should include promotion of regular
physical exercise and maintenance of normal body weight.
The lack of effect among persons who reported sleep problems
‘often/always’, especially for neck/shoulders, may indicate that
chronic pain due to severe sleep problems is less prone to modifi-
cation by lifestyle factors. This may relate to the underlying
mechanism and severity of the sleep problems and should be
investigated in further studies.
The strengths of the current study include the large and unselected
population, the prospective design, the standardized measurement
of height and weight, the exclusion of persons with pain and physical
impairments at baseline as well as exclusion of persons who used
sedative and/or sleeping medicine on a regular basis and the
available information on several potentially confounding variables.
The questions about chronic pain in the low back and neck/
shoulders used inHUNT2 have
validity.14,34The physical exercise questionnaire used in HUNT1
has been validated against measured maximal oxygen uptake in a
random sample of men and found to perform well, with correlation
coefficients ranging from 0.31 to 0.43 for the different measures of
exercise (duration, intensity and frequency).35A limitation of the
study is that biased estimates due to confounding by unmeasured or
unknown factors cannot be ruled out. Moreover, the use of recall of
chronic musculoskeletal pain at HUNT2 to exclude persons with
chronic pain at baseline is a possible weakness. Although reverse
causation is possible, this would have occurred only if women and
men with chronic pain who misclassified their pain duration as <10
years at the HUNT2 survey (despite having actually had chronic
musculoskeletal pain for ?10 years) also were more likely to
report sleep problems at baseline. Unfortunately, we do not have
the data to assess the magnitude of this possible bias. However, it
should also be noted that we also excluded all women and men who
reported having any physical impairment at baseline. The latter is
likely to further increase the probability that women and men with
chronic musculoskeletal pain at baseline were excluded from the
study. Another limitation is that information on physical exercise
and BMI was obtained only at baseline, and changes during the
follow-up period could not be taken into account. Likewise, we
have no information about the progression of sleep problems
during the follow-up period. Furthermore, frequency of sleep
problems was assessed by a single question that did not permit
diagnosis of sleep disorders (e.g. insomnia) according to established
standards.36,37Misclassification of sleep problems is possible,
although it is not likely that such misclassification would have
been differential between persons who developed chronic pain and
suffer from insomnia-related
those who did not. Nevertheless, it is possible that different qualities
of sleep (e.g. sleep duration, sleep disturbances) have different
impact on the risk of chronic pain. Further studies are needed to
determine whether the various qualities of sleep relate differentially
to risk of chronic musculoskeletal pain.
In conclusion, sleep problems are positively and dose-dependently
associated with risk of chronic pain in the low back and neck/
shoulders in adult women and men. An important finding is that
physical exercise and maintenance of normal body weight may
reduce the adverse effect of mild sleep problems on risk of chronic
pain in the low back and neck/shoulder.
The Nord-Trøndelag Health Study (HUNT) is a collaboration
between the HUNT Research Centre (Faculty of Medicine,
Norwegian University of Science and Technology), the Nord-
Trøndelag County Council and the Norwegian Institute of Public
Vik and Lier were supported by grants from the Liaison Committee
between the Central Norway Regional Health Authority (RHA) and
the Norwegian University of Science and Technology (NTNU). Moe
and Bardal were supported by grants from the Faculty of Social
Sciences and Technology Management, Norwegian University of
Science and Technology (NTNU).
Conflicts of interest: None declared.
? Sleep problems are dose-dependently associated with risk of
chronic pain in the low back and neck/shoulders.
? Regular leisure time physical exercise and maintenance of
normal body weight reduce the adverse effect of mild sleep
problems on risk of chronic pain in the low back and neck/
? Community-based measures aimed at reducing the negative
impact of sleep problems on musculoskeletal health should
emphasize the importance of regular exercise and mainten-
ance of normal body weight.
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