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Keywords:

  • follow-up;
  • men;
  • sleep duration;
  • sleep problems;
  • weight gain;
  • women

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgements
  9. Conflicts of interest
  10. References

The objective of this study was to examine the associations of sleep duration with subsequent weight and major weight gain in women and men during a follow-up period of 5–7 years. The data were derived from the Helsinki Health Study cohort mail questionnaire surveys among 40–60-year-old employees of the City of Helsinki, Finland. At baseline in 2000–2002, 8960 people responded to the survey (80% women, response rate 67%). The follow-up survey was conducted in 2007 among all respondents to the baseline survey (n = 7332, response rate 83%). Sleep duration (5 h or less up to 10 h or more) and weight and weight gain of at least 5 kg were based on self-reports. Analyses of variance and logistic regression analyses were used to examine the associations between sleep duration and weight, as well as major weight gain. Short sleep duration was associated with major weight gain [odds ratio (OR) 1.52; 95% confidence interval (CI) 1.08, 2.14] during the follow-up. Adjusting for several covariates had only minor effects on that association. Long sleep duration was associated with major weight gain after adjusting for age (OR 1.35; 95% CI 1.00–1.81). No associations were found among men. Sleep duration was associated with major weight gain among middle-aged employed women. Short sleep may be a risk factor for subsequent weight gain.


Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgements
  9. Conflicts of interest
  10. References

The prevalence of obesity has increased worldwide (WHO, 2000), including in Finland (Vartiainen et al., 2009). Sleep duration has slightly decreased and prevalence of short sleepers increased (Kronholm et al., 2008). Short sleep has also increased among full-time workers (Knutson et al., 2010). The question has been raised as to whether short sleep duration might be associated with obesity and weight gain, and cross-sectional studies have revealed an association with obesity (Bjorvatn et al., 2007; Singh et al., 2005). A recent meta-analysis confirms that cross-sectional studies consistently show an increased risk of obesity among short sleepers (Cappuccio et al., 2008). Several longitudinal studies have examined the associations of sleep duration with obesity and weight gain, but the results are inconsistent (Chaput et al., 2008; Gangwisch et al., 2005; Hasler et al., 2004; Lauderdale et al., 2009; López-García et al., 2008; Patel et al., 2006; Stranges et al., 2008; Watanabe et al., 2010). There is evidence that both short and long sleep duration are associated with weight gain (Chaput et al., 2008; López-García et al., 2008), some studies reporting an association among women only (López-García et al., 2008) and others among men only (Watanabe et al., 2010). According to one review, short sleep duration is inconsistently associated with an increased risk of subsequent obesity among adults (Nielsen et al., 2010). In that review, the authors suggested that the association between short sleep duration and weight gain might be bidirectional, i.e. short sleep is associated with weight gain and weight gain with short sleep. There are a number of cross-sectional studies linking sleep duration and weight, but there are less large-scale longitudinal studies, and further investigation is needed in order to clarify the association between sleep duration and weight gain among adults.

We have previously examined the association between sleep problems and weight gain (Lyytikäinen et al., 2010). This study is focused on the associations of sleep duration with weight and major weight gain over a 5–7-year follow-up period among middle-aged women and men. Although sleep duration and sleep problems are connected to each other (Grandner and Kripke, 2004), both indicate important but different issues of sleep, as emphasised in previous sleep research (Sivertsen et al., 2009). We also aimed to examine to what extent such associations are independent of a number of covariates. Determinants of sleep and weight commonly used in previous studies were included: age; body mass index (BMI; Watanabe et al., 2010); physical activity (Patel et al., 2006); health behaviours (López-García et al., 2008); marital status (Cournot et al., 2004); education (Gangwisch et al., 2005); work arrangements (Chaput et al., 2008); sleep problems (Gangwisch et al., 2005); and common mental disorders (Stranges et al., 2008).

Materials and Methods

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgements
  9. Conflicts of interest
  10. References

The data source was the Helsinki Health Study mail questionnaire surveys among 40–60-year-old employees of the City of Helsinki, Finland. At baseline in 2000–2002 a total of 8960 persons responded to the survey (80% women, 20% men; Lahelma et al., 2005). The gender distribution reflects the distribution of women and men among employees of the City of Helsinki. The overall survey response rate was 67% (women 69%, men 60%). A follow-up survey was conducted in 2007 among all respondents to the baseline survey (n = 7332, response rate 83%). We excluded those who were pregnant, did not know if they were pregnant and those with missing data on pregnancy (n = 61), and those with missing data on weight or height (n = 120) and sleep duration (n = 124). The final sample comprised 7027 respondents (5729 women, 1298 men).

The respondents were asked how many hours per night on average they slept during the week. The response alternatives were: 5 h or less; 6; 7; 8; 9; and 10 h or more. Given the small numbers involved, we collapsed the final two alternatives. Sleep duration of 7 h was used as the reference category in the analyses.

Weight was self-reported both at baseline and follow-up. Following the World Health Organization and the Food and Agriculture Organization (WHO/FAO, 2003) recommendations, weight gain of at least 5 kg during the follow-up was considered major weight gain.

Covariates measured at baseline included age, BMI, physical activity, current smoking, alcohol consumption, marital status, education, work arrangements, sleep problems and common mental disorders, and these variables were included in models 1–6 in addition to sleep duration. Physical activity was measured by approximate metabolic equivalent tasks (METs; Kujala et al., 1998) and was classified into four categories: which were inactive (under 14 MET-hours per week); active moderate (14–30 MET-hours per week); very active moderate (30–50 MET-hours per week); and conditioning (over 50 MET-hours per week; Lahti et al., 2010). Alcohol consumption was measured by weekly consumption of beer, wine and hard liquor, and classified into four categories: not at all; <4 portions per week; 4–16 portions per week; and 16 or more portions per week on average (Salonsalmi et al., 2009). Marital status was classified as unmarried, cohabiting/married and divorced/widowed. Educational level was classified into three categories: basic; intermediate; and higher education. Work arrangements included regular daytime work, shift work without night shifts, and shift work with night shifts. Sleep problems were measured by the four-item Jenkins Sleep Questionnaire, asking about difficulties initiating and maintaining sleep, and non-restorative sleep during the previous 4 weeks (Jenkins et al., 1988). Common mental disorders were measured by the 12-item General Health Questionnaire (GHQ-12; Goldberg et al., 1997). The summary score varied from 0 to 12, and was dichotomised into those without (scores 0–2) and those with (scores 3–12) common mental disorders following previous recommendations (Goldberg et al., 1997). The covariates included are described in detail elsewhere (Lyytikäinen et al., 2010).

First, we used analyses of variance to calculate the average age-adjusted weight in kilograms by the length of sleep duration, and logistic regression analysis in order to examine the associations between sleep duration at baseline and subsequent weight gain at follow-up. The results are presented as odds ratios (OR) and their 95% confidence intervals (CI). Model 1 included age, and model 2 age and baseline BMI as continuous variables. Building on model 2, model 3 also included baseline physical activity, current smoking and alcohol consumption, model 4 marital status, education and work arrangements, model 5 sleep problems, and model 6 common mental disorders. Version 15.1 of the Statistical Package for the Social Sciences (spss) was used for the analyses [SPSS (IBM), Chicago, IL, USA].

Results

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgements
  9. Conflicts of interest
  10. References

The association between sleep duration and weight (kg) at both baseline and follow-up tended to be U-shaped among women, whereas among men there were only slight indications of a U-shaped association (Table 1). Weight gain during the follow-up was greatest (3.4 kg; 95% CI 2.5, 4.2) among women with short sleep duration (5 h or less), but it did not differ by sleep duration among men.

Table 1.   Weight (kg) at baseline and at follow-up, and weight change during the follow-up by sleep duration among women and men, adjusted for age
Sleep durationnBaseline (kg) [CI 95%]Follow-up (kg) [CI 95%]Weight gain during follow-up (kg) [CI 95%]
  1. CI, confidence interval.

Women
 5 h or less17068.8 [67.0, 70.7]72.2 [70.2, 74.2]+3.4 [2.5, 4.2]
 6 h112269.1 [68.4, 69.8]70.8 [70.0, 71.6]+1.7 [1.4, 2.0]
 7 h268568.3 [67.8, 68.8]70.3 [69.7, 70.8]+2.0 [1.5, 2.1]
 8 h152767.6 [67.0, 68.2]69.4 [68.7, 70.1]+1.8 [1.5, 2.1]
 9 h or more22570.5 [68.8, 72.1]72.5 [70.8, 74.3]+2.0 [1.4, 2.8]
 Total572968.3 [68.0, 68.7]70.3 [69.9, 70.6]+2.0 [1.8, 2.1]
Men
 5 h or less5485.4 [81.8, 88.9]86.6 [82.8, 90.4]+1.2 [−0.3, 2.8]
 6 h30785.3 [83.8, 86.8]87.1 [85.5, 88.7]+1.8 [1.1, 2.4]
 7 h67082.6 [81.6, 83.6]83.8 [82.8, 84.9]+1.2 [0.8, 1.7]
 8 h22783.3 [81.6, 85.1]83.8 [82.0, 85.7]+0.5 [−0.3, 1.2]
 9 h or more4084.6 [80.5, 88.7]86.3 [81.9, 90.8]+1.7 [−0.3, 3.5]
 Total129883.5 [82.8, 84.3]84.8 [84.0, 85.6]+1.3 [0.9, 1.6]

Adjusting for age (Table 2), women with sleep duration of 5 h or less (OR 1.52; 95% CI 1.08, 2.14.) and 9 h or more (OR 1.35; 95% CI 1.00, 1.81) were more likely to have gained 5 kg or more in weight over the follow-up compared with women with a sleep duration of 7 h (OR 1.00). Adjusting for baseline BMI, sleep duration was still associated with a weight gain of at least 5 kg. Adjusting for the other covariates (models 3–6) had only minor effects on this association. However, the association between long sleep duration and major weight gain (OR 1.35; 95% CI 1.00, 1.81) was slightly attenuated after adjusting for baseline BMI, physical activity, smoking, alcohol consumption, marital status, educational level, work arrangements and common mental disorders, whereas adjusting for sleep problems had no effect (OR 1.35; 95% CI 0.99, 1.83).

Table 2.   The associations between sleep duration and weight gain among women (n = 5729) and men (n = 1298), the odds ratios (OR) and their 95% confidence intervals (CI) from the logistic regression analysis
 Weight gain
Model 1 OR [CI 95%]Model 2 OR [CI 95%]Model 3 OR [CI 95%]Model 4 OR [CI 95%]Model 5 OR [CI 95%]Model 6 OR [CI 95%]
  1. Model 1: adjusted for age.

  2. Model 2: model 1 + baseline BMI.

  3. Model 3: model 2 + physical activity + smoking + alcohol consumption.

  4. Model 4: model 2 + marital status + educational level + work.

  5. Model 5: model 2 + sleep problems.

  6. Model 6: model 2 + common mental disorders.

Women
 5 h or less1.52 [1.08, 2.14]1.47 [1.04, 2.08]1.42 [1.01, 2.01]1.46 [1.03, 2.06]1.50 [1.05, 2.13]1.42 [1.01, 2.01]
 6 h1.05 [0.89, 1.23]1.02 [0.87, 1.20]0.99 [0.84, 1.17]1.01 [0.86, 1.19]1.00 [0.85, 1.18]1.01 [0.85, 1.19]
 7 h1.001.001.001.001.001.00
 8 h0.96 [0.83, 1.11]0.97 [0.84, 1.12]0.97 [0.83, 1.12]0.97 [0.84, 1.13]0.99 [0.85, 1.15]0.97 [0.84, 1.13]
 9 h or more1.35 [1.00, 1.81]1.30 [0.96, 1.75]1.28 [0.95, 1.73]1.30 [0.96, 1.76]1.35 [0.99, 1.83]1.30 [0.97, 1.76]
Men
 5 h or less0.96 [0.49, 1.89]0.89 [0.45, 1.77]0.90 [0.45, 1.81]0.86 [0.43, 1.71]0.90 [0.45, 1.82]0.88 [0.44, 1.74]
 6 h1.29 [0.94, 1.77]1.22 [0.89, 1.68]1.23 [0.89, 1.69]1.19 [0.86, 1.64]1.22 [0.88, 1.69]1.21 [0.88, 1.67]
 7 h1.001.001.001.001.001.00
 8 h0.95 [0.66, 1.38]0.94 [0.65, 1.36]0.96 [0.66, 1.39]0.96 [0.66, 1.39]0.98 [0.67, 1.42]0.95 [0.65, 1.38]
 9 h or more1.04 [0.48, 2.26]1.05 [0.48, 2.29]1.08 [0.49, 2.37]1.01 [0.46, 2.24]1.04 [0.47, 2.27]1.06 [0.48, 2.32]

Similar analyses were conducted among men, but no associations could be confirmed (Table 2).

Discussion

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgements
  9. Conflicts of interest
  10. References

The aim in this study was to examine the associations of sleep duration with weight and major weight gain in a cohort of middle-aged women and men. No associations were found among men. The main finding for women was a longitudinal association between short sleep duration at baseline and subsequent major weight gain at follow-up. The association remained even after several covariates were taken into account. Additionally, there was a tendency for a cross-sectional U-shaped association between sleep duration and weight at baseline and at follow-up.

We found in our previous study within the same cohort that sleep problems were associated with major weight gain (Lyytikäinen et al., 2010). The present study extended the analyses to short sleep duration, which was also associated with weight gain in women. This finding is consistent with the results of other studies (Chaput et al., 2008; López-García et al., 2008; Patel et al., 2006). The underlying mechanisms may include the association between short sleep duration and reduced leptin and elevated ghrelin levels, which tend to increase appetite and through this contribute to weight gain (Taheri et al., 2004). Another possible explanation is that sleeping less may reduce the energy to engage in healthy food habits and sufficient physical activity, and that may prevent successful weight maintenance. However, it was found in a recent study that dietary patterns only partially explained the association between short sleep duration and obesity (Nishiura et al., 2010). It has also been suggested that short sleep duration can modify the amount, composition and distribution of food intake (Nedeltcheva et al., 2009). In a recent study among adolescents, short sleep duration was suggested to change eating patterns (Weiss et al., 2010). Moreover, long sleep duration was associated with major weight gain among women, after adjusting for age. Other studies have reported an association between long sleep duration and weight gain even after adjusting of a number of covariates (Chaput et al., 2008; López-García et al., 2008). A plausible explanation for this could be reduced energy expenditure when staying longer in bed (Chaput et al., 2008; Watanabe et al., 2010). Our study included similar covariates to the Japanese study (Watanabe et al., 2010), which found an association between short sleep duration and weight gain only among men over a 1-year follow-up, and in both studies these associations remained after adjusting for several covariates. The participants in the Japanese study were mostly employed men, whereas most of our subjects were women. There are social and cultural differences between Finnish and Japanese female employees, which might account for the lack of association among Japanese women. López-García et al. (2008) also observed an association between sleep duration and weight gain only in women, but the reasons remain unclear. Unlike Watanabe et al. (2010), we also included sleep problems as a covariate, but neither this nor the other covariates explained the association. Few studies on sleep duration and weight gain (Gangwisch et al., 2005; López-García et al., 2008) control for sleep problems as a potential confounding variable. We suggest that it is vital to take such problems into account given the potential shorter duration of sleep among those affected (Sivertsen et al., 2009).

Our study also suggests a U-shaped association between sleep duration and weight, which we found among women both at baseline and at follow-up, and which is in line with the results of other studies (Gottlieb et al., 2006; Kripke et al., 2002; Taheri et al., 2004). However, as far as men are concerned the association and its shape remain unclear.

Methodological considerations

Both weight and sleep duration were self-reported in our study. Self-reports are known to be prone to bias. Lauderdale et al. (2008) observed in their study that the correlation between self-reported and objective-measured sleep duration was moderate and biased. Also, self-reported weight could lead to bias (Visscher et al., 2006). Our response alternatives only included entire hours, which is a relatively crude classification. Sleep duration was, however, measured both at baseline and follow-up, and we conducted control analyses concerning changes in the sleep duration over the 5–7-year follow-up period (data not shown). In our study sleep duration remained unchanged among half of the participants, which is in accordance with Swedish results on obese patients (Marshall et al., 2010). In the Swedish study, changes in sleep duration were unassociated with weight loss among patients who were severely obese. However, it might be possible that decrease and increase in sleep duration are followed by different changes in weight (Nielsen et al., 2010). Our control analyses suggested that most of the changes in sleep duration occurred from 7 to 8 h or from 8 to 7 h during the follow-up, and that decrease in sleep duration and increase in sleep duration were similarly associated with weight gain (data not shown).

The association between short sleep and weight gain remained only among women sleeping 5 h or less, covering 3–4% of the studied population. Although a relative low prevalence at the population level, nevertheless large numbers of short sleepers are potentially at risk of weight gain.

The results cannot be generalised to all middle-aged women and men given our sample of an occupational cohort of initially employed people. Nevertheless, the workplace concerned employs a large number of women and men in a variety of occupations. The number of men in the data was relatively small, however, and this could have affected the statistical power of the analyses. Non-response at baseline was substantial (33%), but according to our non-response analysis the data were broadly representative of the target population (Laaksonen et al., 2008). The non-response rate at follow-up was much smaller (17%). The strengths of this study include the size of the cohort and the prospective follow-up design. We were also able to include a large number of baseline covariates, including sleep problems and weight and height at two time points.

Conclusion

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgements
  9. Conflicts of interest
  10. References

Our results provide novel evidence of an association between short sleep and subsequent major weight gain among middle-aged employed women. Short sleep duration may be a risk factor for major weight gain.

Acknowledgements

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgements
  9. Conflicts of interest
  10. References

The Helsinki Health Study is supported by the Academy of Finland (grants #1129225, #1121748) and the Finnish Work Environment Fund (grants #107187, #107281). T.L. is supported by the Academy of Finland (grant #133434), the Yrjö Jahnsson Foundation and the Finnish Cultural Foundation. E.L. is supported by the Academy of Finland (grant #1135630). We also thank the City of Helsinki.

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  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgements
  9. Conflicts of interest
  10. References
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