Original ArticleSleep duration and central obesity in women – Differences between short sleepers and long sleepers☆,☆☆
Introduction
Over the past decades sleep duration has decreased [1], [2], [3] and, parallel to this, there has been an increase in the prevalence of obesity [4]. Several studies have found relationships between the two conditions [5], [6], [7], [8], [9], [10], [11]. Inverse relationships between self-reported sleep duration and obesity as well as U-shaped relationships have been found in both men and women [12], [13]. Moreover, short sleep duration is also reported to predict weight gain and obesity later in life [6], [8]. In earlier studies the focus has primarily been on sleep duration in relation to general obesity [5], [6], [7], whereas the association with central obesity is less clear. Central obesity is a stronger risk factor than body mass index (BMI) for both cardiovascular disease and type 2 diabetes mellitus [4], [14], [15]. Further, there may be differences in factors related to central obesity in short sleepers versus long sleepers [16], [17], [18].
In a previous study in women we found an inverse relationship between objectively measured sleep duration and central obesity [19]. This study included 400 women from a population-based sample. Therefore, we wanted to investigate the relationship between sleep duration and central obesity in a larger population and also assess if there are different factors associated with central obesity in short sleepers compared to long sleepers. We hypothesized that both short and long sleep duration was related to central obesity and that there may be differences between the groups in factors related to central obesity. We further hypothesized that there may be differences between younger and older women. Consequently, the aim of this study was to analyze associations between self-reported sleep duration and central obesity and also to assess different factors in relation to central obesity in short and long sleepers in a population-based sample of women.
Section snippets
Methods
In this population-based study (“Sleep and Health in women”) [20], a questionnaire on sleeping habits and somatic disorders was sent to women aged ⩾20 years, randomly selected from the population registry of the city of Uppsala, Sweden The response rate was 71.6% (n = 7051). The final study population included the 6461 non-pregnant women who had reported their sleep duration and waist circumference.
The questionnaire consisted of 109 questions and has previously been described in detail [20].
Statistical analyses
Statistical analyses were performed using Stata 10 (Stata Corporation, College Station, TX, USA). Univariate analyses were conducted using the unpaired t-test for continuous variables and the chi-squared test for categorical variables to compare the sleep duration groups. All significant variables from the univariate analyses were then entered into a multiple model, which was performed using logistic regression with central obesity as a dependent variable. The results from the logistic
Results
Compared with normal sleepers (6–<9 h), both short sleepers and long sleepers were more centrally obese and had greater neck and waist circumference and short sleepers were even more centrally obese than long sleepers. Both short and long sleepers were more physically inactive, more likely to be smokers, had an illness, or were taking medication, and more often suffered from psychological distress compared with normal sleepers. In addition, both short sleepers and long sleepers were more often
Associations with central obesity
Using the squared sleep duration there was a U-shaped relationship between reported sleep duration and waist circumference (p < 0.0001 for comparison with a linear relationship; Fig. 1). Also this relationship remained when adjusting for confounders (p = 0.003 for comparison with a linear relationship; Table 2). A mean difference of six centimeters in waist circumference was seen between women sleeping <5 h and those sleeping 7–<8 h. In addition, there was also a difference of six centimeters between
Discussion
This study showed that there were differences between short sleepers and long sleepers compared to normal sleepers. In addition, we showed a U-shaped association between sleep duration and central obesity. When adjusting for confounders, only the relationship between short sleep and central obesity remained. Furthermore, the association between short sleep duration and central obesity was strongest in younger women.
In unadjusted analyses both short and long sleep duration were associated with
Conflict of interest
The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: http://dx.doi.org/10.1016/j.sleep.2012.06.013.
Acknowledgements
This study was financially supported by the Swedish Heart Lung Foundation and by the Swedish Heart Lung Foundation and the Uppsala County Association against Heart and Lung Diseases.
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Work attributed to: Department of Medical Sciences, Respiratory Medicine and Allergology, Uppsala University, Sweden.
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Funding by: The Swedish Heart Lung Foundation, The Swedish Heart Lung Association and the Uppsala County Association against Heart and Lung Diseases.