Abstract
BackgroundStudies of Western populations have shown an inconsistent longitudinal association between short sleep duration and change in body mass index (BMI); a recent Japanese cohort study reported a significant association in men, but over a 1-year period. The aim of this longitudinal study was to examine whether this association was robust over a 4-year interval in Japanese men.MethodsA total of 3803 middle-aged Japanese male white-collar workers (mean age 47.8 years, mean BMI 23.9 kg/m2) in Tokyo, Japan, were included in this study from 1994–1995 (baseline) to 1998–1999 (follow-up). Height and weight were objectively measured at annual health checkups, and other data, including sleep duration, were collected using a structured interview. We used linear regression models to estimate change in BMI, after adjustment for covariates. The reference category for sleep duration was set to 7 hours, to conform with previous studies.ResultsAs compared with participants sleeping 7 hours, those sleeping 5 hours or less had a significantly higher BMI at baseline (beta coefficient: 0.34 kg/m2, 95% confidence interval (CI): 0.03, 0.65) and gained 0.15 kg/m2 in BMI over 4 years (95% CI: 0.03, 0.27), after adjustment for age, baseline BMI, lifestyle behavior, and medication.ConclusionsThe longitudinal association between short sleep duration at baseline and relative increase in BMI was significant in Japanese male workers over a 4-year interval.
Highlights
Short sleep duration (5 hours of sleep or less) has been suggested as a risk factor for obesity in adults, the association between sleep duration and obesity has been criticized as spurious owing to weaknesses in study designs, small sample sizes, and the use of self-reported measurements of body weight and height.[1,2,3,4,5,6,7,8,9] recent longitudinal studies have successfully overcome the design weaknesses of earlier studies, the findings remain controversial
If a larger coefficient were observed after a 4-year interval, it would support the hypothetical link between short sleep duration and increased body mass index (BMI) among Japanese male workers
Abbreviation: BMI, body mass index. aData are presented as means or percentages. bStatistical significance was assessed by analysis of variance for continuous variables and by the chi-square test for categorical variables. cΔWeight was calculated by subtracting weight at baseline from weight at follow-up. dΔBMI was calculated by subtracting BMI at baseline from BMI at follow-up
Summary
Short sleep duration (5 hours of sleep or less) has been suggested as a risk factor for obesity in adults, the association between sleep duration and obesity has been criticized as spurious owing to weaknesses in study designs, small sample sizes, and the use of self-reported measurements of body weight and height.[1,2,3,4,5,6,7,8,9] recent longitudinal studies have successfully overcome the design weaknesses of earlier studies, the findings remain controversial. A long-term followup study by Patel et al found that the relative increase in mean weight change in short sleepers was greatest after a 4-year interval, during a total follow-up period of 16 years.[6] Thanks to the inclusion of a very large cohort, Watanabe et al successfully identified a significant, yet very small, beta coefficient (0.013 kg/m2 per year)[11] over a 1-year observation period. Studies of Western populations have shown an inconsistent longitudinal association between short sleep duration and change in body mass index (BMI); a recent Japanese cohort study reported a significant association in men, but over a 1-year period. The aim of this longitudinal study was to examine whether this association was robust over a 4-year interval in Japanese men. Conclusions: The longitudinal association between short sleep duration at baseline and relative increase in BMI was significant in Japanese male workers over a 4-year interval
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