Background: Although previous studies showed the long-term effects of sleep duration on risk of weight gain, Western tends to gain weight irrespective of sleep duration over a long period. Conversely, it is showed that body mass index (BMI) decreases during a long period in Japanese and thus, the long-term effect of sleep duration on weight gain and obesity is still unclear in Asia. Methods: We followed up 13,629 participants aged 40-79years and prospectively collected data from 1995 to 2006. We divided the participants into five groups according to their self-reported sleep duration: <5h (short sleep), 6h, 7h (reference), 8h, and >9h (long sleep). The main outcome was >5kg weight gain or BMI>25kg/m2 (obesity). We used logistic regression analyses to derive odds ratios (ORs) and 95% confidence intervals (CIs), adjusted for several confounding factors. Results: We observed no association between sleep duration and risk of >5. kg weight gain and obesity. After stratification by BMI, long sleepers had a significantly increased risk of >5. kg weight gain (OR: 1.36, 95%CI: 1.09-1.70) in obese participants. Conclusions: Among community-dwelling Japanese, only obese long sleepers have a significantly increased long-term risk of >5. kg weight gain.
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