Association between sleep duration, weight gain, and obesity for long period

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 40-79 years and prospectively collected data from 1995 to 2006. We divided the participants into five groups according to their self-reported sleep duration: <= 5 h (short sleep), 6 h, 7 h (reference), 8 h, and >= 9 h (long sleep). The main outcome was >= 5 kg weight gain or BMI >= 25 kg/m(2) (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. (C) 2012 Elsevier B. V. All rights reserved.