Short sleep and obesity in a large national cohort of Thai adults

Objective: To investigate the relationship between short sleep and obesity among Thai adults. Design: Both 4-year longitudinal and cross-sectional analyses of a large national cohort. Setting: Thai adults residing nationwide from 2005 to 2009. Participants: Cohort members were enrolled as distance learners at Sukhothai Thammathirat Open University (N=87 134 in 2005 and 60 569 at 2009 follow-up). At 2005 baseline, 95% were between 20 and 49 years of age. Measures: Self-reported sleep duration was categorised as <6, 6, 7, 8 and ≥9 h. For all analyses (2005 and 2009 cross-sectional and 2005-2009 longitudinal), we used multinomial logistic regression models to assess the effect of sleep duration on abnormal body size (underweight, overweight-at-risk, obese). Results were adjusted for an array of relevant covariates. Results: At the last cohort follow-up in 2009, crosssectional associations linked short sleep (<6 h) and obesity: adjusted ORs (AOR) =1.49, 95% CIs 1.32 to 1.68 for women and AOR=1.36, 95% CI 1.21 to 1.52 for men. The earlier cross-sectional baseline results in 2005 were quite similar. Longitudinal analysis (2005-2009) of 4-year incremental weight gain (5 to <10%, 10 to <20% and 20%+) strongly supported the short sleepeobesity relationship (significant AORs of 1.10, 1.30 and 1.69, respectively). Conclusions: The results are internally consistent (2005 and 2009) and longitudinally confirmatory of a short sleep effect on obesity among Thai adults. Further research is needed to elucidate causal mechanisms underlying the sleepeobesity relationship.