Several cross-sectional studies have reported an inverse association between the number of hours of sleep and body weight or body mass index (BMI). However, the few prospective studies that have investigated this issue have reported inconsistent results. Stranges et al. therefore examined the cross-sectional and longitudinal relationships between sleep duration and changes in body weight, evaluated with BMI, and body fat distribution, evaluated with waist circumference. The analyses were performed using the Whitehall II Study, a prospective cohort of 10,308 white-collar British civil servants 35-55 years of age in 1985-1988. Similar to previous cross-sectional analyses, the authors found an inverse association between duration of sleep and both BMI and waist circumference. In comparison with 7 hours of sleep, sleep duration of less than or equal to 5 hours was associated with higher BMI and waist circumference as well as an increased risk of obesity. However, in prospective analyses, short sleep duration was neither associated with significant changes in BMI or waist circumference nor with the incidence of obesity. Accordingly, these results do not support a temporal relationship between short sleep duration and future changes in measures of body weight and central adiposity. Instead, they suggest that short sleep duration might represent a risk marker rather than a causative risk factor for obesity.
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