Sleep duration and weight change in midlife women: the SWAN sleep study

Short sleep duration has been associated with higher current BMI and subsequent weight gain. However, most prior longitudinal studies are limited by reliance on self-reported sleep duration, and none accounted for the potential confounding effect of sleep-disordered breathing. The associations of sleep duration with current BMI and BMI change were examined among 310 midlife women in the Study of Women's Health Across the Nation (SWAN) Sleep Study (2003-2005).

Sleep duration was assessed for approximately one month with concurrent wrist actigraphy and sleep diaries. The presence and severity of sleep-disordered breathing was quantified using the apnea-hypopnea index (AHI) based on in-home polysomnography. BMI was assessed annually through core SWAN visit 10 (2006 and 2008).

Mean BMI increased from 29.6 (SD = 7.8) kg/m(2) to 30.0 (SD = 8.0) kg/m(2) over an average of 4.6 years (SD = 1.0) of follow-up. In cross-sectional analyses controlling for AHI, demographic variables, and several potential confounding variables, actigraphy (estimate = -1.22, 95% confidence interval (CI): -2.03, -0.42) and diary (estimate = -0.86, 95% CI -1.62, -0.09) measures of sleep duration were inversely associated with BMI. Each hour of less sleep was associated with 1.22 kg/m(2) greater BMI for actigraphy sleep duration, and a 0.86 kg/m(2) greater BMI for diary sleep duration. Longitudinal associations between sleep duration and annual BMI change were nonsignificant in unadjusted and fully adjusted models.

In this cohort of midlife women, cross-sectional associations between sleep duration and current BMI were independent of sleep-disordered breathing, but sleep duration was not prospectively associated with weight change.