Direct and indirect effects of poor sleep quality on body mass index and waist circumference in a female population-based study in Southern Brazil.

OBJECTIVE This study aimed to investigate the direct and indirect effects of poor sleep quality on body mass index (BMI) and waist circumference (WC), considering behavioral factors as intermediate variables. DESIGN A population-based cross-sectional study design was adopted. Data were collected between February and October 2015. Poor sleep quality was assessed using the Brazilian version of the Pittsburgh Sleep Quality Index (PSQI-BR). Weight, height (used to calculate BMI), and WC were measured using standard protocols. Physical activity, sedentary behavior, and fast food consumption were considered intermediate variables. Non-standardized effects were estimated by path analysis with bootstrapped confidence intervals (CIs). SETTING Urban region of the city of Sao Leopoldo, southern Brazil. PARTICIPANTS Representative sample of 1,117 women aged between 20 and 69 years. RESULTS Poor sleep quality (higher PSQI-BR scores) was significantly associated with low physical activity levels (β = -0.05; 95%CI = -0.09 to -0.01). High physical activity levels were associated with lower BMI (β = -0.21; 95%CI = -0.37 to -0.07) and WC (β = -0.64; 95% CI = -1.00 to -0.30). There was a non-significant direct effect of poor sleep quality on BMI and WC. However, low physical activity showed a significant indirect effect on the association between poor sleep quality and increased WC (β = 0.03; 95%CI = 0.01 to 0.07). CONCLUSION The results indicate that the association between sleep quality and WC is mediated by physical activity. This finding can assist in the development of strategies to prevent and reduce abdominal obesity in adult women.