Direct and indirect effects of poor sleep quality on BMI 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 BMI and waist circumference (WC), considering behavioural 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 behaviour and fast food consumption were considered intermediate variables. Non-standardised effects were estimated by path analysis with bootstrapped CI. Setting: Urban region of the city of Sao Leopoldo, southern Brazil. Participants: Representative sample of 1117 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, –0·01). High physical activity levels were associated with lower BMI (β = –0·21; 95 % CI –0·37, –0·07) and WC (β = –0·64; 95 % CI –1·00, –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, 0·07). Conclusions: 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.