The role of physical activity in the prospective association between body mass index and depressive symptoms in mothers from the 2015 Pelotas (Brazil) Birth Cohort

Maternal obesity has been associated with postpartum depression and a protective role of physical activity is indicated. This study aims to examine the role of moderate and vigorous physical activity (MVPA) in the prospective association between body mass index (BMI) and depressive symptoms in a cohort of mothers. Depressive symptoms were assessed at 3 and 48 months postpartum using the Edinburgh Depression Scale. BMI was calculated from weight and height measurements at 24 months postpartum and self-reported pre-pregnancy weight. MVPA was measured by accelerometers at 12–16 weeks of pregnancy and 24 months postpartum. Accelerometry data were available for 1953 mothers in pregnancy and 2546 postpartum. BMI was not significantly associated with depressive symptoms. However, the relationship between pre-gestational BMI and depressive symptoms 3 months postpartum was moderated by MVPA (p = 0.04). Among mothers with low MVPA, the association between BMI and depressive symptoms was not significant. However, among those who performed ≥42 min of MPVA/day, the relationship became significant and inverse (β: −0.125; 95 %CI: −0.248; −0.001), with mothers with higher BMI and high MVPA having lower depressive symptom scores. In conclusion, MVPA performs a positive role in the association between BMI and depressive symptoms, reinforcing the importance of MVPA promotion among mothers.