Ambient temperature and exclusive breastfeeding: a nationwide cohort study in Brazil.

BACKGROUND: The climate crisis presents an emerging global challenge with potential implications for breastfeeding. We estimated the association between ambient temperatures (both heat and cold) and interruption of exclusive breastfeeding (EBF) in a nationwide cohort in Brazil. METHODS: The population-based longitudinal study was conducted using data from the Food and Nutrition Surveillance System (SISVAN-Web) between 2015 and 2019. EBF was defined as the consumption of breast milk only on the day of the visit, with no intake of any other liquids or foods. Daily minimum and maximum ambient temperatures and relative humidity were derived from the Brazilian Daily Weather Gridded Data (BR-DWGD). The association between ambient temperature and time to interruption of EBF was assessed using Cox proportional hazards models combined with distributed lag non-linear models (DLNMs). RESULTS: A total of 397 239 children aged 0 to <6 months were included in the study. Nationally, low temperatures were not significantly associated with EBF interruption (hazard ratio [HR] 1.01, 95% confidence interval [CI] 0.98-1.05), whereas heat exposure was associated with a 10% higher risk (HR 1.10, 95% CI 1.08-1.14). The increased risk associated with heat exposure was similar across infant age groups, child sex, and levels of municipal material deprivation. In contrast, we found no association between cold temperatures and EBF interruption at the national level. However, our findings suggest that cold-related effects may differ across infant age and municipal deprivation levels. CONCLUSION: Our findings highlight the importance of strengthening breastfeeding support during periods of elevated heat and integrating climate-sensitive approaches into maternal and child health policies.