(P17-058-23) Seasonal and Ambient Temperature-Associated Changes in Human Milk Constituents Among Women in Rural Pakistan

Objectives: Heat stress during pregnancy has been shown to have detrimental effects on obstetric and neonatal outcomes. However, the impact of heat on lactation in humans has not been studied systematically. We examined changes associated with season and ambient temperature in human milk (HM) composition in the immediate post-partum period.

Methods: We conducted secondary analysis from the Women First trial conducted in Thatta, Pakistan where chronic maternal malnutrition and exposure to heat stress are common. HM samples were collected 14 days post-partum (n = 243). Macronutrients and energy were analyzed using the MIRIS analyzer. In a subset of samples (n = 75) quantitative levels of eight B-vitamins, choline and 19 human milk oligosaccharides (HMOs) were assayed via LC-MS or HPLC. Multiple linear regression models were utilized to assess changes in HM components associated with season of birth or average daily maximal temperature (T_max) for the 30-d window prior to sample collection. Temperature data were retrieved from surface monitoring stations for the study period using the GSDOR package.

Results: Concentrations of thiamine, choline, riboflavin, vitamin B12 were influenced by season of birth. Of these levels of thiamine and choline were higher in both the summer and rainy seasons, compared to winter births (p < 0.05). Total solids and energy were higher in summer HM relative to winter collections. Association with ambient temperature showed that total energy, fat and solids were positively associated with ambient temperature. Levels of choline, riboflavin and thiamine were also positively associated with ambient temperature (p < 0.05). Relative to winter HM, levels of two HMOs (3-SL and difucosyllactose) were higher in HM collected in the rainy season (p < 0.05).

Conclusions: Collectively, the findings indicate that in the setting of chronic malnutrition, HM composition was associated with season and ambient temperature. While the studies did not assess milk production the findings are consistent with concentration of HM components associated with lower hydration in summer and greater ambient temperature. Prospective studies are warranted to clarify effects of ambient temperature on milk composition, production and infant growth to identify strategies that support lactation.

Funding Sources: Bill & Melinda Gates Foundation, NIH/NICHD/ODS