Vitamin A dynamics in breastmilk and liver stores: A life history perspective

Objectives: Newborns are dependent on breastmilk vitamin A for building hepatic stores of vitamin A that will become critical for survival after weaning. It has been documented that vitamin A concentrations in breastmilk decline across the first year postpartum in both well‐nourished and malnourished populations. The reason for this decline has been assumed to be a sign of concurrently depleting maternal hepatic stores. This study investigates this assumption to clarify why the decline occurs, drawing on life history theory. Methods: A cross sectional survey was conducted among lactating mothers in Kenya in 2006. Data were used to examine (1) the relationship between liver vitamin A and time, (2) if the relationship between milk and liver vitamin A varies by time, and (3) by maternal parity. Results: The relationship between liver vitamin A and time fits the quadratic pattern with marginal significance ( P = 0.071, n = 192); the liver vitamin A declined during early postpartum then recovered in late postpartum time, controlling covariates. The milk‐liver vitamin A relationship varied by postpartum time periods ( P = 0.03) and by maternal parity ( P = 0.005). Mothers in earlier postpartum or higher parity had a stronger positive relationship between milk and liver vitamin A than mothers in later postpartum or lower parity. Conclusions: Our observations are consistent with life history tradeoffs and negate the assumption that maternal hepatic and milk vitamin A decline together. Rather, maternal liver vitamin A has a dynamic relationship with milk vitamin A, particularly depending on postpartum time and maternal parity. Am. J. Hum. Biol., 2011. © 2011 Wiley‐Liss, Inc.