Doctoral Dissertation Improvement: An Evolutionary Perspective on Mother-Offspring Vitamin A Transfer

University Of Washington, Seattle WA

Investigators

Abstract

Vitamin A (VA) is an essential micronutrient that humans must consume because we cannot synthesize it in our body. It is vital particularly for normal vision and immune responses. Globally, 21% of children are estimated to have VA deficiency (VAD) and suffer increased rates of death from diarrhea, measles, and malaria. Newborns have meager VA stores, and are dependent on breastmilk for immediate physiological needs and for building liver stores needed after weaning. VAD mothers produce breastmilk with low VA, potentially compromising their children's VA status. It has been documented that VA concentrations in breastmilk decline across the first year postpartum in women from both developed and developing nations, but the reason for decline has been left uninvestigated and simply assumed to be a sign of depleting maternal liver stores. However, studies indicate that the decline may occur even in mothers with adequate liver stores. The project will address why breastmilk VA concentrations decline despite potentially negative health effects on the breastfed child. It will do so from a biocultural anthropological perspective, consisting of two tiers: the first tier focuses on the basic biology of VA transfer, and the second tier examines the role of cultural, environmental, and socioeconomic factors. In the first tier, we test hypotheses derived from life history theory, viewing the decline in milk VA as a manifestation of an evolved maternal reproductive strategy via physiological reallocation of VA between breastmilk, maternal survival, and future reproduction, depending on the time since birth of the child. To this end, data on dietary intake, breastmilk VA, maternal liver VA levels, and correlates will be collected from lactating women. In the second tier, other individual-, household-, and community-level variables, collected through a combination of survey, interview and observations, will be examined for their links to the biological parameters. The study population is Ariaal women of Marsabit District, Kenya, where our pilot project suggests the presence of mothers with varied VA status, spanning from VA replete, subclinical VAD, to clinical VAD, as well as VA supplemented mothers within a single population. Intellectual merit of the project includes a better understanding of mother-child VA transfer with a focus on the maternal side. A large body of literature exists in public health documenting the nutrient content of breastmilk, and factors affecting its variation. However, this literature focuses on the consequences for infant growth and health, with an inherent assumption that interests of mother and offspring coincide: maximum growth and health of the offspring. However, an evolutionary perspective negates this assumption with the notion of maternal strategies, in which the mother may prioritize her survival and future reproduction over the needs of her existing offspring. This perspective may shed light on the seemingly paradoxical variation in mother-offspring VA transfer. The project has broader significance for effective intervention. It will identify community-specific etiology of maternal VAD, with implications for culturally appropriate dietary recommendations for the Ariaal community. Further, it will provide a scientific understanding of maternal allocation of VA between the liver and breastmilk across the first postpartum year, crucial for improving VA supplementation programs. If the decline in breastmilk VA is an evolved human trait, lower-dose pre-pregnant supplementation might be preferred over the current approach of high-dose, postpartum supplementation. Since VAD is associated with mother-to-child transmission of HIV, this is particularly important in the context of the HIV/AIDS pandemic.