Person:

Breakey, Alicia Ann

This dissertation explores the relationships between maternal energetic condition, four bioactive compounds in milk, and infant health and growth outcomes through the lens of human life history theory. Research was conducted among the Toba of Barrio Namqom in Formosa, Argentina. This is among the first of studies to apply a life history biology lens to the dynamics of cortisol, insulin-like growth factor 1 (IGF-1), lactoferrin, and secretory immunoglobulin A (sIgA) in human milk. First, the role of maternal energetic condition as a predictor of the concentration of these four compounds in milk is explored. Several interesting relationships emerge, including significantly lower milk cortisol and IGF-1 among women with higher body mass index, and significantly higher milk cortisol among primiparous mothers. Next, the relationships between infant symptoms of illness and the two milk immunofactors, lactoferrin and sIgA, are investigated. Lactoferrin is found to exhibit a positive association with symptoms of illness, and sIgA shows a negative association. Finally, associations between concentration of milk bioactives and infant growth rate are tested, as well as associations between infant illness and growth rate, and maternal energetic condition and growth rate. Milk IGF-1 is found to positively associate with infant linear growth rate. Maternal parity is found to negatively associate with linear growth rate. First-born status is associated with significantly greater gains in length and mass over a four-month period. These and other results are discussed through the lens of life history biology and avenues for future research at the intersection of life history biology and public health are identified.

Background and objectives: This study aims to better understand the relationship between immune compounds in human milk and infant health. We hypothesized that the concentration of immune compounds in milk would relate to infant illness symptoms according to two possible theoretical paradigms. In the ‘protective’ paradigm, high concentrations of immune compounds prevent infant illness. The converse, the ‘responsive’ framework, posits that concentrations of immune compounds are elevated in response to infection. Methodology: Milk samples (n = 110) and illness data were collected among the Toba of Argentina from 30 mother–infant dyads. Samples were assayed for two immune proteins, lactoferrin and secretory immunoglobulin A (sIgA). Generalized estimating equations were used to assess the relationship between immune composition of milk and symptoms of illness in infants. Results: Lactoferrin was positively associated with symptoms of illness in infants (odds ratios >1), both in the month preceding the sample collection and the subsequent month. sIgA was negatively associated with symptoms (odds ratios <1) in the preceding and subsequent months, an association which was particularly strong for gastrointestinal symptoms. Conclusions and implications: The two compounds investigated in our study had opposite relationships with symptoms of illness; the positive relationship between lactoferrin and illness lends support to our ‘responsive’ paradigm, and the negative relationship between sIgA and symptoms of illness was consistent with our ‘protective’ framework. That elevated lactoferrin is restricted to periods of illness suggests that there may be a cost to mother or infant associated with persistently elevated lactoferrin that is not incurred with elevated sIgA.