Motivation

Breastfed infants tend to be healthier than non-breastfed infants because mother's milk nourishes and protects infants from malnutrition and infectious diseases. Yet, there are large inequalities in the rates of malnutrition and infectious mortality among the breastfed infants particularly in places where food availability is unstable. This motivated us to study if, and how, human milk contents may differ between mothers with different nutritional status and infant age and/or sex.

 What we did

We used breast milk samples stored at ultra-low-temperatures, originally donated by mothers in northern Kenya during the 2006 Horn-of-Africa drought. People in this arid region of the world have maintained their nourishment and health through pastoralism (livestock-based economies) for centuries, or more recently by combining pastoralism with agriculture. During recent decades, this region has experienced increasingly unpredictable rainfall patterns causing droughts, livestock losses, crop failures, and resulting food shortages.

We focused on three types of milk contents: energy (estimated from protein, fat, and lactose contents), folate (vitamin B9), and secretory immunoglobulin A (sIgA) antibodies. We focused on these contents because they are important for infants' nourishment (energy and folate) or resistance against infectious diseases (sIgA), and because these contents preserve well for years or decades frozen at ultra-low temperatures. We also assessed maternal folate status using blood samples that came with milk samples. We also had information on multiple aspects of these mothers' nutrition, including protein-energy (arm/body mass), vitamin A, and iron nutrition. At the start of the project, we expected that maternal malnutrition would generally impair maternal delivery of nutrient/immune contents to milk and therefore we should see malnourished mothers to have decreased milk contents.

In our laboratory, we measured protein, lactose, folate, and sIgA levels in milk, and homocysteine in blood (to determine maternal folate deficiency). We then applied statistics to test the relationships between maternal nutrition, infant age/sex, and milk contents. Statistics allowed us to take into account other things that might influence milk contents (e.g. maternal age) and determine if the relationships were significant (i.e. meaningful and not by chance alone).

 What we found

Contrary to our expectation of general decreases in milk contents, we found that maternal malnutrition was associated with increase, decrease, or no change, depending on the milk content, infant age, and/or sex. Milk energy tended to be resilient against the impact of maternal malnutrition; we saw only subtle or no decreases in milk energy in association with maternal malnutrition. This resilience did not hold among some mothers, however. Namely, vitamin A deficient mothers raising older infants (e.g. > 6 months) delivered substantially lower milk energy contents than did their vitamin A deficient counterparts raising younger infants.

Similarly, milk folate tended to be resilient against decreases in the presence of maternal malnutrition; data even indicated increases in milk folate associated with maternal folate deficiency. Infant characteristics also had important inputs to this. While folate deficient mothers tended to have higher folate contents in milk than their folate sufficient counterparts, within each group, milk folate decreased as infant age advanced. Furthermore, folate deficient mothers delivered higher folate contents to milk for sons than daughters, while sex difference was not noticeable in mothers without folate deficiency.

In contrast, sIgA appeared to decrease in the presence of maternal malnourishment, particularly vitamin A deficiency and low protein-energy nutrition. Here again, infant age and sex had important inputs. Among vitamin A deficient mothers, milk sIgA contents were lowest for younger infants and increased as infant age advanced, while vitamin A sufficient mother delivered more or less stable levels of sIgA regardless of infant age. In addition, mothers with low protein-energy nutrition gave more sIgA to milk for daughters, while mothers having superior protein-energy nutrition gave more sIgA to sons.

 Contributions to society

Our findings contribute to our understanding of how mothers nourish and protect their young in challenging times and places. Our data indicate that mothers facing nutritional stress may be able to maintain normal, or even increased, delivery for some milk contents (e.g. energy, folate) but not others (e.g. sIgA), while infant age and/or sex influence the magnitude of increase/shortfall due to nutritional stress. All this may translate into different levels of milk benefits for the breastfed infants, which may in turn contribute to the large inequalities in the rates of malnutrition and infectious mortality among the breastfed infants in food insecure environments. This understanding is relevant for all of us because the issues of food availability/accessibility and maternal malnutrition (especially covert ones e.g. vitamin/iron deficiencies and anemia) are widespread across the world, including the United States.

The support from NSF allowed this project to employ female students to engage in scientific research with relevance to global health at Michigan State University. This contributes to our nation's effort to increase the participation of women in science.

Last Modified: 01/23/2019
Modified by: Masako Fujita