Infant Growth, Milk Composition, and Maternal Energetics in a High Altitude Environment

Washington University, Saint Louis MO

Investigators

Abstract

For the vast majority of human history, breast milk has been the primary source of nutrients during infancy. Recent research has shown human milk to be a tremendously complex fluid containing a wealth of macronutrients, immune factors and hormonal components, all of which get fed to the baby. Similarly, mothers' milk is incredibly variable, with women in different societies and living situations producing different amounts of many of these components. Despite a growing body of research, there is still much left to understand about how and why milk varies in different ecological circumstances and how these differences may affect the health and growth of infants. This study takes a detailed look at a population which lives in the high altitude environment of the Nubri Valley, Nepal, to investigate how breast milk may be involved in the regulation of infant growth under considerable ecological stress. The project will provide opportunities for undergraduate and graduate student research and training, and facilitate regional health and science education at the study location. Understanding how ecological pressures such as altitude and cold stress influence human milk composition and in turn, infant metabolism and physiological development, may be crucial in understanding the risk factors for overweight and metabolic dysfunction in industrialized and rapidly industrializing populations. It is likely that there has been considerable natural selection on human milk composition given the primary role human milk has during infancy, itself a critical period of selection. Growth factors and metabolic hormones found in milk show significant associations with linear growth, weight gain, fat free mass, and size for age, making milk born hormones and cytokines likely candidates for developmental programming of infant body composition. However, these associations have never been investigated in an ecologically stressed population where environmental selection on infant phenotypes may be severe. This project will investigate associations between ecology, maternal physiology, milk composition, and infant growth and development in 115 mother-infant pairs from nine villages in the Nubri Valley of the Himalayas (Nepal). The population is ethnically Tibetan, with family histories recording occupation in the valley for at least 700 hundreds following immigration from the Tibetan plateau. Villages range in altitude from 7,500-13,100 feet above sea level. Milk samples, metabolic tests, and thermal body scans will be collected at four time points over the first year of infant life. The thermal imaging of mother and child is an innovation which will show differences in body fat patterning. Additionally, interviews of the mothers and anthropometric measurements (height, weight, body composition) of both mother and child will be collected beginning at birth and at two month intervals afterward. The resulting data will provide the most complete picture ever collected of altitude- and seasonality-associated differences in growth, milk hormones, and maternal reproductive condition across the first year of life.