With NSF support, Dr. Chris Kuzawa and an international team based out of Northwestern University, the University of North Carolina, Chapel Hill, and the University of San Carlos, Cebu City (the Philippines), will investigate whether fetal and infant nutrition and growth influence male reproductive biology, as measured in roughly 1,000 young adults participating in a long-term study of health in the Philippines. Specifically, they will test the hypothesis that undernutrition prior to birth (as indicated by birth weight or maternal pregnancy nutrition) or during the months after birth (as indicated by mode of infant feeding or growth rate) will predict reduced testicular function, including lower production of testosterone and other hormones that are correlated with male fecundity. In addition, this project will also investigate the broader health effects of any changes in testosterone, such as reductions in muscle, strength or changes in blood pressure. The rationale for this series of questions comes from recent research showing similar long-term effects of early life undernutrition on these traits in rats and sheep. To date, no large scale test of these relationships have been conducted in humans.
This study is uniquely equipped to explore these relationships, because all of the participants were first enrolled in the study when their mothers were pregnant with them (in 1983). Birth size, growth rate, nutrition and other important characteristics were monitored periodically as each person aged, providing a rich record of their life experiences. These individuals are now 22 years of age, allowing this study to evaluate if nutrition and growth measured early in life predict reproductive function and health measured several decades later in adulthood.
To answer this study's specific hypotheses, these data will be augmented by adult information on lifestyle and diet measured in interviews, and biological specimens (blood and saliva) for the measurement of reproductive hormones. All of these supplemental data and specimens were recently collected using a protocol designed to address this study's research goals, and the specimens are now in freezer storage at Northwestern University. NSF funding will only be required to cover the costs of analyzing hormones in these samples, which will be measured in the Laboratory for Human Biology Research housed in the Department of Anthropology at Northwestern University.
This study promises significant insights into an issue of considerable theoretical and applied importance. As is true for females, cross-cultural research has documented a great deal of population variation in male reproductive function. However, unlike in females, this biological variability has been difficult to explain in males. This study will address this paradox by investigating whether differences in early life nutrition and growth influence male reproduction function. The answer to this question may also provide insights into an important mode of human adaptation: reducing expenditure on "costly" traits, such as reproduction and muscle mass, might be a necessary (if less than ideal) response when faced with a challenging nutritional environment.
The broader impacts of this study include training opportunities for both graduate and undergraduate students interested in gaining experience with laboratory research. It will also strengthen the collaborative ties between an international team of researchers based in the US and the Philippines, who share interests in understanding the causes and consequences of male fertility.
