Hormones and Reproduction in the Bolivian Highlands

Kinsey Institute Senior Scientist, Dr. Virginia Vitzthum. Photo by Aaron Bernstein.

Scientist at Work: Virginia Vitzthum

Life is all about tradeoffs, judging prospective investments by their risks and rewards, and an Indiana University evolutionary anthropologist has shown this to be true at the very beginnings of life: When costs outweigh benefits, successful pregnancies are less likely to occur.

Virginia J. Vitzthum, a senior scientist at the Kinsey Institute for Research in Sex, Gender, and Reproduction, and professor in the IU College of Arts and Sciences' Department of Anthropology, has studied pregnancies which are lost early in gestation, within seven weeks after conception. Her research on rural Bolivian women shows that rates of such early pregnancy losses more than double during periods of intense farm labor and low food intake.

Vitzthum's research challenges the past belief that nearly all early pregnancy losses are caused by genetic defects in the embryo. Genetic defects wouldn't change with the seasons, so Vitzthum's findings show that environmental factors must also play a major role in early pregnancy losses.

"This finding applies to U.S. moms just as much as Bolivians, and it applies to psychosocial resources just as much as food supply," Vitzthum said. "As well as healthy food, pregnant women also need good working conditions and adequate social support from family, friends and workplace to keep their risks of early pregnancy losses low."

Vitzthum's research is the first to show seasonality of early pregnancy loss in a non-industrialized population, and the first to demonstrate a relationship between economic activities and early pregnancy loss, she reported in the paper, "Seasonal Modulation of Reproductive Effort During Early Pregnancy in Humans," published in the American Journal of Human Biology.

In a second paper, "Seasonal and Circadian Variation in Salivary Testosterone in Rural Bolivian Men," Vitzthum reports a similar relationship between reproductive fitness and external influences like environmental conditions.

"This paper also concerns the effects of limited resources, this time on male physiology," she said. "In the worst part of the year, late winter, testosterone levels are suppressed. This is particularly interesting because it had been thought that males were much less sensitive, if at all, to environmental conditions because they don't need a lot of energy for a pregnancy. The effects of poor resources on males appear to be more subtle but can still be important for their own health and well being."

Vitzthum's work has long been at the crossroads of biology and culture, focusing on how human female reproductive functioning has evolved in response to different environmental conditions. "Until recently, it was assumed that women everywhere had similar reproductive biology. We now know that women vary tremendously, and these differences affect women's health."

"For example, high hormone levels increase the risk of breast cancer and other diseases. By studying the international patterns of hormone levels and how they relate to different environmental conditions," she said. "We hope to learn more about which women are at the greatest risks for these diseases." Doctors could then recommend extra monitoring or screening tests for those women, she added. In the mid-1990s while doing research at the Bolivian Institute for High Altitude Biology, Vitzthum found that Bolivian women, despite consuming about 25% less calories per day than the typical American woman eats, were able to conceive with lower hormone levels than were considered normal for American women. "This proved that the reproductive system has evolved to function adequately even in harsh conditions," she said. "Previously it had been thought that hormone levels this low would cause infertility."

Scientists have long wondered which parts of the diet influence hormone levels. To investigate this, Vitzthum is currently studying nomadic Mongolian herders, who have a total caloric intake similar to Bolivians, but a fat intake similar to Americans. Most recently Vitzthum spent a year at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, comparing hormone levels in women born in the former East and West Germany, where diet and activity patterns differed prior to reunification.

Vitzthum is presented an invited lecture, "Darwin's Legacy: An Evolutionary View of Reproduction." at the 2009 annual meeting of the International Academy of Sex Research in San Juan, Puerto Rico. She came to Indiana University in 2008 after earning a Ph.D. in Anthropology from the University of Michigan in 1986. "Understanding how human physiology has evolved to allow humans to reproduce in almost every environment has implications for the lives of families around the globe. Healthy families require adequate resources for parents and children. Evolutionary theory helps to explain the impact of living conditions on women's reproductive biology and health, and the trade-offs faced by all living organisms."

Reprinted from IU Discoveries, Indiana University, August, 2009.

Vitzthum, V. J., Thornburg, J., and Spielvogel, H. (2009). Seasonal Modulation of Reproductive Effort During Early Pregnancy in Humans. American Journal of Human Biology. DOI: 10.1002/ajhb.20936. Online version available at Wiley Interscience website.
Vitzthum, V. J., Worthman, C. M., Beall, C.M., Thornburg, J., Vargas, E., Villena, M., Soria, R., Caceres, E. and Spielvogel, H. (2009). Seasonal and Circadian Variation in Salivary Testosterone in Rural Bolivian Men. American Journal of Human Biology. DOI: 10.1002/ajhb.20927. Online version available at Wiley Interscience website.
Vitzthum, V.J. (2008). Evolutionary models of women’s reproductive functioning. Annual Review of Anthropology. 37: 53-73.



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