Christopher W. Kuzawa, Alexander V. Georgiev, Thomas W. McDade, Sonny Agustin Bechayda, Lee T. Gettler
Circulating testosterone (T) follows a diurnal pattern with high waking levels that decline across the day. The hypothalamic-pituitary-adrenal axis produces cortisol in a similar manner but also undergoes an abrupt increase in hormone secretion immediately upon waking (a cortisol awakening response, CAR). Whether the hypothalamic-pituitary-gonadal axis, and circulating T levels, exhibit a similar post-waking response is unclear. Here we describe post-waking T changes in a sample of 108 young adult males from metropolitan Cebu City, the Philippines. As expected, salivary T was higher at waking than in the evening but, remarkably, 60 % of this diurnal decline occurred within 30 min of awakening. There was a strong inverse linear relationship between waking T and the post-waking T decline, such that men with higher waking T experienced a more rapid decline in the hormone. Even though fathers had lower waking T, they experienced a greater post-waking decline than non-fathers. Men with a larger positive CAR had modestly attenuated post-waking T declines. We speculate that these findings reflect a testosterone awakening response (TAR) that helps partition the target tissue effects of T by time of day. T rises overnight to facilitate muscle anabolism at a time when the hormone’s impacts on social behavior are limited. Upon waking, the rapid drop in T helps shift from anabolic to catabolic processes in support of physical activity, while also calibrating T levels in line with the competing social priorities of the individual, as determined by the current balance of behavioral investment towards mating and parental effort. © 2015, Springer International Publishing.
Department of Anthropology, Northwestern University, 1810 Hinman Avenue, Evanston, 60208, IL, United States; Institute for Policy Research, Northwestern University, Evanston, 60208, IL, United States; Office of Population Studies Foundation, University of San Carlos, Cebu, Philippines; Department of Sociology, Anthropology and History, University of San Carlos, Cebu City, Philippines; Department of Anthropology, Notre Dame University, South Bend, 46556, IN, United States
