Seasonal and circadian variation in salivary testosterone in rural Bolivian men

• Type of Material: Article
• Authors: Virginia J. Vitzthum, Indiana University; Carol Worthman, Emory University; Cynthia M. Beall, Case Western Reserve University; Jonathan Thornburg, Indiana University; Enrique Vargas, Instituto Boliviano de Biología de Altura; Mercedes Villena, Instituto Boliviano de Biología de Altura; Rudy Soria, Instituto Boliviano de Biología de Altura; Esperanza Caceres, Instituto Boliviano de Biología de Altura; Hilde Spielvogel, Instituto Boliviano de Biología de Altura
• Language: English
• Date: 2009-11
• Publisher: Wile
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © 2009 Wiley-Liss, Inc.
• Final Published Version (URL): http://dx.doi.org/10.1002/ajhb.20927
• Title of Journal or Parent Work: American Journal of Human Biology
• ISSN: 1042-0533
• Volume: 21
• Issue: 6
• Start Page: 762
• End Page: 768
• Grant/Funding Information: This work was supported by grants from the U.S. National Science Foundation (SBR 9221724 to CMB, SBR 9506107 to VJV), the U.S. National Institutes of Mental Health (MH57761 to CMW), and the University of California Regents (to VJV).
• Keywords: Bolivia; aging; testosterone; seasonality; circadian rhythms; andrology
• Research Categories: Biology, General; Anthropology, Physical; Anthropology, Medical and Forensic

Abstract

Testosterone (T) plays a key role in the increase and maintenance of muscle mass and bone density in adult men. Life history theory predicts that environmental stress may prompt a reallocation of such investments to those functions critical to survival. We tested this hypothesis in two studies of rural Bolivian adult men by comparing free T levels and circadian rhythms during late winter, which is especially severe, to those in less arduous seasons. For each pair of salivary TAM/TPM samples (collected in a ~12-hour period), circadian rhythm was considered classic (CCLASSIC) if TAM>110%TPM, reverse (CREVERSE) if TPM>110%TAM, and flat (CFLAT) otherwise. We tested the hypotheses that mean TAM>mean TPM and that mean TLW<mean TOTHER (LW=late winter, OTHER=other seasons). In Study A, of 115 TPM-TAM pairs, 51%=CCLASSIC, 39%=CREVERSE, 10%=CFLAT; in Study B, of 184 TAM-TPM pairs, 55%=CCLASSIC, 33%=CREVERSE, 12%=CFLAT. Based on fitting linear mixed models, in both studies TOTHER-AM>TOTHER-PM (A: p=0.035, B: p=0.0005) and TOTHER-AM>TLW-AM (A: p=0.054, B: p=0.007); TPM did not vary seasonally, and T diurnality was not significant during late winter. T diurnality varied substantially between days within an individual, between individuals and between seasons, but neither T levels nor diurnality varied with age. These patterns may reflect the seasonally varying but unscheduled, life-long, strenuous physical labor that typifies many non-industrialized economies. These results also suggest that single morning samples may substantially underestimate peak circulating T for an individual and, most importantly, that exogenous signals may moderate diurnality and the trajectory of age-related change in the male gonadal axis.