Population variation in age-related decline in male salivary testosterone.

BACKGROUND Age-related declines in free and bioavailable testosterone are frequently reported for Western populations, but interpopulation variation in this pattern has not previously been investigated. METHODS Salivary testosterone was measured using a consistently applied protocol on morning samples collected from men in four populations (USA, Congo, Nepal, and Paraguay) representing different geographical, ecological, and cultural settings. RESULTS Mean testosterone levels varied significantly between the four populations. The mean testosterone differences between populations were greatest for young men (aged 15-30 years) and insignificant for older men (aged 45-60 years). The slope of age-related decline in testosterone was significant in the USA and Congolese participants, but not in the Nepalese or Paraguayan participants. CONCLUSIONS Age patterns of testosterone decline vary between populations primarily as a result of variation in the peak levels attained in young adulthood. The potential consequences of this variation for other aspects of male health deserve investigation.