Decline in testosterone levels seen among American men

A substantial, yet unrecognized age-dependent population-level decrease in testosterone in American men has been observed, potentially due to birth cohort differences or to health or environmental effects not captured in observed data, suggest researchers from the New England Research Institutes, Watertown, MA.

The researchers conducted a prospective cohort study of health and endocrine functioning in randomly selected men ages 45 to 70 years. They collected data at three time points ( T1: 1987-1989; T2: 1995-1997; T3: 2002-2004). Data were obtained on 1,374, 906, and 489 men at T1, T2, and T3, respectively, totaling 2,769 observations taken on 1,532 men.

The researchers observed a substantial age-dependent decline in testosterone that does not appear to be attributable to observed changes in explanatory factors, including health and lifestyle characteristics such as smoking and obesity, they said. The estimated population-level declines are greater in magnitude than are the cross-sectional declines in testosterone typically associated with age.