A population-level decline in serum testosterone levels in American men.
Level 3 - non-randomized controlled study
Prospective cohort study with repeated measures over time
PubMed 17062768 · doi:10.1210/jc.2006-1375
What was done
Researchers evaluated data from a prospective cohort study of randomly selected men aged 45–79 years residing in greater Boston, Massachusetts. Serum total testosterone and calculated bioavailable testosterone were measured across three examination waves: baseline (T1: 1987–1989 [reported in abstract as 1987–1999]), wave 2 (T2: 1995–1997), and wave 3 (T3: 2002–2004). The analysis assessed whether calendar-time population-level changes occurred independent of chronological aging and whether they could be explained by changes in relative weight, smoking, or other health and lifestyle factors.
What was found
The analysis included 2,769 total observations from 1,532 men (1,374 at T1; 906 at T2; 489 at T3). The authors observed a substantial age-independent decline in testosterone over time that was larger in magnitude than cross-sectional declines typically associated with aging. This decline was not attributable to observed changes in explanatory factors such as obesity or smoking. The abstract provides no specific numerical values, percentages, or effect sizes.
Why it matters
This study provides longitudinal evidence that male testosterone concentrations decreased across calendar time and birth cohorts independent of aging, suggesting that unrecognized environmental or population-level health factors drive broader endocrine changes.
Limits
The abstract reports no numerical estimates, effect sizes, or confidence intervals. The study population was restricted to a single geographic area (greater Boston), limiting generalizability. There was substantial loss to follow-up over the study waves (from 1,374 men at T1 to 489 at T3), introducing potential attrition bias, and unmeasured environmental or behavioral confounders were not accounted for.
Cited by
- supports Average testosterone levels in men have decreased by up to 20% over the last two decades.