Decline in Serum Testosterone Levels Among Adolescent and Young Adult Men in the USA.
Level 4 - case-series / case-control
Repeated cross-sectional analysis of national survey data
PubMed 32081788 · doi:10.1016/j.euf.2020.02.006
What was done
Researchers analyzed total testosterone (TT) levels in 4,045 adolescent and young adult men using cross-sectional data from the US National Health and Nutrition Examination Surveys (NHANES) collected between 1999 and 2016, controlling for potential confounding factors.
What was found
Mean total testosterone levels significantly decreased over time, with lower levels observed in 2011–2016 compared to the 1999–2000 cycles (all p < 0.001). While higher body mass index (BMI) correlated with lower total testosterone, the downward trend across survey cycles remained statistically significant among men with normal BMI. Specific numerical testosterone values or effect sizes were not reported in the abstract.
Why it matters
This study demonstrates that the secular decline in male testosterone levels observed in older cohorts also affects adolescent and young adult men, and that rising obesity rates do not fully explain the trend.
Limits
The study relied on repeated cross-sectional surveys rather than longitudinal tracking of individuals. The abstract notes that differing laboratory assays were used for testosterone measurement over time and that unmeasured confounding factors, such as environmental exposures, could not be fully controlled.
Cited by
- supports Average male testosterone levels declined by approximately 25% between the late 1990s (around 600 ng/dL) and 2015 (around 450 ng/dL).