Decline in Serum Testosterone Levels Among Adolescent and Young Adult Men in the USA.

Testosterone deficiency has a prevalence of 20% among adolescent and young adult (AYA) males. Although previous studies have shown that total testosterone (TT) levels are declining in the population compared to prior decades, no study has identified TT level trends for AYA males specifically. Using data from the National Health and Nutrition Examination Surveys, we investigated TT levels for 4045 men from 1999 to 2016. After controlling for confounders, we found that mean TT levels declined over time: TT levels were lower in the later (2011-2016) than in the earlier (1999-2000) cycles (all p < 0.001). Elevated body mass index (BMI) was associated with lower TT, but the trend remained significant even among men with normal BMI. Limitations include the influence of confounding variables such as environmental factors and the use of differing assays for TT measurement. Further studies using other data streams are needed to validate these findings. PATIENT SUMMARY: In this report we looked at data for adolescent and young adult men in a US national database on total testosterone (TT) levels. There has been a decline in mean TT levels over the past two decades and TT is lower with progressively higher body mass index. We conclude that TT levels have been declining in young adult men in recent decades.