Introduction: Testosterone deficiency has a prevalence of 10-40% among adult males and 20% among adolescent and young adult (AYA) men (males 15-39 as per the National Cancer Institute). With increasing prevalence of low testosterone in general population, we hypothesized that serum total testosterone (TT) levels will decline in AYA men. The objective of this study was to analyze serum TT levels in AYA males using data from the National Health and Nutrition Examination Surveys (NHANES) 1999-2016. We hypothesized that serum TT levels in AYA men have decreased over time.
Methods: NHANES is a nationally representative cross-sectional survey that examines the US population and over samples targeted populations, to obtain adequate samples for subgroup analysis and more reliable variable estimates. We found data cycles which had values for serum TT and analyzed changes in serum TT over time controlling for year of study, age, race, body mass index (BMI), comorbidity status, alcohol and smoking use, and level of physical activity. During the study periods, three different assays (Biotin-Streptavidin from 1999-2004, IS-Liquid Chromatography from 2011-2012 and High-Performance-Liquid-Chromatography Tandem Mass Spectrometry from 2013 onwards) were used; they have shown comparable testosterone values with only some additional accuracy in the latest modality.
Results: A total of 4,045 men had TT measured from 1999-2016. After controlling for confounders, TT was lower among men in the later (2011-2016) versus earlier (1999-2000) cycles (all p < 0.001). Mean TT decreased over time: 605.39 ng/dL, 567.44, 424.96, 431.76 and 451.22 for 1999-2000, 2003-2004, 2011-2012, 2013-2014 and 2015-2016, respectively (p < 0.0001). Elevated BMI was associated with reduced TT levels (p < 0.0001) with mean BMI increasing from 25.83, 27.21, 27.12, 27.81, 27.96 for 1999-2000, 2003-2004, 2011-2012, 2013-2014 and 2015-2016, respectively, p = 0.0006. Even in men with normal BMI (18.5-24.9), TT levels have declined from 664.79 ng/dL to 529.24 ng/dL between 1999-2000 and 2015-2016 (p < 0.05).
Conclusions: This is the first study to report declining testosterone levels in adolescent and young adult men. Further studies are required to understand the etiology of low testosterone in AYA men. Source of