Cross-sectional association between physical activity and serum testosterone levels in US men: results from NHANES 1999-2004.

Testosterone levels and physical activity each play important roles in men's health, but the relationship between the two remains unclear. We evaluated the cross-sectional association between self-reported total physical activity and serum testosterone levels in 738 men (mean age 42.4 years, range 20-≥85 years) who participated in National Health and Nutrition Examination Survey 1999-2004. We compared geometric mean testosterone concentrations measured by radioimmunoassay (RIA) and calculated the odds ratio (OR) of having low or low normal testosterone (≤3.46 ng/mL) across tertiles of total physical activity in all men, and men stratified by age (20-49, ≥50 years), and obesity status (BMI < 30, ≥30 kg/m(2) ). The geometric mean testosterone concentration was 5.31 ng/mL; 18.6% of the men had low or low normal serum testosterone levels. Physical activity tertiles were not associated with testosterone levels overall, or when stratified by age or obesity status. Similarly, there was no association between physical activity tertiles and the odds of low or low normal testosterone, overall or by age. However, among non-obese men, those in the highest physical activity tertile were significantly less likely to have low or low normal testosterone than those in the lowest tertile (OR 0.50; 95% CI = 0.26-0.95); there was no association among obese men. Greater physical activity was not associated with testosterone levels, but may be associated with a reduced odds of low or low normal testosterone in non-obese men, but not in obese men.