Adiposity, not chronological aging, is the dominant determinant of circulating testosterone in US adult men.

CONTEXT: Age-related decline in serum testosterone is commonly cited as justification for testosterone replacement therapy, yet adiposity may represent a major modifiable determinant of circulating testosterone. OBJECTIVE: To quantify the relative contributions of age, total adiposity, and visceral adiposity to circulating testosterone concentrations and prevalence of biochemical low testosterone in US adult men. DESIGN: Cross-sectional nationally representative analysis. SETTING: National Health and Nutrition Examination Survey (NHANES) 2011-2016. PARTICIPANTS: Men aged 20 to 59 years with valid serum testosterone measurements (n = 4984). MAIN OUTCOME MEASURES: Total testosterone (ng/dL) and the prevalence of biochemical low testosterone (testosterone <300 ng/dL). RESULTS: Age explained only 2.5% of the variation in circulating testosterone (pseudo-R 2 = 0.025). In contrast, dual-energy X-ray absorptiometry (DXA)-derived total percent body fat and visceral adipose tissue (VAT), and waist circumference each explained ∼18% to 20% of testosterone variability. Waist circumference demonstrated slightly greater explanatory performance than DXA-derived VAT, indicating that simple anthropometric assessment captures much of the clinically relevant information provided by advanced imaging. Similar inverse associations were observed using multiple biochemical testosterone thresholds (300, 250, 200, and 150 ng/dL). Biochemically low testosterone was consistently associated with substantially greater adiposity across all age groups. CONCLUSION: Measures of adiposity consistently demonstrated substantially stronger associations with circulating testosterone than chronological age alone. Waist circumference performed comparably to DXA-derived VAT, supporting its use as a clinically accessible marker of obesity-related testosterone suppression.