The association between physiologic testosterone levels, lean mass, and fat mass in a nationally representative sample of men in the United States.

Testosterone deficiency leads to increased muscle loss with aging and increased fat mass. Supraphysiologic levels cause an increase in muscle mass and decrease in fat mass. The difference in lean and fat mass across physiologic levels of testosterone has been under examined in men. OBJECTIVE Examine the association between physiologic testosterone levels with lean and fat mass. METHODS Data from the 1999-2000 NHANES were used (n=252 men; 18-85yrs). Testosterone and SHBG values were obtained by a morning blood sample. Body composition was measured by DXA. Multivariable linear regression was used to compute unadjusted, minimally adjusted, and extended models of relative upper- and lower-body lean and fat mass. RESULTS In the extended model, men with total testosterone levels in the highest 25% (4th quartile) had more lower-body lean mass (LBLM) (β=22.1(%), 95%CI: 9.0, 35.3, p=0.003) and upper-body lean mass (UBLM) (β=5.6(%), 95%CI: 0.1, 11.2, p=0.046), and less lower-body fat mass (LBFM) (β=-9.9(%), 95%CI: -17.7, -2.1, p=0.016) and upper-body fat mass (UBFM) (β=-6.1(%), 95%CI: -10.1, -2.1, p=0.005) than those in the 1st quartile. Men in the 3rd quartile had more LBLM (β=14.2, 95%CI: 5.3, 23.1, p=0.004), UBLM (β=5.6, 95%CI: 2.0, 9.2, p=0.004), and less LBFM (β=-9.7(%), 95%CI: -16.7, -2.7, p=0.010) and UBFM (β=-4.7(%), 95%CI: -8.3, -1.2, p=0.012) than those in the 1st quartile. CONCLUSION These findings suggest that, at physiologic levels, an association exists between higher levels of testosterone and favorable lean and fat measures.