24-HOUR MEAN PLASMA TESTOSTERONE CONCENTRATION DECLINES WITH AGE IN NORMAL PREMENOPAUSAL WOMEN

The 24-h mean plasma concentration of total testosterone (T) was measu red in 33 healthy, regularly cycling, nonobese women between 21 and 51 yr of age. Percent free T was measured in 17 of them. Plasma dehydroe piandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS) were measured in 24 of them, and the DHEA-to-T and DHEAS-to-T ratios were c alculated. It was found that the concentration of total T showed a ste ep decline with age; the regression equation was: T (nanomoles per L) = 37.8 x age(-1.12)(r = -0.54; P < 0.003). According to this equation, the expected T concentration of a woman of 40 would be 0.61 nmol/L, a bout half that of a woman of 21 (1.3 nmol/L). The percent free T did n ot vary significantly with age, so free T concentration likewise showe d a steep decline with age. The DHEA-to-T and DHEAS-to-T ratios were b oth age invariant, clearly because the levels of DHEA and DHEAS also d ecline steeply with age, as previously reported.