Serum testosterone and urinary excretion of steroid hormone metabolites after administration of a high-dose zinc supplement

Abstract

Objectives: To investigate whether the administration of the zinc-containing nutritional supplement ZMA causes an increase of serum testosterone levels, which is an often claimed effect in advertising for such products; to monitor the urinary excretion of testosterone and selected steroid hormone metabolites to detect potential changes in the excretion patterns of ZMA users. Subjects: Fourteen healthy, regularly exercising men aged 22-33 years with a baseline zinc intake between 11.9 and 23.2 mg day-1 prior to the study. Results: Supplementation of ZMA significantly increased serum zinc (P = 0.031) and urinary zinc excretion (P = 0.035). Urinary pH (P = 0.011) and urine flow (P = 0.045) were also elevated in the subjects using ZMA. No significant changes in serum total and serum free testosterone were observed in response to ZMA use. Also, the urinary excretion pattern of testosterone metabolites was not significantly altered in ZMA users. Conclusions: The present data suggest that the use of ZMA has no significant effects regarding serum testosterone levels and the metabolism of testosterone in subjects who consume a zinc-sufficient diet.