Serum testosterone and urinary steroid profiles after administration of a zinc supplement

The nutritional supplement ZMA® is labelled to contain zinc (as monomethionine and aspartate; 30 mg per recommended dose), magnesium (450 mg as aspartate), and vitamin B6 (10.5 mg). According to a supplementation trial by Brilla and Conte, the use of ZMA® by semi-professional athletes resulted in an increase of plasma testosterone (T) levels of ca. 30 % and significantly improved muscle strength when compared to athletes taking placebo. These results have to be considered very carefully for two reasons: One of the authors, Victor Conte, has been the major player in the BALCO case and was convicted for distributing performance enhancing drugs (e.g. THG, hGH, EPO). Numerous studies have demonstrated that nutritional supplements may contain so called prohormones and also synthetic steroids, which are not declared on the label. Except for this trial, zinc supplementation has only been reported to increase testosterone in cases of zinc deficiency and in elderly patients. The present trial could not confirm the results of the previous study conducted by Brilla and Conte, who reported an increase of plasma testosterone levels after use of ZMA®. Even though the supplementation of ZMA® raised serum and urine zinc and therefore contributed to the zinc nutriture of the subjects, it had no effects on serum and urine markers of testosterone and its metabolism. This is most likely due to the sufficient dietary zinc intake of the participants of the trial. Prolonged use of ZMA® might have adverse effects: The upper limit of 40 mg zinc-day-1, which is considered to be safe, is exceeded by use of ZMA® (30 mg*day-1) additionally to a normal diet (approximately 15*mg-day-1). Anaemia, impaired immune functions, and changes of lipoprotein levels have been reported after a prolonged zinc intake beyond 40 mg*day-1. So, athletes are unlikely to benefit from use of ZMA® with respect to their anabolic hormone profile but may face negative side effects due to the high zinc content of the supplement. Aus dem Text (geändert)