ORIGINAL RESEARCH Three Weeks of Creatine Monohydrate Supplementation Affects Dihydrotestosterone to Testosterone Ratio in College-Aged Rugby

Objective: This study investigated resting concentrations of selected androgens after 3 weeks of creatine supplementation in male rugby players. It was hypothesized that the ratio of dihydrotestosterone (DHT, a biologically more active androgen) to testosterone (T) would change with creatine supplementation. Design: Double-blind placebo-controlled crossover study with a 6-week washout period. Setting: Rugby Institute in South Africa. Participants: College-aged rugby players (n = 20) volunteered for the study, which took place during the competitive season. Interventions: Subjects loaded with creatine (25 g/day creatine with 25 g/day glucose) or placebo (50 g/day glucose) for 7 days followed by 14 days of maintenance (5 g/day creatine with 25 g/day glucose or 30 g/day glucose placebo). Main Outcome Measures: Serum T and DHTwere measured and ratio calculated at baseline and after 7 days and 21 days of creatine supplementation (or placebo). Body composition measurements were taken at each time point. Results: After 7 days of creatine loading, or a further 14 days of creatine maintenance dose, serum T levels did not change. However, levels of DHT increased by 56 % after 7 days of creatine loading and remained 40 % above baseline after 14 days maintenance (P, 0.001). The ratio of DHT:T also increased by 36 % after 7 days creatine supplementation and remained elevated by 22 % after the maintenance dose (P, 0.01). Conclusions: Creatine supplementation may, in part, act through an increased rate of conversion of T to DHT. Further investigation is warranted as a result of the high frequency of individuals using creatine supplementation and the long-term safety of alterations in circulating androgen composition. Statement of Clinical Relevance: Although creatine is a widely used ergogenic aid, the mechanisms of action are incompletely understood, particularly in relation to dihydrotestosterone, and therefore the long-term clinical safety cannot be guaranteed. Key Words: creatine supplementation, rugby player, athlete, clinical safety, DHT:T rati