Safety of long-term creatine supplementation in women's football players: a real-world in-season study

Although creatine supplementation is well established for enhancing athletic performance, data on its long-term safety are still limited, particularly among female athletes. This study investigated the effects of in-season creatine supplementation on biochemical safety markers in young female football players. This real-world, longitudinal single-arm study assessed the safety of creatine supplementation during a competitive season in 71 female athletes from youth and professional football teams. Participants received 20 g/day of creatine monohydrate for 7 days, followed by 5 g/day for the remainder of the season. Dietary intake and a comprehensive panel of hematological, renal, and hepatic biomarkers were evaluated at baseline, mid- (week 16), and end-season (week 32). Linear mixed-model with repeated measures analysis revealed that 8 out of 18 biochemical markers showed statistically significant though clinically minor fluctuations throughout the season. All analytes, except creatine phosphokinase (CPK), remained within reference ranges. No adverse effects were observed on renal (e.g. glomerular filtration rate, creatinine, urea, albuminuria) or hepatic (ALT, AST) function. CPK levels variation likely reflected training load rather than supplementation effects. In this single-arm in-season cohort, long term creatine supplementation was not associated with clinically meaningful derangements in biochemical safety markers in female football players. These findings support the long-term safety profile of creatine in this population and encourage further research into its sex-specific effects in athletic settings.