Data from 71 female athletes from youth and professional football teams showed that while daily creatine consumption did produce some minor fluctuations in safety biomarkers, these were all within clinical reference values.
“Although minor fluctuations in blood biochemical safety markers were observed throughout the season, all biomarkers remained within clinical reference values during long-term creatine supplementation,” wrote scientists from the University of São Paulo and Sport Club Corinthians Paulista in the Journal of the International Society of Sports Nutrition. “These results suggest that creatine supplementation is safe and well tolerated in female football players over the course of an entire competitive season.
“Our findings add to a large body of evidence supporting the safety of creatine across a broad range of individuals, from clinical populations to athletes.”
Impressive
Commenting independently on the new study, Susan Kleiner, PhD, RD, owner and founder of High Performance Nutrition LLC, told NutraIngredients that she was very impressed with the design and methodology of the study, as well as the reliability and validity of the data.
“These young women were studied within the methodical confines of female biology,” Dr. Kleiner said.
“There was 100% participation, and we saw no abnormalities in about every measure you could look at over eight months. There were some changes halfway through the study, but they were transient and went back to baseline by the end.”
She noted that the dietary data from the younger subjects also showed that the women were under-fueling and provides further confirmation that female athletes do not eat enough.
“Now, can we do a study in older women, especially if we’re telling older women to take more creatine for the bone and brain benefits?” Dr. Kleiner added. “We do need studies for women as they age. However, despite the lack of long-term data on older women, I’m confident that creatine supplementation is safe.”
Study details
The researchers recruited 71 female soccer players from youth (under 17s and under 20s) and professional football (soccer) teams to participate in their real-world, longitudinal single-arm study. The players all received 20 grams of creatine per day during an initial seven day loading phase and then 5 grams per day for the rest of the season.
Data from a comprehensive hematological, renal and hepatic panel revealed that eight out 18 biochemical markers showed statistically significant changes throughout the season, although these were described as “clinically minor”. All remained within reference ranges with the exception of creatine phosphokinase (CPK).
“CPK levels variation likely reflected training load rather than supplementation effects,” the researchers wrote.
No adverse effects were observed on kidney (e.g. glomerular filtration rate, creatinine, urea, albuminuria) or liver (ALT, AST) function, they added.
“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,” the study concluded. “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.”
Source: Journal of the International Society of Sports Nutrition, 22(sup1). doi: 10.1080/15502783.2025.2591782. “Safety of long-term creatine supplementation in women’s football players: a real-world in-season study”. Authors: M.P. Garcia, et al.
