Despite the extensive use of creatine monohydrate for performance enhancement, few studies have examined the potential side effects of supplementation and none has directly compared the response to supplementation in men and women.

This gap in knowledge has now been filled by a Canadian study of young, healthy, physically active men and women, which showed no adverse effects of short-term treatment but greater body-building benefits for men than for women.

Fifteen men and 15 women were randomly assigned to five days' supplementation with 20g per day of either creatine monohydrate (CrM) or a similar-looking inactive substance (placebo) after extensive pre-trial checks, including measurement of body composition, blood pressure and maximal strength. On day six they returned to the lab for retesting. Blood pressure was unaffected by supplementation, and blood tests suggested there were no effects on kidney function. Plasma levels of the muscle enzyme creatine kinase, which is thought to have potentially damaging effects at increased levels, was unaffected by treatment.

As far as body composition was concerned, there was no effect of treatment on percentage body fat but clear increases in both total body mass (TBM) and fat-free mass (FFM). However, these changes were much smaller for women than for men: men increased both TBM and FFM by 2%, while for women the respective increases were only 0.8 and 1.0%. CrM treatment had no effect on grip strength during forearm tests and no significant effect on resting and post-exercise blood lactate levels. The implication of these findings is that creatine monohydrate may be less useful as a performance-enhancing aid for women than for men. 'It was not anticipated a priori that such large sex differences would exist in response to CrM loading, given that the subjects were matched for age and training status,' explain the researchers. They point out that it is possible the women had higher muscle concentrations of total creatine before supplementation, which might have reduced its effectiveness.

In terms of safety CrM gets the thumbs-up, although the potential side effects of long-term supplementation have yet to be examined. In addition to its benefits for athletes, CrM could also be used to treat people with muscle atrophy and other wasting conditions.

Med Sci Sports Exerc 2000 Feb 32 (2) 291-6

Isabel Walker