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This week we review the evidence on whether creatine has a role as a sports supplement. We would be very pleased if you were to share this publication with health professional friends and colleagues.

Study 1: Creatine and muscle strength


Creatine supplementation when combined with resistance training improves strength in young men, according to a new meta-analysis of controlled trials.

Subjects/method: A meta-analysis combining data from 16 studies published between 1996 and 2000. These trials involved 20 discrete samples totalling 414 subjects, most of whom were young men.

Results: There was a significant improvement in strength on creatine supplementation - see Table 1. (Although increase in arm flexor strength is shown as being not statistically significant, it was modestly significant in the only trial whichi did not involve subjects over 60 years of age).

Reference: J Fam Pract. 2002 Nov;51(11):945-51.


Study 2: Creatine supplementation sub-analysis

A different meta-analysis was able to narrow down the effects of creatine supplementation on body composition, performance and in relation to the way that the supplement was given.

Subjects/method: Meta-analysis of 100 randomised, placebo-controlled, double-blinded trials (RCTs).

Results: There were small but statistically significant improvements in body composition (especially lean body mass), exercise duration and intensity.

The effect was greater following short-term supplementation, for repetitive and laboratory-based rather than `in the field' exercise (and for upper body resistance exercise of short duration (e.g. isometric, isokinetic, and isotonic).

Reference: Int J Sport Nutr Exerc Metab. 2003 Jun;13(2):198-226.



COMMENTS

Several months ago (in issue #166) we concluded that certain amino acids supplements might be useful in building muscle mass in the elderly, provided resistance exercise was also undertaken.

One such amino acid is creatine, found in meat and fish (as well as being synthesised from other amino acids). Creatine is also relevant in sports nutrition.

This is because muscles undertaking maximal exertion of short duration (<30 seconds) require energy derived from ATP regenerated by the anaerobic metabolism of phosphocreatine (along with glycogen) (ref.1). Indeed, there is evidence that fatigue in such exercise is related more to low phosphocreatine than high lactate levels (refs.2).

This applies particularly to sports requiring single or repeated short duration bursts of muscle activity, such as power lifting or the short sprints characteristic of football. Creatine supplementation has already become popular amongst such athletes. Happily, the science in this case is also quite encouraging.

Quite a lot of research on creatine supplementation in sports medicine has been published over the last ten years. Whilst not all trials agree, overall there seems little doubt that creatine supplements can reduce fatigue and enhance performance during short duration, high intensity exercise, both one-off and or intermittent. It also seems to increase lean body mass when used in conjunction with resistance exercise.

The new meta-analyses include many of the clinical trials that support these conclusions. And there are more of them. These two meta-analyses included trials published up to the year 2000. The editorial team here at Arbor has identified a further 27 clinical trials published since that time, 21 of which had positive results.

The reason why creatine increases body weight is probably because of water retention initially. But in the presence of resistance training `swollen muscle' is likely to result in real growth in lean muscle mass (refs.1, 3).

The meta-analysis in Study 2 contributes to our growing understanding of the best way to take creatine supplements. Doses of around 15-30 gms/day (~20x typical dietary intake) over 4-6 days prior to exercise seem to offer the best results. Higher or longer term maintenance dosage is not likely to add to the impact (refs.1, 3, 4).

Two other ways have been suggested to maximise effectiveness: to combine creatine supplements with exercise (to increase muscle utilisation) and to consume it with carbohydrate (to raise absorption) (ref.1).

The impact is also greater when initial creatine levels are low (ref.1). For example, a recent study found these supplements increased lean mass and muscle strength more in vegetarians than non-vegetarians (who had higher initial muscle creatine levels) (ref.5).

Regarding safety, the most prudent conclusion is that we do not yet know enough to be sure about safety over long term administration or at very high doses. Evidence so far has been reassuring, and does not confirm anecdotal reports of minor side-effects (refs.1, 3, 5-9), nor theoretical concerns that excess creatine (which is excreted as creatinine) might impair renal function (refs.10)

References:

  1. Am J Clin Nutr. 2000 Aug;72(2 Suppl):607S-17S.
  2. J Appl Physiol 1986;60:1839-42.
  3. Clin Pharmacokinet. 2003;42(6):557-74.
  4. Can J Appl Physiol. 2002 Dec;27(6):663-81.
  5. Med Sci Sports Exerc. 2003 Nov;35(11):1946-1955.
  6. Sports Med. 2000 Sep;30(3):155-70.
  7. J Strength Cond Res. 2003 Feb;17(1):26-33.
  8. Mol Cell Biochem. 2003 Feb;244(1-2):83-8.
  9. Mol Cell Biochem. 2003 Feb;244(1-2):95-104.
  10. Br J Sports Med. 2000 Aug;34(4):284-8.

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