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09.11.2010


NAC helps some athletes to speed up

Large quantities of the amino acid N-acetylcysteine [NAC, structural formula shown below] extend the length of time you can do intensive physical exercise. For some athletes, at least. For others, the amino acid has no effect at all, according to sport scientists at the University of Exeter in England.

N-Acetylcysteine is sold as a supplement and as a medicine. Supplements manufacturers usually sell it as an antioxidant. It is a precursor of glutathione, a small protein that detoxifying enzyme use to neutralise harmful compounds. Manufacturers of cough medicines like Bisolvon claim that N-acetylcysteine helps loosen phlegm.


Recent studies suggest that N-acetylcysteine raises the amount of nitrogen monoxide in the bloodstream. The amino acid neutralises free radicals, thus preventing them from deactivating the enzymes that produce NO. More NO boosts the muscle cellsí oxygen uptake, and therefore also boosts endurance performance. Thatís the theory at least. The researchers wanted to know if this is what actually happens in practice.

Eight male amateur athletes were given an intravenous solution of 2.5 g N-acetylcysteine for 15 minutes. After that they had to cycle, following a protocol that tested how long they could keep up for at 80 percent of their VO2max. During the test, which lasted an hour and a quarter, the subjects were fed another 2 g N-acetylcysteine intravenously. This was enough to maintain the level of free sulphhydryl groups Ė i.e. N-acetylcysteine [see below].





The figure above shows how long the test subjects managed to keep up intensive exertion, compared with the their times when they were given a placebo [PLA]. For the group as a whole, the amino acid did not have a statistically significant effect: it extended the time by 13 percent.

But when the researchers looked at each case individually, they noticed that almost in almost half of the subjects the N-acetylcysteine reduced the time by 4-14 percent, and in the other half it increased the time by 24-69 percent. So most athletes stand to gain nothing from N-acetylcysteine, but there are a few for whom the amino acid works just as well as the illegal stuff.

The researchers have not yet worked out the mechanism behind the effect of N-acetylcysteine. But they did manage to work out that the amino acid has no effect on NO or on oxygen uptake.

Two years ago Iranian researchers announced that a combination of N-acetylcysteine and selenium raises testosterone levels.

Source:
Respir Physiol Neurobiol. 2010 Oct 15. [Epub ahead of print].

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