A-Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance--part 12

This part of our A–Z series contains five articles on a wide variety of topics. For the sake of continuity, some topics in the alphabetical listing have been moved further down: curcumin, which will appear collectively with flavonoids; docosahexanoic acid and eicosapentanoic acid, which will now come under the umbrella of fatty acids. The compounds covered in part 12 range considerably in their composition and their physiological roles in the body. However, they do share some common characteristics, which might be seen as a generic description of most of the supplements marketed to athletes. Each has a mechanism by which it is proposed that supplementation might improve sports performance, based on the enhancement of an existing biochemical or hormonal pathway that is considered limiting. The marketing credibility of each of these supplements, and others, is boosted from time to time by anecdotal reports of use by a successful athlete or popularity within a certain sporting population. For example, dehydroepiandrosterone achieved notoriety in sporting circles when American baseball player, Mark McGwire, provided testimonials regarding its use during the 1998 season in which he broke the league record for hitting home runs. Alternatively, dimethylglycine has enjoyed the mystique among Western athletes of being used by athletes from Eastern Bloc countries. However, the most important characteristic is that each product has received only minor attention from sports scientists, in terms of involvement in well-conducted, randomised, controlled trials, specific to sport. ### K Currell, A Syed Cysteine is a non-essential amino acid and, together with glycine and glutamate, is an important precursor of the tripeptide glutathione. Glycine and glutamate are readily available within the body and it is thought that the limiting step in the synthesis of glutathione is the availability of cysteine.1 Glutathione is one of the key antioxidants within the body2 and is an essential …