Glutathione is a tripeptide synthesised from cysteine, glutamic acid and glycine. Glutathione is the primary water soluble antioxidant in both animal and plant tissues and in this role it protects cells from damage by oxidative stress. Glutathione can function as an effective water soluble antioxidant because of the presence of a sulphur group in its structure. This sulphur can donate a hydrogen to reduce other compounds, and in doing so becomes oxidised itself. Studies show that glutathione levels are associated with health and so chronic oxidative stress than can deplete cellular levels of glutathione may be the underlying cause of many diseases of Western origin. Physical exercise is also able to deplete cellular stores of glutathione. Generally if enough rest is provided between training sessions glutathione stores recover and may even improve through supercompensation. However, chronic overtraining that provides inadequate recovery periods may cause long term depletion of glutathione stores and this may explain the disease associated with the stress of exhaustive physical activity.
Antioxidants in the diet may be able to boost cellular levels of glutathione. This relates to the way antioxidants interact. Dietary intakes of vitamin C for example have been shown to spare cellular glutathione and thus increase tissue levels of glutathione. Another way to increase cellular levels of glutathione is to increase dietary intakes of the amino acid cysteine. Cysteine is the rate limiting amino acid for glutathione synthesis and so poor glutathione status in combination with inadequate cysteine in the diet retards the synthesis of glutathione and cellular levels drop. During periods of chronic oxidative stress, cysteine may become conditionally essential due to its role in the synthesis of glutathione. One way to increase dietary intakes of cysteine is by taking the supplement N-acetyl-L-Cysteine (NAC). Supplements of NAC have been shown to be effective at promoting glutathione synthesis. Another way to boost cellular glutathione is to increase intakes of dietary proteins that are high in cysteine. Whey protein is particularly high in cysteine and thus may replete cellular levels of glutathione.