The immune system is highly reliant on accurate cell-cell communication for optimal function, and any damage to the signalling systems involved will result in an impaired immune responsiveness.
Oxidant-mediated tissue injury is a particular hazard to the immune system, since phagocytic cells produce
reactive oxygen species as part of the body's defence against
infection. Adequate amounts of neutralizing
antioxidants are required, therefore, to prevent damage to the immune cells themselves. Many
antioxidants can be obtained directly from the diet (e.g.
ascorbic acid,
alpha-tocopherol,
carotenoids and polyphenolic
flavonoids) or require
micronutrients as integral components (e.g. Se in the metalloenzyme
glutathione peroxidase (EC 1.11.1.9)). Numerous epidemiological studies have found strong associations between diets rich in
antioxidant nutrients and a reduced incidence of
cancer, and it has been suggested that a boost to the body's immune system by
antioxidants might, at least in part, account for this. Although more striking effects have been observed in the elderly, there is also evidence that
antioxidant nutrients can modify cell-mediated immune responses in younger individuals. Indeed, it might be essential to have an adequate intake of
antioxidant nutrients from an early age in order to help prevent the development of, or at least delay the onset of, several degenerative disorders. The present paper will review the effects of specific nutrients on immune function in young to middle-aged human subjects, focusing on the
antioxidant vitamins C and E, and on Se. A further review, dealing more specifically with the effects of
carotenoids on human immune function, will be presented at a forthcoming meeting of the Nutrition Society.