Vitamin E and the immune response

Undernourishment has been suggested to be the most frequent cause of secondary immunodeficiency in man (Chandra et al. 1978) and a practical consequence of this is that nutritional deficiency leads to a significantly increased susceptibility to infection. The association of immune deficiency and protein-energy malnutrition is well described and reviewed (Dowd & Heatley, 1984) and there is now increasing awareness as well as published evidence, that individual nutrients may have a major influence on immune function. The number of individual micronutrients reported to have an influence on immune function is ever increasing and includes the elements, zinc, copper, iron, selenium and magnesium, as well as the vitamins, folic acid, B12, C, B6, A, p-carotene and E. Several of these individual micronutrients will be considered in the present symposium and this communication will examine the evidence in relation to vitamin E. Since single nutrient deficiency is uncommon in human populations, the majority of studies reported in relation to vitamin E and indeed other micronutrients, have been performed in experimental animals. One is then immediately faced with the unanswered problem of extrapolating results in animals to humans and since many of the studies in animals have looked at the extremes of nutritional state, either gross depletion or supplementation at levels greatly in excess of recommended intakes, extrapolation becomes even more difficult. Added to these difficulties, the complexity of the immune system, involving processes such as mucosal and cell-mediated immunity, complement function, phagocytosis and intracellular killing, further complicates interpretation of results. Very few studies have been performed on the effect of vitamin E on immune function in man and in earlier studies the numbers of subjects studied have been small and, therefore, it is, as yet, not possible to draw firm conclusions. Also in earlier studies matched control groups were usually not included, making the interpretation of the findings even more difficult. In a retrospective study of 100 apparently healthy subjects over the age of 60 years, a relationship was found between serum vitamin E levels and the incidence of infections, subjects with the highest vitamin E levels (greater than 13.5 mg/l) having the lowest number of infections (Chavance et al. 1985). Baehner et al. (1977) supplemented three subjects with 1600 mg vitamin E/d and reported improved