Role of Vitamin E in Supplements
Vitamin E deficiency is associated with impaired immune responsiveness and increased severity of infection. Vitamin E deficiency has resulted in impaired bactericidal activity of phagocytes, reduced lymphocyte response to mitogens, decreased production of the cytokine IL-2, altered T cell differentiation in the thymus, and increased myocardial injury during viral infection.
Supplementation with vitamin E during viral or bacterial infection (influenza, murine AIDS, herpes simplex virus, Staphylococcus aureus, parainfluenza, Clostridium pelfringens) has been shown to decrease mortality rate or severity of infection in several different animal models. However, not all studies have found an improved resistance to infection from vitamin E supplementation 85 and we are not aware of any human studies that have tested this theory by infecting human subjects and then assessing disease incidence and/or severity.
It is less clear whether intake of vitamin E above the RDA enhances resistance to infection in healthy individuals. The most promising results have come from studies involving elderly human subjects. In several randomized controlled trials, various doses of vitamin E were administered to elderly individuals for different periods of time and immune responses were measured.
Two studies that administered supplements (100-800 mg/day) for at least 6 months found an enhancement of several immune parameters including dihydrotestosterone (DTH) response, mitogen-induced IL-2 production, and increased antibody titer to hepatitis B and tetanus vaccine One of these studies found optimal results in those subjects receiving 200 mg/day of vitamin E, but higher levels of vitamin E (800 mg/day) were not associated with an additional improvement of immune response.
The results from one study failed to find an enhancement of immune response in elderly subjects consuming 100 mg/day. However, in this study, subjects received the supplement for only 3 months and perhaps a longer period of supplementation is necessary to observe an effect. The results from two additional studies found enhancement of several immune parameters (LPS-induced production of IL-1, TNFa, mitogen-induced lymphocyte proliferation, neutrophil phagocytosis) when vitamin C (1 g/day) and vitamin E (200-400 mg/day) were administered to healthy young and elderly adults. The mechanisms by which vitamin E supplementation may alter immune response remain to be established.
Currently, it is thought that one potential mechanism may involve the production of prostaglandin E 2 (PGE 2 ). PGE 2 , produced by macrophages, is known to suppress some lymphocyte responses. Some recent evidence suggests that aged animals fed additional vitamin E have a reduction of macrophage PGE 2 production. The immune response may be enhanced through the reduction of PGE 2. Further research on potential mechanisms will provide important information with respect to an understanding of vitamin E-associated immunomodulation. T
he findings from these studies show promise with respect to vitamin E supplementation and enhanced immune function, particularly in the elderly. However, we are not aware of any randomized clinical trials that have shown a decreased incidence of infection in association with vitamin E supplementation alone (without other vitamins or trace nutrients). The findings from one of the studies suggested a trend (p = 0.098, not statistically significant) towards reduced incidence of infectious disease in the elderly.
The results from animal studies suggest that in some instances, the incidence of disease is reduced with vitamin E supplementation. A reduced incidence of infection, however, was observed in chickens consuming diets supplemented with vitamin E. One study involving calves did not find a reduction in disease incidence in those animals fed additional vitamin E. Thus, the results from animal studies are similar to the human studies in that a beneficial effect of vitamin E supplementation has been found, although the finding is not consistent. At this time, the results regarding vitamin E supplementation and immunity in the elderly human population are promising. However, additional large-scale randomized controlled trials are necessary before it is possible to determine whether vitamin E supplementation results in reduced susceptibility to infection.
Immune Effects and Exercise
Although vitamin E has been studied in relation to exercise, most studies have focused on the potential antioxidant effects of vitamin E supplementation. Others have examined various physiological changes regarding vitamin E supplementation and exercise and found no change in neuroendocrine profile but a slight reduction in the incidence of gastrointestinal complications in those marathon runners consuming vitamin E for 2 weeks before the race. The only study we are aware of that examined immunity and vitamin E supplementation with exercise found that vitamin E and C supplementation before competing in an ultramarathon reduced the incidence of URI symptoms in the postrace period.
However, it was thought that this effect was related to vitamin C rather than vitamin E because the post-race reduction in symptoms of URI was not lower with vitamin E + C than vitamin C alone. To our knowledge, we are not aware of any studies that have explored potential associations between vitamin E supplementation alone and immune response in regards to exercise. PerÂhaps this area of research may show some promise in the elderly.