1988; DeCosse et al., 1989; Greenberg et al., 1994; Hofstad et al., 1998; McKeown-Eyssen et al., 1988).
Summary. Overall, the epidemiological evidence for an effect of vitamin E on cancer risk is weaker than that for vitamin E and cardiovascular disease. Observational epidemiological studies provide only limited evidence for a protective association and only for some cancer sites. At present, the data from intervention trials are most suggestive for the ability of vitamin E to prevent prostate cancer, but only a single trial has yet been reported, and prostate cancer was not the primary endpoint of that study.
It has been established that several aspects of immune function decline with increasing age (Bendich, 1994). Moreover, supplementation with vitamin E is able to reverse these deficits in some individuals. Meydani et al. (1997) studied a total of 88 free-living, apparently healthy subjects at least 65 years of age, who were randomly assigned to a placebo group or to groups consuming 60, 200, or 800 mg/day of vitamin E for 235 days. Subjects in the upper tertile of serum α-tocopherol concentrations (greater than 48.4 µmol/L [2.08 mg/dL] or approximately twice normal values) after supplementation with 200 or 800 mg/day of vitamin E had higher antibody responses to hepatitis B vaccine and delayed-type hypersensitivity (DTH) skin response. The 200-mg/day group also had a significant increase in antibody titer to tetanus vaccine. Recently, Pallast et al. (1999) reported that supplementation with 100 mg/day of vitamin E for 6 months may improve cellular immune function in apparently healthy elderly, but that the effect may be more pronounced in certain subgroups such as those who were physically less active or those with low baseline DTH reactivity.
Five subjects with tropical sprue for 8 to 10 years were found to have an abnormal delayed hypersensitivity response as well (Ghalaut al., 1995). Moreover, their plasma vitamin E concentrations were approximately one-tenth of normal, and the subjects had a sensory neuropathy characteristic of vitamin E deficiency. Parenteral vitamin E therapy increased serum vitamin E concentrations to normal and improved neurological responses and response to the immune function skin test, suggesting that vitamin E may be important in immune function.
Whether or not increases in vitamin E intake have any effect on immune function in younger populations remains uncertain. How-