Nutrients and Disease Prevention
As discussed earlier, consumption of fruits and vegetables has a strong protective association with various types of cancer. We still do not know which substances in these foods are responsible for the anticarcinogenic action. Although most attention has hitherto been directed to p-carotene, other substances likely play more important roles, especially phytochemicals. One class of possibly anticarcinogenic phytochemicals is soy isoflavones. The phytoestrogenic action of these substances and how they may be protective against breast cancer (and CHD) is explored by Wilson and Murphy. Similarities between these phytoestrogens and pharmacological estrogen agonists continue to blur the differences between foods and drugs.
With a better understanding of the anticarcinogenic potential of such substances as phytochemicals, folate, and selenium, it should be possible to produce a supplement that provides an effective, safe, and cheap way to prevent a great many cases of cancer. Vitamin C has a negative association with various conditions, including cataracts, asthma, and loss of pulmonary function. As in the case of p-carotene and cancer, it is critically important to bear in mind that what these data really reveal is not that vitamin C protects against these conditions, but rather that ascorbater-ich fruit and vegetables do.
As with cancer, therefore, once the responsible substances have been identified, we can better understand how to enrich our dietary intake, perhaps using supplements, so as to prevent these conditions. A nutrient that merits further investigation is vitamin E. There is evidence that it may have some prophylactic effectiveness against cancer and CHD. These benefits are generally seen only at intakes several times higher than the RDA. These levels cannot be achieved through food consumption alone. This suggests that vitamin E is acting as a nutraceutical rather than as a vitamin.
We have growing evidence that optimal dietary intake (especially vitamin E) may enhance immune function and thereby reduce the burden of infectious disease. Clarification of these relationships may be of enormous value, especially to the elderly and malnourished and to populations at high risk of infectious disease.
