Key issues in nutrition. Disease prevention through adulthood and old age.

Certain dietary practices are valid methods of lowering the risk of disease. Others, while popular, have unproven benefits or may even be associated with risks of their own. Careful evaluation of hypercholesterolemia is necessary. Persons with a high level of low-density lipoprotein (LDL) cholesterol and a low level of high-density lipoprotein (HDL) cholesterol need diet therapy, because they are at increased risk of cardiovascular disease. Weight reduction and fat restriction can lower blood pressure, help control hyperglycemia, and improve the LDL cholesterol-HDL cholesterol ratio. Some evidence indicates a protective role of beta carotene against cancer in animals. However, hypervitaminosis A is dangerous and relatively easy to accomplish, so supplementation beyond a multivitamin tablet is discouraged. Data about inhibition of cancer in humans through use of high doses of vitamin E or C or selenium are inconclusive, and studies of effects of long-term ingestion are not available. In general, megadoses of even healthy substances are thought to be dangerous. Decreased consumption of fat, increased consumption of foods high in fiber, and elimination of alcohol and tobacco are sensible recommendations. Consumption of cruciferous vegetables has not been proven to reduce the incidence of cancer, but a moderate amount of them in the diet would seem reasonable.