One of the most exciting areas of nutrition research is the study of vitamins and antioxidants. That vitamins are essential nutrients has been known for a long time. Amounts needed to perform vital functions are relatively small. As a rule vitamins promote the actions of enzymes to make them work more efficiently. In this role they are called coenzymes. Much research has been carried out to determine minimal amounts of vitamins that are needed to perform their necessary action.
Once this amount has been determined it is possible to make a recommendation about how much of the vitamin should be consumed each day. This value is called the recommended dietary allowance (RDA). The Food and Nutrition Board of the Institute of Medicine sets the RDAs. The RDAs are used to define the food requirements of government programs, to develop food labeling by the Food and Drug Administration, to produce the Dietary Guidelines for Americans, and to advise patients on good nutrition to prevent or treat disease. The Food and Nutrition Board has recently published new RDAs for B vitamins and antioxidant vitamins.
A persistent question in nutrition has been whether intakes of vitamins above the RDAs can provide extra health benefits. Expert opinion on this question is divided. Some researchers believe that the RDA is the upper limit of benefit; others contend that higher intakes provide added value. An enormous industry has developed to capitalize on the idea that higher intakes of vitamins are beneficial. Vitamin enriched products are sold as dietary supplements.
Although the predominance of expert opinion some years ago were that extra vitamins are expensive and unnecessary, there has been some change in thinking. The essential concept is as follows. The published RDAs for vitamins provide protection against acute deficiency diseases, e.g. scurvy, pellagra, beriberi, and pernicious anemia. Yet it is possible that higher intakes may protect against chronic diseases such as coronary heart disease and cancer. Various plausible hypotheses have been developed whereby long-term protection might occur. These hypotheses have generated intensified research into the vitamin field.
Much of this research has focused on the vitamins with antioxidant properties. The essential concept is that chronic diseases are caused at least in part by excessive oxidation. Of course, oxidation is essential for survival. The burning of nutrient fuel (fats and carbohydrates) to provide energy for bodily functions occurs by oxidation. A constant supply of oxygen is required by the body for these oxidative processes. Even so, if oxidation precedes too vigorously, damage to body molecules and tissues can occur. This damage is particularly likely to occur when oxidation occurs by highly reactive oxygen molecules called free radicals. If the body's DNA is damaged by free radicals and is not repaired, the long-term risk for cancer is increased. If the lipoprotein called LDL ("the bad cholesterol") is damaged by free radicals, cholesterol deposition in arteries (atherosclerosis) may be increased. These hypothetical consequences of free-radical damage has led researchers to wonder whether natural antioxidants that destroy free radicals might protect against disease. One antioxidant vitamin is Vitamin C (ascorbic acid). It is soluble in water and can readily enter cells and tissues. Studies have shown that Vitamin C has some antioxidant properties when given to humans; this action is enhanced when Vitamin C is taken in amounts that exceed the RDA. Investigations in laboratory animals provide additional evidence of protection against molecular damage. Studies in large populations suggest that high intakes of vitamin C are associated with reduced risk for several chronic diseases. In spite of this suggestive evidence, other studies have failed to document benefit in disease reduction from extra vitamin C. The RDA for Vitamin C was recently increased by the Food and Nutrition Board, but it is still below what some investigators believe would be beneficial.
Another antioxidant vitamin is Vitamin E (alpha tocopherol). It is a fat-soluble vitamin. Again there is evidence of benefit from high intakes of Vitamin E. Studies in both animals and human populations are consistent with protection against chronic disease. Yet recent clinical trials of high intakes of Vitamin E do not convincingly show a benefit. Several studies indeed have been negative. For this reason, the Food and Nutrition Board has not recommended high intakes of Vitamin E for the prevention of disease.
For the past decade the Center for Human Nutrition has been carrying out in-depth research on antioxidant vitamins to evaluate their potential for the prevention for chronic disease. These studies have been spear headed by Dr. Ishwarlal (Kenny) Jialal and his laboratory. Dr. Jialal has demonstrated that high intakes of Vitamin E will reduce the oxidation of LDL ("the bad cholesterol"). This effect could slow down the development of coronary atherosclerosis. In addition, Dr. Jialal and associates have found that Vitamin E have favorable effects on the functions of cells involved in the formation of atherosclerosis. This research is particular seminal, and it has generated great interest in the antioxidant field. Although Dr. Jialal has studied several vitamins and antioxidants, Vitamin E has emerged as the most promising.
Page Last Updated: June 26, 2006
