Supplements may help healthy people for a number of reasons. They can help prevent vitamin and mineral deficiencies when the diet is not adequate to provide all necessary nutrients. They can also provide amounts of nutrients larger than the diet can provide.

Larger amounts of some nutrients may help to protect against future disease. Many of these nutrients will be briefly discussed here. However, for more information, refer to individual nutrient articles.

People may consume diets that are deficient in one or more nutrients for a variety of reasons. The typical Western diet often supplies less than adequate amounts of several essential vitamins and minerals. Recent nutrition surveys in the U.S. have found large numbers of people consume too little calcium, magnesium, iron, zinc, and, possibly, copper and manganese.

Weight-loss, pure vegetarian, macrobiotic, and several other diets can also place some people at risk of deficiencies that vary with the type of diet. Certain groups of people are at especially high risk of dietary deficiencies.

Studies have found that elderly people living in their own homes, often have dietary deficiencies of vitamin A and vitamin E, calcium, and zinc, and occasionally of vitamin D, vitamin B1, and vitamin B2. Premenopausal women have been found often to consume low amounts of calcium, iron, vitamin A, and vitamin C.