Dietary supplements refer to products made up of one or more of the essential nutrients such as vitamins, minerals, and protein. The 1994 Dietary Supplement Health and Education Act (DSHEA) broadened the definition to include any product that was intended for ingestion as a supplement to the diet. This includes vitamins; minerals; herbs, botanicals, and other plant-derived substances; amino acids ( the building block of proteins), and concentrates, metabolites, constituents and extracts of these substances.

Dietary supplements come in many forms, including tablets, capsules, powders, soft gels, gelcaps, and liquids. A visit to your local health food store reveals aisles of vitamins, minerals, and herbs that make a variety of claims to improve overall health. Besides health food stores, dietary supplements are also sold in grocery, drug and national discount chain stores as well as through mail order catalogs, TV programs, the Internet and direct sales.

While some...