Vitamin

Vitamins are organic compounds required in small amounts for normal metabolism, growth, and health. Most cannot be synthesized in sufficient quantities by the human body and must be obtained from the diet, although some are produced endogenously in limited amounts (for example, vitamin D is formed in the skin upon sun exposure, and certain B vitamins can be produced by gut microbes).

Vitamins are commonly classified as fat-soluble (A, D, E, K) and water-soluble (the B vitamins and vitamin C). Fat-soluble vitamins are stored in body tissues and can accumulate to toxic levels with excessive intake, whereas water-soluble vitamins are not stored to the same extent and excess amounts are usually excreted in urine, though high-dose supplements can cause adverse effects.

Roles vary widely. Many vitamins act as coenzymes in energy metabolism and macronutrient utilization; others function as antioxidants or support vision, bone health, blood clotting, immune function, and gene expression. Dietary sources include fruits, vegetables, grains, dairy products, meat, and fortified foods.

Deficiency can lead to specific diseases, such as scurvy from vitamin C deficiency, rickets or osteomalacia from vitamin D deficiency, xerophthalmia from vitamin A deficiency, and the classic B-complex deficiencies (e.g., thiamin, riboflavin, niacin) producing characteristic syndromes. Prevention generally relies on a balanced, varied diet, with targeted supplementation for at-risk groups when appropriate.

Historically, vitamins were identified in the early 20th century as essential dietary factors; the term vitamin originates from vital amine, though not all vitamins are amines. Supplements are common in certain populations but should be used judiciously to avoid toxicity and interactions with medications.