ABSTRACT
Vitamins are organic dietary substances necessary for the maintenance of normal metabolic function. Only small amounts of the vitamins are required for normal health. In the body, they act as components of the important enzyme systems that catalyze the reactions by which proteins, fats, and carbohydrates are metabolized. Some of the vitamins (e.g., vitamin K) may be formed by bacteria in the gut, whereas vitamin D is synthesized by exposure of the skin to sunlight. With these exceptions, vitamins must be ingested in the food. Restricted diets or disorders of the gastrointestinal tract, interfere with absorption, leading to vitamin deficiency. When pronounced, such deficiencies give rise to easily recognizable clinical syndromes (
beriberi
,
pellagra
,
rickets
,
scurvy
), which have long been recognized. Milder forms of avitaminosis are much more common and also give rise to disability and ill health (see Wilson, 2005; Berkner, 2005; Singh et al., 2005).
