A vitamin is any of a group of complex organic substances essential, in small amounts, for the normal functioning of the body. There are 13 vitamins: A, C, D, E, K, B12, and seven grouped under the vitamin B complex. Apart from vitamin D, which the body can synthesize itself, vitamins must be obtained from the diet. For most healthy people, a balanced diet contains adquate amounts of all the vitamins and supplements are not necessary; in fact certain vitamins may be harmful if taken in excess. However, specific vitamin supplements may be recommended for certain groups, such as women who are planning a pregnancy or are pregnant and people who are taking drugs that interfere with vitamin function.

VITAMIN TYPES

Vitamins can be categorized as fat-soluble or water-soluble. Fat-soluble vitamins (A, D, E, and K) are absorbed with fats from the intestine into the bloodstream and are then stored in fatty tissue (mainly in the liver). Because body reserves of some of these vitamins last for several years, a daily intake is not usually necessary. Deficiency of a fat-soluble vitamin is usually the result of a disorder in which intestinal absorption of fats is impaired (malabsorption) or is due to having a poor diet for a prolonged period.

Vitamins C, B12, and those of the B complex are water-soluble. Vitamin C and B complex vitamins can be stored in the body in only limited amounts and are excreted in the urine if taken in greater amounts than needed. A regular intake is therefore essential to prevent deficiency. However, vitamin B12 is stored in the liver; these stores may last for years.

VITAMIN FUNCTIONS IN THE BODY

The role of all the vitamins is not fully understood. Most have several important actions on one or more body systems, and many are involved in the activities of enzymes.

Source: A-Z family medical encyclopedia by BMA

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