The vitamins

Vitamins are a heterogeneous group of substances and are vital nutrients that must be obtained from the diet. Although a number of these were termed vitamins between the 1930s and 1950s, nutritional science now recognises only 13 substances, or groups of substances, as being true vitamins. The 13 substances are divided into two categories, the fat-soluble vitamins of which there are four (vitamins A, D, E and K) and the water-soluble vitamins of which there are nine (vitamins C, Bj, B2, B6, B12, niacin, pantothenic acid and biotin). They are listed in Table 10.1. Even within the two sub-categories, the vitamins have almost no common attributes in terms of chemistry, function or daily requirements. In terms of requirements some, such as vitamins C, E and niacin, are needed in tens of

Table 10.1 Vitamins and some commonly used synonyms

Vitamin

Synonyms

Fat-soluble vitamin A vitamin D2 vitamin D3 vitamin E vitamin K1 vitamin K2 vitamin K3

retinol ergocalciferol cholecalciferol alpha, beta and gamma tocopherols and alpha tocotrienol phylloquinone, phytomenadione farnoquinone, menaquinone menadione

Water-soluble vitamin B1 vitamin B2 vitamin B6 vitamin B12 niacin niacinamide pantothenic acid folic acid biotin vitamin C

thiamin riboflavin pyridoxal, pyridoxine, pyridoxamine cobalamins, cyanocobalamin, hydroxocobalamin nicotinic acid (vitamin PP) nicotinamide (vitamin PP)

folacin (vitamin M) vitamin H ascorbic acid milligrams a day whilst others, such as vitamins D and B12, are only needed in single microgram amounts. It can be seen from these examples that there is no relationship between the form of delivery (i.e. fat or water soluble) and the daily requirements. The heterogeneity also applies to the chemical structure and the functions of the vitamins. Chemically, there are no similarities between the substances. Some are single substances such as biotin, whilst others, such as vitamin E, are groups of compounds all exhibiting vitamin activity.

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