The Vitamin are substances that are needed in very small amounts each day to maintain normal metabolism. The term ‘vitamin’ comes from ‘vital amines’, coined by Dr Casimir Funk in 1913 when these essential nutrients were first discovered. Nutritionists at the beginning of the twentieth century had identified the major nutrients, i.e. carbohydrates, fats, and proteins, and recognized that several mineral elements were also essential for health. However, when animals were fed on diets containing purified mixtures of the known nutrients they failed to grow.
This was remedied by adding small amounts of milk to the diets, and further studies identified two factors in the milk. One, called A, was found in the cream and the second, called B, in the watery part of the milk. Factor B was identified as an amine hence the name.
As other different essential substances were identified it became apparent that these were not all amines, and the final ‘e’ was removed from the name.The naming of the vitamins was originally alphabetical, i.e. A, B, C, D, and E, but as chemical techniques became more sophisticated it was discovered that vitamin B was a mixture of substances with different functions, and the B vitamins were also given numbers, i.e. B1, B2, B6, and B12.
Gaps in the letter sequence relate to substances that were given numbers but later found not to be essential, or substances such as nicotinic acid (niacin) that had already been identified by a specific name and later discovered to be chemically the same as one of the B vitamins. Vitamin F turned out not to be a vitamin, vitamin G was the same as vitamin B2and vitamin H is known as biotin – another B vitamin....
The alphabetical sequence ends with H; vitamin K is not named in order of discovery but from the Danish term ‘koagulation’, relating to the function in the blood. The vitamins are by definition essential, and it was originally thought that they could not be made in the body. This is true for all but two of the vitamins, vitamin D and niacin, originally described as one of the B vitamins.
Vitamin D is made in the skin when it is exposed to sunlight and is therefore now considered to be a hormone, but it is essential if sunlight exposure is inadequate, e.g. in housebound people or for those who cover their skin for cultural reasons. Niacin is made in the body from the essential amino acid tryptophan, and deficiency is unlikely to occur except in very particular circumstances.
Vitamins are classified as fat soluble (A, D, E, and K) or water soluble (B vitamins and C). They have a wide range of functions in the body according to their structure and chemistry. Obvious deficiency diseases are rare in developed countries but subclinical deficiencies can occur under certain circumstances.
As the sciences of biochemistry and genetics have become more advanced, the case for supplementation to ‘optimum’ level has been put forward more strongly for certain vitamins such as vitamin C, folic acid, B6, and possibly B12. Vitamins A, C, and E have become known as the ‘antioxidant’ vitamins. These will be discussed in detail elsewhere in the book.
In high doses some vitamins can be toxic. This is most likely with fat-soluble vitamins, especially vitamin A, where high doses in early pregnancy can cause malformations in the fetus. Women are therefore advised not to eat liver in early pregnancy due to its high content of vitamin A.
Cases of vitamin D toxicity are rare, but in the post-war years when the vitamin was added to baby foods and given as a supplement, cases of hypercalcaemia (due to the vitamin’s effects on calcium absorption) were seen. Water soluble vitamins are less likely to cause problems because they are not generally stored in the body, but very high doses of vitamin C (over 2 g per day) will cause gastroin testinal upsets, and it has been suggested that vitamin B6 taken in very high doses to prevent menstrual symptoms in women may have ill-effects on the nervous system.
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