Vitamins – types and functions
Vitamins are special organic substances which are indispensable for the organism. They do not provide energy and are distinct from the main components of food (for example, proteins, carbohydrates, fats, mineral salts and water), but they participate in metabolism as catalysts. They are necessary for the formation of tissue enzymes which influence the transformation of substances in the cells and tissues of the organism. N. Lunin, a Russian doctor, was the first to establish (in 1880) the presence of these substances (later named vitamins) in the food. About 20 vitamins are known today. They are marked by letters A, B, C, D, E, K, P, etc. The chemical composition and physiological role of most vitamins have already been determined. Some vitamins are water soluble (B and C), while others are soluble only in fats (A, E, K). The daily requirements of vitamins are measured in milligrams and even parts of a milligram.
Foods differ greatly in the vitamins they contain. Fresh varied food usually contains enough vitamins for the organism.
- Vitamin A is found in green plants and is necessary for the proper growth of bones, for the nutrition of the cornea of the eye and for the proper functioning of night vision.
- Vitamin B is really a complicated group of vitamins, fifteen of which have now been identified. Some of these are necessary for growth, for the proper functioning of the nervous system, for the proper formation of erythrocytes.
- Vitamin C prevents scurvy and is found in fresh vegetables and in citrus fruits.
- Vitamin D prevents rickets, vitamin E deficiency may lead to infertility.
Prolonged deficiency of any vitamin results in a disease known as avitaminosis. Most avitaminoses are accompanied by reduced working capacity, rapid fatigue, reduced resistance of the organism to infection, incorrect development and retarded growth in children.
The commonest vitamin deficiency disease in Europehas undoubtedly been rickets (vitamin D deficiency). Examples of Vitamin deficiency diseases which are still common in other regions of the globe include beri-beri (in rice eating countries in the East) and pellagra (among populations subsisting on maize diets).