Vitamins are organic compounds required by humans as nutrients in small amounts known as micronutrients. The term vitamin is derived from the Latin words ‘vital’ and ‘amine’, because vitamins are required for life and were originally thought to be amines.
As most of the vitamins cannot be produced by humans, they must be obtained from the diet. An organic compound is considered a vitamin if a lack of that compound in the diet results in overt symptoms of deficiency.
Vitamins are classified as either water-soluble or fat-soluble. In humans there are 13 vitamins: 4 fat-soluble (A, D, E and K) and 9 water-soluble (8 B vitamins and vitamin C). While fat-soluble vitamins are stored in the body’s fatty tissue, water-soluble vitamins must be used by the body right away. Any left over water-soluble vitamins leave the body through the urine. Vitamin B12 is the only water-soluble vitamin that can be stored in the liver for many years.
Vitamins are essential to life and healthy living. Failing to get the necessary amounts of specific vitamins can cause deficiency states that are unhealthy and even dangerous. Thus, a sufficient intake of vitamins is crucial to prevent the development of deficiency-related diseases. In addition, some vitamins have a considerable potential in health promotion and disease treatment.
Vitamin A is a term for a large number of related compounds (e.g., retinol, retinal, retinoic acid), which are known as ’retinoids’.
The vitamin A form found in foods that come from animals is retinol, mostly as retinylesters (also called ’preformed vitamin A’), a yellow, fat-soluble vitamin, and the precursor of the most active form of vitamin A (retinoic acid) used in the body.
The vitamin A form found in fruits and vegetables is called ’provitamin A carotenoid’ (e.g. beta-carotene, beta-cryptoxanthin), which can be converted into retinol in the body.
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