Vitamins are organic compounds which are needed in small quantities to sustain life. We get vitamins from food, because the human body either does not produce enough of them or none at all. An organic compound contains carbon. When an organism cannot produce enough of an organic chemical compound that it needs in tiny amounts, and has to get it from food, it is called a vitamin.
Sometimes the compound is a vitamin for a human but not for some other animals. For example, vitamin C (ascorbic acid) is a vitamin for humans but not for dogs, because dogs can produce (synthesize) enough for their own needs, while humans cannot. A vitamin is both an organic compound and an essential nutrient the body cannot produce enough of on its own, so it has to get it (tiny amounts) from food. There are currently 13 recognized vitamins. According to Medilexicon's medical dictionary, a vitamin is one of a group of organic substances, present in minute amounts in natural foodstuffs that are essential to normal metabolism; insufficient amounts in the diet may cause deficiency diseases. There are fat-soluble and water-soluble vitamins. Fat-soluble vitamins are stored in the fat tissues of our bodies, as well as the liver. Fat-soluble vitamins are easier to store than water-soluble ones, and can stay in the body as reserves for days, some of them for months. Water-soluble vitamins do not get stored in the body for long - they soon get expelled through urine. Water-soluble vitamins need to be replaced more often than fat-soluble ones. Vitamins A, D, E and K are fat-soluble. Vitamins C and all the B vitamins are water-soluble. Fat-soluble vitamins are absorbed through the intestinal tract with the help of fats (lipids).
Another name for Vitamin A is retinol and its deficiency may cause night-blindness and keratomalacia. Liver, carrot, sweet potato and pumpkin are some sources of Vitamin A. Thiamine is chemical name for...