A vitamin is a compound that is required for the maintenance and growth of the human body. At any given moment countless chemical reactions take place in the body and these reactions are dependent on vitamins to get them going and keep them moving in the proper direction. There are 13 vitamins essential for humans, most of which must be obtained through the diet. These vitamins fall into two categories; water-soluble and fat-soluble. A lack of proper vitamins in the diet can lead to a variety of deficiency diseases.
Types
There are nine water-soluble and four fat-soluble vitamins. Once consumed, the fat-soluble vitamins, vitamins A, D K and E, are stored in the fat of the body until they are needed. The water-soluble vitamins, which dissolve easily in water, are not stored in the body and must be eaten on a regular basis. These water-soluble vitamins are grouped functionally into the B-complex vitamins and vitamin C (ascorbic acid). The B-complex vitamins consist of thiamine (B1), riboflavin (B2), niacin (B3), Pantothenic acid (B5), pyridoxine (B6), biotin, cobalamin (B12) and folic acid.
Function
Each essential vitamin has many distinct roles in the body. Vitamins function as co-enzymes in chemical reactions, that is, they activate or speed up a reaction. For example, the B-complex vitamins participate in reactions which process food into energy, help the nervous system function and maintain healthy skin, nail and liver cells. Vitamin A protects the body from toxins, supports immunity, helps the skin heal and is needed for vision. Vitamin D supports bone growth and maintenance. Vitamin E stabilizes cell membranes and removes toxic chemicals from the system. Vitamin K works in the blood to form blood clots. Vitamin C works in the immune system and supports collagen production in the connective tissues.
Sources
The fat-soluble vitamins are stored in fat and therefore are obtained in foods with high fat content like nuts, dairy, liver, fish and egg yolks. Vitamin K is also present in green plants and yogurt. Vitamin D can be made by the body when skin is exposed to UV light, and orange or yellow fruits and vegetables are a source of vitamin A.
The water-soluble vitamins are present in a large variety of food, especially fresh fruits and vegetables. Brewer's yeast, whole grains, nuts, liver, legumes and milk all have high quantities of the B-complex vitamins.
Deficiencies
If the essential vitamins are lacking in the diet a deficiency will develop. Because fat-soluble vitamins are stored in the body they are deficient with less frequency than water-soluble vitamins. A disease called scurvy, for example, is the direct result of a lack of vitamin C in the diet. To prevent the onset of deficiency disease a recommended dietary allowance, or RDA, has been established for each essential vitamin.
Considerations
Just as too little of a vitamin can result in illness, so can too much. Toxicity from a vitamin is much more common with fat-soluble vitamins since any excess consumed is stored for later use. Vitamin A is the most common cause of vitamin toxicity because it is not excreted quickly once consumed. Too much vitamin A can result in brain swelling, digestive upset, stunted growth, liver issues or dry skin. Over-consumption of any other vitamin may also result in toxicity, although toxicity from water-soluble vitamins is uncommon.
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