Those small amounts of vitamins that are essential for health and development cannot be made in the body; they must come from animal products, fruit and vegetables. Most vitamins act as co-enzymes or prosthetic groups in the active sites of enzymes, where biochemical reactions occur.
Vitamin A
Vitamin A, or retinol, found in milk, butter, liver and fish, forms rhodopsin, a chemical in the retina, or back of the eye, that is needed to see in dim light. Vitamin A maintain the functioning of epithelial tissue, which lines intestinal, respiratory and urinary tracts. Vitamin A has anti-infective properties. People who lack this vitamin have increased susceptibility to infection and a lowered immune response. The liver stores 80 to 90 percent of the body's vitamin A, according to the Merck Manual.
Vitamin B1
Vitamin B1, or thiamine, found in pork, liver and nuts, helps in blood formation and the metabolism of carbohydrates, fats, amino acids, glucose and alcohol. It also helps in the synthesis of the neurotransmitter acetylcholine and the hydrochloric acid needed in digestion.
Vitamin C
Vitamin C, or ascorbic acid, is found in fruit and green vegetables. It acts as an antioxidant in tissue growth and repair and facilitates recovery from burns. It takes part in the maturation of red blood cells and development of healthy gums.
Vitamin D
Vitamin D comes from animal products, especially fish oils, butter and eggs. Vitamin D3, or cholecalciferol, is synthesized in skin by exposure to direct sunlight, which led to the name "sunshine vitamin." Vitamin D functions to elevate serum calcium and phosphate levels. It is necessary for the formation of bones and helps in development of teeth.
Vitamin K
Vitamin K controls the formation of essential clotting factors in the liver. Vitamin K, one of the most important vitamins for improving bone density, serves as the glue that binds calcium into bone matrix; it also helps to prevent hardening of the arteries.
References
- "Harrison's Principles of Internal Medicine"; Dennis Kasper, M.D.; 2005
- Health Vitamins Guide: Vitamin A: Sources and functions in the body
- "Office Practice of Medicine;" William T. Branch; 2003.
- Merck Manual: Vitamins
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