Vitamin C, also called ascorbic acid, is a major nutrient active in the growth and repair of body tissues. It is also thought to play a role in immune function. Vitamin C is a water-soluble vitamin—that is, a vitamin that dissolves readily in water. It is easily absorbed in the small intestine and throughout the bloodstream and tissues. Vitamin C is not stored in the body and is readily removed in the urine. Plants and most animals can produce vitamin C, but humans cannot. Individuals should therefore eat foods that contain the vitamin daily.
Common food sources of vitamin C are fresh fruits and vegetables . Citrus fruits and juices are particularly rich sources. Vitamin C levels decrease over time in stored food. Cooking also destroys vitamin C, lowering the amount in foods.
Function.
Vitamin C functions as a coenzyme and cofactor, assisting in many chemical reactions in the body, including the formation of collagen . Collagen is a protein that strengthens and gives shape to connective tissue , such as ligaments and tendons , and to bone . Collagen also provides much of the strength and flexibility in skin and in blood vessels. Vitamin C therefore plays a key role in wound healing. It is also necessary for the production of certain hormones . Vitamin C functions as antioxidant , a substance thought to protect body cells from damage caused by unstable molecules called free radicals. Vitamin C is also involved in the recycling of other antioxidants. People who smoke cigarettes require higher levels of vitamin C to help prevent cell damage from free radicals produced by smoking . Vitamin C also enhances the absorption of the mineral iron in the small intestine.
Medical researchers believe vitamin C has a role in the function of the immune system. The vitamin has long had a reputation for helping to fight the common cold . However, researchers have not been able to prove that vitamin C prevents people from getting colds. Some scientists believe that taking vitamin C supplements at the beginning of a cold may decrease the severity of cold symptoms.
Intake.
The United States National Academy of Medicine, a branch of National Academies , has established a tolerable upper intake level (UL) of vitamin C at 2000 milligrams. Regular consumption of vitamin C above this level may cause health problems, including diarrhea and kidney stones .
The continued lack of a particular vitamin can result in a vitamin deficiency disease. Disease caused by a lack of vitamin C is called scurvy . It can develop after about one month with no vitamin C in the diet. People at risk of vitamin C deficiency include the elderly, ill patients with chronic stress, and people who abuse alcohol. Symptoms of scurvy relate to vitamin C’s role in collagen production. They include abnormal bleeding , inflamed gums, weakness of connective tissue, poor wound healing, and neurological (nervous system) changes.
History.
In the past, scurvy was often seen among sailors, who were likely to spend months at sea without consuming any fresh fruits or vegetables. In 1747, the Scottish physician James Lind was serving as a surgeon for the British Navy. He discovered that eating oranges and lemons was an effective treatment for scurvy. Lind produced A Treatise on Scurvy, published in 1754, describing his discovery. In 1795, the British Navy followed his advice and began issuing daily rations of citrus juice to its men.
The British chemist Sir Walter Haworth determined the chemical structure of vitamin C in 1933. The structure is derived from hexose, a kind of carbohydrate.
