Vitamin C

1. Vitamin C (Ascorbic Acid)

Vitamin C (ascorbic acid and L-ascorbic acid) is a vitamin found in food and used as a dietary supplement. As a supplement, it is used to treat and prevent scurvy. Evidence does not support use in the general population for the prevention of the common cold. It may be taken by mouth or by injection. It is generally well tolerated. Large doses may cause gastrointestinal upset, headache, trouble sleeping, and flushing of the skin. Normal doses are safe during pregnancy. Vitamin C is an essential nutrient involved in the repair of tissue. Foods that contain vitamin C include citrus fruit, tomatoes, and potatoes.

Vitamin C was discovered in 1912, isolated in 1928, and first made in 1933. Medical uses for Vitamin C include scurvy, cancer prevention, heart disease prevention, and reduced duration of colds and illness.

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As vitamin C enhances iron absorption, iron poisoning can become an issue for people with rare iron overload disorders, such as haemochromatosis. A genetic condition that results in inadequate levels of the enzyme glucose-6-phosphate dehydrogenase (G6PD) can cause sufferers to develop hemolytic anemia after ingesting specific oxidizing substances, such as very large doses of vitamin C.

Vitamin C is an essential nutrient for certain animals, including humans. Vitamin C describes several vitamers that have vitamin C activity in animals, including ascorbic acid and its salts, and some oxidized forms of the molecule like dehydroascorbic acid. When either of these is introduced into cells, ascorbate and ascorbic acid are both naturally present in the body since the forms interconvert according to pH.

Vitamin C is a cofactor in at least eight enzymatic reactions, including several collagen synthesis reactions that, when dysfunctional, cause the most severe symptoms of scurvy. In animals, these reactions are especially important in wound-healing and in preventing bleeding from capillaries. Ascorbate also acts as an antioxidant, protecting against oxidative stress. The biological role of ascorbate is to act as a reducing agent, donating electrons to various enzymatic and a few non-enzymatic reactions.

term to know

Vitamin C

A vitamin found in food and used as a dietary supplement. It is used to treat and prevent scurvy. It is also known as ascorbic acid and L-ascorbic acid.

1a. Vitamin C Deficiency

Scurvy is an avitaminosis resulting from lack of vitamin C, since without this vitamin, the synthesized collagen is too unstable to perform its function. Scurvy leads to the formation of brown spots on the skin, spongy gums, and bleeding from all mucous membranes. The spots are most abundant on the thighs and legs, and a person with the ailment looks pale, feels depressed, and is partially immobilized. In advanced scurvy, there are open, suppurating wounds and loss of teeth and, eventually, death.

The human body can store only a certain amount of vitamin C, and so the body's stores are depleted if fresh supplies are not consumed. The time frame for onset of symptoms of scurvy in unstressed adults on a completely vitamin C free diet, however, may range from one month to more than six months, depending on previous loading of vitamin C.

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Western societies generally consume far more than sufficient vitamin C to prevent scurvy. In 2004, a Canadian Community Health Survey reported that Canadians of 19 years and above have intakes of vitamin C from food of 133 mg/day for males and 120 mg/day for females; these are higher than the RDA recommendations. Notable human dietary studies of experimentally induced scurvy have been conducted on conscientious objectors during WWII in Britain and on Iowa state prisoners in the late 1960s to the 1980s. These studies both found that all obvious symptoms of scurvy previously induced by an experimental diet with extremely low vitamin C content could be completely reversed by additional vitamin C supplementation of only 10 mg a day.

In these experiments, there was no clinical difference noted between men given 70 mg vitamin C per day (which produced a blood level of vitamin C of about 0.55 mg/dl, about 1/3 of tissue saturation levels) and those given 10 mg per day. Men in the prison study developed the first signs of scurvy about 4 weeks after starting the vitamin C-free diet, whereas in the British study, six to eight months were required, possibly due to the pre-loading of this group with a 70 mg/day supplement for six weeks before the scorbutic diet was fed.

Men in both studies on a diet devoid, or nearly devoid, of vitamin C had blood levels of vitamin C too low to be accurately measured when they developed signs of scurvy, and in the Iowa study, at this time were estimated (by labeled vitamin C dilution) to have a body pool of less than 300 mg, with daily turnover of only 2.5 mg/day, implying an instantaneous half-life of 83 days by this time (elimination constant of 4 months).

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Scurvy

An avitaminosis resulting from lack of vitamin C, since without this vitamin, the synthesized collagen is too unstable to perform its function.

1b. Absorption, Transport, and Excretion of Vitamin C

Ascorbic acid is absorbed in the body by both active transport and simple diffusion. Vitamin C is found in high concentrations in immune cells and is consumed quickly during infections. How vitamin C interacts with the immune system is not fully understood; it has been hypothesized to modulate the activities of phagocytes, the production of cytokines and lymphocytes, and the number of cell adhesion molecules in monocytes.

1c. Daily Requirement of Vitamin C

The North American Dietary Reference Intake recommends 90 milligrams per day for adult men, 75 mg/day for adult women, and no more than 2 grams (2,000 milligrams) per day. A balanced diet without supplementation usually contains enough vitamin C to prevent scurvy in an average healthy adult, while those who smoke tobacco or are under stress require slightly more.

While plants are generally a good source of vitamin C, the amount in foods of plant origin depends on the precise variety of the plant, soil condition, climate where it grew, length of time since it was picked, storage conditions, and method of preparation. The following table is approximate and shows the relative abundance in different raw plant sources. Amounts are given in milligrams per 100 grams of fruit or vegetable and represent rounded averages from multiple authoritative sources:

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The richest natural sources are fruits and vegetables. Vitamin C is the most widely taken nutritional supplement and is available in a variety of forms, including tablets, drink mixes, and capsules. Vitamin C is absorbed by the intestines using a sodium-ion-dependent channel. It is transported through the intestine via both glucose-sensitive and glucose-insensitive mechanisms. The presence of large quantities of sugar either in the intestines or in the blood can slow absorption.