Vitamin C blood serum levels are considered saturated at levels > 65 μmol/L (1.1 mg/dL), achieved by consuming amounts which are at, or above, the Recommended Dietary Allowance, while adequate levels are defined as ≥ 50 μmol/L. This enzyme utilizes ascorbate to neutralize excess hydrogen peroxide (H 2O 2) by converting it to water (H 2O) and oxygen. In plants, vitamin C is a substrate for ascorbate peroxidase.
These compounds can be restored to a reduced state by glutathione and NADPH-dependent enzymatic mechanisms. Doing so converts vitamin C to an oxidized state - either as semidehydroascorbic acid or dehydroascorbic acid. Another biochemical role of vitamin C is to act as an antioxidant (a reducing agent) by donating electrons to various enzymatic and non-enzymatic reactions. In humans, vitamin C deficiency leads to impaired collagen synthesis, contributing to the more severe symptoms of scurvy. Vitamin C functions as a cofactor in many enzymatic reactions in animals (including humans) that mediate a variety of essential biological functions, including wound healing and collagen synthesis. Oxidized forms of the molecule such as dehydroascorbic acid are converted back to ascorbic acid by reducing agents. Ascorbate and ascorbic acid are both naturally present in the body, since the forms interconvert according to pH. Ascorbate salts such as sodium ascorbate and calcium ascorbate are used in some dietary supplements. The term vitamin C encompasses several vitamers that have vitamin C activity in animals. Vitamin C is an essential nutrient for certain animals including humans.
Prolonged storage or cooking may reduce vitamin C content in foods. Foods containing vitamin C include citrus fruits, kiwifruit, guava, broccoli, Brussels sprouts, bell peppers and strawberries. Partly for its discovery, Albert Szent-Györgyi and Walter Norman Haworth were awarded the 1937 Nobel Prizes in Physiology and Medicine and Chemistry, respectively. Vitamin C is available as an inexpensive generic and over-the-counter medication. It is on the World Health Organization's List of Essential Medicines. Vitamin C was discovered in 1912, isolated in 1928, and, in 1933, was the first vitamin to be chemically produced.
The United States Institute of Medicine recommends against taking large doses. Large doses may cause gastrointestinal discomfort, headache, trouble sleeping, and flushing of the skin. It may be taken by mouth or by injection. It is unclear whether supplementation affects the risk of cancer, cardiovascular disease, or dementia.
There is some evidence that regular use of supplements may reduce the duration of the common cold, but it does not appear to prevent infection. Most animals are able to synthesize their own vitamin C, although humans, the other great and lesser apes, monkeys (but not all primates), most bats, some rodents, and certain other animals must acquire it from dietary sources. It is required for the functioning of several enzymes and is important for immune system function. Vitamin C is an essential nutrient involved in the repair of tissue and the enzymatic production of certain neurotransmitters. Vitamin C (also known as ascorbic acid and ascorbate) is a vitamin found in various foods and sold as a dietary supplement.
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