Physiological function of ascorbic acid

1. Physiological function of ascorbic acid The physiological function of ascorbic acid largely depends on the redox properties of this vitamin. L - ascorbic acid is a cofactor of hydroxylase and monooxygenase, which are involved in the synthesis of collagen, carnitine and neurotransmitter. Ascorbic acid accelerates the hydroxylation reaction by making the active center of metal ions in a reduced state, so as to optimize the activity of enzyme hydroxylase and oxygenase. Ascorbic acid plays an important role in maintaining collagen, which accounts for about one third of the whole body protein. It constitutes the main protein of skin, bone, tooth, cartilage, tendon, blood vessel, heart valve, intervertebral disc, cornea and eye lens. Ascorbic acid is necessary to maintain the activity of prolyl enzyme and lysine hydroxylase. The hydroxylation of proline and lysine is carried out by proline hydroxylase with ascorbic acid as a cofactor. The lack of ascorbic acid reduced the hydroxylation of proline and lysine, thus affecting the synthesis of collagen. Ascorbic acid is a synthetic carnitine（ β- Hydroxybutyric acid). Carnitine is necessary for the transportation and transfer of fatty acids to mitochondria, where carnitine can be used to produce energy. Ascorbic acid is a cofactor of hydroxylation in carnitine synthesis. In addition, ascorbic acid is dopamine- β- The cofactor of hydroxylase, which catalyzes the conversion of neurotransmitter dopamine to norepinephrine. Therefore, ascorbic acid is necessary for the synthesis of catecholamine. In addition, ascorbic acid catalyzes other enzyme reactions including amidation, which is necessary for the maximum activity of oxytocin, antidiuretic hormone, cholecystokinin and melanin tripin. Ascorbic acid is also necessary for the conversion of cholesterol to bile acid, because it regulates microsomal 7 α- Hydroxylation, which is the rate limiting reaction of cholesterol catabolism in the liver. In the case of ascorbic acid deficiency, this reaction will slow down, leading to the accumulation of cholesterol in the liver, hypercholesterolemia, cholesterol gallstone formation, etc. Ascorbic acid and iron It is well known that ascorbic acid can enhance the availability and absorption of iron from non heme iron sources. Studies have found that ascorbic acid supplementation can promote the absorption of iron in the diet. It has been suggested that ascorbic acid be used to reduce iron in order to increase the absorption of non heme iron in the diet. It is well known that in the presence of redox active iron, ascorbic acid acts as an oxidant in vitro, which may contribute to the formation of hydroxyl radicals and eventually lead to the oxidation of lipids, DNA or proteins.

2. Therefore, ascorbic acid supplementation may be harmful to some premature infants with high iron content or high bleomycin detectable iron content (BDI), because it may cause oxidative damage to biological molecules. However, no oxidative effect of ascorbic acid supplementation on DNAdamage was observed in the presence or absence of iron. Role of ascorbic acid in health and disease Ascorbic acid and common cold The best known health benefit of ascorbic acid is the prevention or relief of the common cold. Pauling suggested that taking 1-2 grams of ascorbic acid can effectively prevent/improve the common cold. The role of oral vitamin C in the prevention and treatment of colds remains controversial, despite many controlled trials. Several clinical trials with different doses of ascorbic acid showed that ascorbic acid had no obvious preventive effect, but it reduced the severity and duration of cold symptoms during infection. The randomized and non randomized trials on the prevention or treatment of common cold with vitamin C showed that the intake of up to 1.0 g ascorbic acid per day in winter months had no consistent beneficial effect on the incidence rate of common cold. In the prevention and treatment trials, there is a consistent beneficial but generally moderate therapeutic effect on the duration of cold symptoms. There is no clear indication of the relative benefits of different vitamin C doses. However, in the test of vitamin C after cold symptoms, there is some evidence that high-dose vitamin C is more beneficial than low-dose vitamin C. There has been a long debate on the role of ascorbic acid in enhancing immunity during cold infection. Ascorbic acid has been shown to stimulate the immune system by enhancing t cell proliferation in response to infection. These cells can control the inflammatory reaction by producing a large number of cytokines and helping B cells to synthesize immunoglobulin, thus dissolving the infected target cells. In addition, previous studies have shown that ascorbic acid blocks the pathway leading to T cell apoptosis, thereby stimulating or maintaining T cell proliferation to attack infection. This mechanism is believed to be an enhanced immune response observed after taking vitamin C during cold infection.