What is rda of vitamin c

A much larger study of 19, people, including 4, children from 6 to 16 years of age, found higher serum vitamin C concentrations to be associated with significantly lower blood lead concentrations A US national survey of more than 10, adults found that blood lead concentrations were inversely related to serum vitamin C concentrations Cigarette smoking or second-hand exposure to cigarette smoke contributes to increased blood lead concentration and a state of chronic low-level lead exposure.

The mechanism s by which vitamin C reduces blood lead concentration is not known, yet it has been proposed that vitamin C could inhibit intestinal absorption or enhance urinary excretion of lead Unlike plants and most animals, humans have lost the ability to synthesize vitamin C endogenously and therefore have an essential dietary requirement for this vitamin see The Recommended Dietary Allowance.

The national study identified smokers and those of lower socioeconomic status to both be at higher risk for vitamin C deficiency Vitamin C L-ascorbic acid is available in many forms, but there is little scientific evidence that any one form is better absorbed or more effective than another.

Most experimental and clinical research uses ascorbic acid or its sodium salt, called sodium ascorbate. Natural and synthetic L-ascorbic acid are chemically identical and there are no known differences regarding biological activities or bioavailability Mineral salts of vitamin C are considered less acidic than vitamin C and therefore are considered "buffered.

Sodium ascorbate and calcium ascorbate are the most common forms, although a number of other mineral ascorbates are available. Sodium ascorbate provides mg of sodium mg of ascorbic acid per 1, mg of sodium ascorbate, and calcium ascorbate generally provides 90 to mg of calcium mg of ascorbic acid per 1, mg of calcium ascorbate.

Flavonoids are a class of water-soluble plant pigments that are often found in vitamin C-rich fruit and vegetables, especially citrus fruit and berries see the article on Flavonoids. There is little evidence that the flavonoids in most commercial preparations increase the bioavailability or efficacy of vitamin C Some, yet not all, studies in animal models such as vitamin C-deficient guinea pigs or genetically scorbutic rats found an increased uptake of vitamin C in peripheral circulation and specific organs in the presence of flavonoids.

However, studies conducted in humans found no differences in bioavailability of vitamin C from flavonoid-rich whole fruit or fruit juice and synthetic vitamin C reviewed in Ascorbyl palmitate is a vitamin C ester i. In this case, vitamin C is esterified to the saturated fatty acid , palmitic acid, resulting in a fat-soluble form of vitamin C.

Ascorbyl palmitate has been added to a number of skin creams due to interest in its antioxidant properties, as well as its importance in collagen synthesis see the separate article, Vitamin C and Skin Health Although ascorbyl palmitate is also available as an oral supplement, most of it is likely hydrolyzed to ascorbic acid and palmitic acid in the digestive tract before it is absorbed One small placebo -controlled, cross-over trial in 11 men showed that the oral administration of 4 g of vitamin C resulted in a greater vitamin C concentration in plasma over a four-hour period when vitamin C was encapsulated in liposomes compared to unencapsulated vitamin C Although liposomal encapsulation could increase vitamin C bioavailability , plasma vitamin C concentrations were much lower than those achieved with intravenous vitamin C administration For a more detailed review of scientific research on the bioavailability of different forms of vitamin C, see The Bioavailability of Different Forms of Vitamin C.

A number of possible adverse health effects of very large doses of vitamin C have been identified, mainly based on in vitro experiments or isolated case reports , and include genetic mutations , birth defects, cancer, atherosclerosis, kidney stones , "rebound scurvy ," increased oxidative stress , excess iron absorption, vitamin B 12 deficiency, and erosion of dental enamel. The concern of kidney stone formation with vitamin C supplementation is discussed below.

A UL of 2 g 2, mg daily was recommended in order to prevent generally healthy adults from experiencing diarrhea and gastrointestinal disturbances Such symptoms are not generally serious, especially if they resolve with temporary discontinuation of vitamin C supplementation.

Because oxalate is a metabolite of vitamin C, there is some concern that high vitamin C intake could increase the risk of calcium oxalate kidney stones.

Some 24 , , , but not all , studies have reported that supplemental vitamin C increases urinary oxalate concentrations. Whether any increase in oxalate levels would translate to an elevation in risk for kidney stones has been examined in several epidemiological studies. On the other hand, two other large prospective studies reported that a high intake of vitamin C was associated with an increased risk of kidney stone formation in men , Specifically, the Health Professionals Follow-Up Study collected data on dietary and supplemental vitamin C intake every four years in 45, male health professionals ages years In the Cohort of Swedish Men study, self-reported use of single-nutrient vitamin C supplements taken seven or more times per week at baseline was associated with a two-fold higher risk of incident kidney stones among 48, men ages years followed for 11 years Despite conflicting results, it may be prudent for individuals predisposed to oxalate kidney stone formation to avoid high-dose vitamin C supplementation.

Overall, evidence suggesting specific drugs can lower blood vitamin C concentrations in humans is limited. Dihydropyridine calcium channel blockers e.

However, a reduction in blood vitamin C concentrations with these drugs has not been reported in humans Aspirin can impair vitamin C status if taken frequently Conversely, there are case reports suggesting that supplemental vitamin C may lower blood concentrations of some medications, such as fluphenazine the antipsychotic drug, Prolixin and indinavir the antiretroviral drug, Crixivan There is some evidence, though controversial, that vitamin C interacts with anticoagulant medications like warfarin Coumadin.

Large doses of vitamin C may block the action of warfarin and thus lower its effectiveness. In addition, vitamin C may bind aluminum in the gut and increase the absorption of aluminum-containing compounds e.

People with impaired kidney function may be at risk for aluminum toxicity when supplemental vitamin C is taken at the same time as these compounds , Finally, supplemental vitamin C may increase blood estrogen concentrations in women using oral contraceptives or hormone replacement therapy The potential effect of antioxidants during chemotherapy is not well understood, yet only likely to be an issue if a specific chemotherapeutic agent acts through an oxidative mechanism, which is uncommon It is not clear whether vitamin C given parenterally could diminish or increase the efficacy of chemotherapy drugs — in particular, akylating agents e.

Patients are advised to discuss with their oncologist before using vitamin C supplements , Because high doses of vitamin C have also been found to interfere with the interpretation of certain laboratory tests e.

A three-year randomized controlled trial in patients with documented coronary heart disease and low blood HDL concentrations found that a combination of simvastatin Zocor and niacin increased HDL concentration, inhibited the progression of coronary artery stenosis narrowing , and decreased the frequency of cardiovascular events, such as myocardial infarction and stroke Since the antioxidants were taken together in this trial, the individual contribution of vitamin C cannot be determined.

These contradictory findings indicate that further research is needed on potential interactions between antioxidant supplements and cholesterol -lowering drugs, such as HMG-CoA reductase inhibitors statins. Vitamin C is known to function as a highly effective antioxidant in living organisms. However, in test tube experiments, vitamin C can interact with some free metal ions and lead to the generation of potentially damaging free radicals. Although free metal ions are not generally found under physiological conditions, the idea that high doses of vitamin C might be able to promote oxidative damage in vivo has received a great deal of attention.

Widespread publicity has been given to a few studies suggesting a pro-oxidant effect of vitamin C , , but these studies turned out to be either flawed or of no physiological relevance. A comprehensive review of the literature found no credible scientific evidence that supplemental vitamin C promotes oxidative damage under physiological conditions or in humans Thus, the Linus Pauling Institute recommends a vitamin C intake of mg daily for adults to ensure replete tissue concentrations 29 — an amount substantially higher than the RDA yet with minimal risk of side effects.

This recommendation can be met through food if the diet includes at least several servings of vitamin C-rich fruit and vegetables e. Most multivitamin supplements provide at least 60 mg of vitamin C.

A vitamin C intake of at least mg daily may be particularly important for older adults who are at higher risk for age-related chronic diseases. Pharmacokinetic studies in older adults have not yet been conducted, but there is some evidence suggesting that the efficiency of one of the molecular mechanisms for the cellular uptake of vitamin C declines with age Because maximizing blood concentrations of vitamin C may be important in protecting against oxidative damage to cells and biological molecules, a vitamin C intake of at least mg daily might benefit older adults who are at higher risk for chronic diseases caused, in part, by oxidative damage, such as heart disease, stroke , certain cancers , and cataract.

For more information on the difference between Dr Linus Pauling's recommendation and the Linus Pauling Institute's recommendation for vitamin C intake , select the highlighted text.

Originally written in by: Jane Higdon, Ph. Updated in November by: Jane Higdon, Ph. Updated in September by: Jane Higdon, Ph. Updated in December by: Jane Higdon, Ph. Updated in January by: Jane Higdon, Ph. Updated in September by: Victoria J. Drake, Ph. Updated in November by: Giana Angelo, Ph. Updated in July by: Barbara Delage, Ph. Reviewed in December by: Anitra C. Carr, Ph. Reviewed in December by: Alexander J.

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Int J Geriatr Psychiatry ; 13 : — Sign In. Advanced Search. Search Menu. Article Navigation. Close mobile search navigation Article Navigation. Volume Toward a new recommended dietary allowance for vitamin C based on antioxidant and health effects in humans. Oxford Academic. Balz Frei. E-mail balz. Select Format Select format. Permissions Icon Permissions. Antioxidant , cancer , cardiovascular disease , cataract , DNA , lipid , protein , recommended dietary allowance , vitamin C , adults.

Two major properties of vitamin C make it an ideal antioxidant. These low reduction potentials enable ascorbate and the ascorbyl radical to react with and reduce basically all physiologically relevant radicals and oxidants. The second major property that makes vitamin C such an effective antioxidant is the stability and low reactivity of the ascorbyl radical formed when ascorbate scavenges a reactive oxygen or nitrogen species Eq 1.

The ascorbyl radical readily dismutates to form ascorbate and dehydroascorbic acid Eqs 1 and 2 , or is reduced back to ascorbate by an NADH-dependent semidehydroascorbate reductase 9 , 20 , The 2-electron oxidation product of ascorbate, dehydroascorbic acid, can itself be reduced back to ascorbate by glutathione, the glutathione-dependent enzyme glutathione:dehydroascorbate oxidoreductase [glutathione dehydrogenase ascorbate , or glutaredoxin], or the NADPH-dependent selenoenzyme thioredoxin reductase 9 , 20 , Alternatively, dehydroascorbic acid is rapidly and irreversibly hydrolyzed to 2,3-diketogulonic acid DKG Eq 3 Although substantial scientific evidence exists regarding the antioxidant and health effects of vitamin C in humans, further investigations of the role of vitamin C both in vitro and in vivo are warranted, particularly because vitamin C, being a redox-active compound, can act not only as an antioxidant, but also as a prooxidant in the presence of redox-active transition metal ions Reduction of metal ions such as iron or copper by vitamin C in vitro Eq 4 can result in the formation of highly reactive hydroxyl radicals via reaction of the reduced metal ions with hydrogen peroxide, a process known as Fenton chemistry Eq 5.

Lipid hydroperoxides may also be broken down by the reduced metal ions, resulting in the formation of lipid alkoxyl radicals Eq 6 that can initiate and propagate the chain reactions of lipid peroxidation The mechanism shown in equation 5 , however, requires the availability of free, redox-active metal ions and a low ratio of vitamin C to metal ion, conditions unlikely to occur in vivo under normal circumstances 11 , 15 , Furthermore, it was shown recently that in biological fluids such as plasma, vita-min C acts as an antioxidant toward lipids even in the presence of free, redox-active iron Vitamin C dose.

Plasma change. Open in new tab. Population duration. Endpoint events. Something went wrong on our side, please try again. Show references Vitamin C ascorbic acid. Natural Medicines.

Accessed Dec. Pazirandeh S, et al. Overview of water-soluble vitamins. Vitamin C. Office of Dietary Supplements. Can zinc supplements help treat hidradenitis suppurativa? Vitamin C and mood Eye vitamins: Can they prevent or treat glaucoma?

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