Tolerable Upper Intake Level (UL): Maximum daily intake unlikely to cause adverse health effects.Estimated Average Requirement (EAR): Average daily level of intake estimated to meet the requirements of 50% of healthy individuals usually used to assess the nutrient intakes of groups of people and to plan nutritionally adequate diets for them can also be used to assess the nutrient intakes of individuals.Adequate Intake (AI): Intake at this level is assumed to ensure nutritional adequacy established when evidence is insufficient to develop an RDA.Recommended Dietary Allowance (RDA): Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals often used to plan nutritionally adequate diets for individuals.These values, which vary by age and gender, include the following: DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. Intake recommendations for vitamin C and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine (IOM) of the National Academies (formerly National Academy of Sciences). Relatively low levels of vitamin C (micromolar concentrations) are found in extracellular fluids, such as plasma, red blood cells, and saliva. High levels of vitamin C (millimolar concentrations) are maintained in cells and tissues and are highest in leukocytes (white blood cells), eyes, adrenal glands, pituitary gland, and brain. The total body content of vitamin C ranges from 300 mg (at near scurvy) to about 2 g. Pharmacokinetic modeling predicts that even doses as high as 3 g ascorbic acid taken every 4 hours would produce peak plasma concentrations of only 220 micromol/L. Results from pharmacokinetic studies indicate that oral doses of 1.25 g/day ascorbic acid produce mean peak plasma vitamin C concentrations of 135 micromol/L, which are about two times higher than those produced by consuming 200–300 mg/day ascorbic acid from vitamin C-rich foods. However, at doses above 1 g/day, absorption falls to less than 50% and absorbed, unmetabolized ascorbic acid is excreted in the urine. Approximately 70%–90% of vitamin C is absorbed at moderate intakes of 30–180 mg/day. Oral vitamin C produces tissue and plasma concentrations that the body tightly controls. The physiologic importance of dehydroascorbic acid uptake and its contribution to overall vitamin C economy are unknown. In vitro studies have found that oxidized vitamin C, or dehydroascorbic acid, enters cells via some facilitated glucose transporters and is then reduced internally to ascorbic acid. Cells accumulate vitamin C via a second specific transport protein. The intestinal absorption of vitamin C is regulated by at least one specific dose-dependent, active transporter. Insufficient vitamin C intake causes scurvy, which is characterized by fatigue or lassitude, widespread connective tissue weakness, and capillary fragility. In addition to its biosynthetic and antioxidant functions, vitamin C plays an important role in immune function and improves the absorption of nonheme iron, the form of iron present in plant-based foods. Ongoing research is examining whether vitamin C, by limiting the damaging effects of free radicals through its antioxidant activity, might help prevent or delay the development of certain cancers, cardiovascular disease, and other diseases in which oxidative stress plays a causal role. Vitamin C is also an important physiological antioxidant and has been shown to regenerate other antioxidants within the body, including alpha-tocopherol (vitamin E). Collagen is an essential component of connective tissue, which plays a vital role in wound healing. Vitamin C is required for the biosynthesis of collagen, L-carnitine, and certain neurotransmitters vitamin C is also involved in protein metabolism. Humans, unlike most animals, are unable to synthesize vitamin C endogenously, so it is an essential dietary component. Vitamin C, also known as L-ascorbic acid, is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement. For a general overview, see our consumer fact sheet.įor information on vitamin C and COVID-19, see Dietary Supplements in the Time of COVID-19. This is a fact sheet intended for health professionals.
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