Vitamin C: Overview and Update

Abstract

Vitamin C functions in enzyme activation, oxidative stress reduction, and immune function. There is considerable evidence that vitamin C protects against respiratory tract infections and reduces risk for cardiovascular disease and some cancers. Current trials are examining the efficacy of intravenous vitamin C as cancer therapy. Many experts believe that the recommended intakes for vitamin C (45 to 90 mg daily) are several orders of magnitude too low to support optimal vitamin C functionality. Also, there is a misperception that vitamin C deficiency disease (scurvy) is largely historical and rarely observed in developed nations. Physical symptoms of scurvy include swelling of the lower extremities, bleeding gums, fatigue, and hemorrhaging, as well as psychological problems, including depression, hysteria, and social introversion. The long-term safety of vitamin C supplementation seems evident as large investigations have noted reduced risk of mortality in vitamin C supplementing populations and in those with elevated plasma vitamin C concentrations.

Vitamin C: is it time to re-evaluate its role in health and disease?

“…Low levels of AA in tissues and cells have been associated with anaemia, gingival bleeding, capillary haemorrhages, poor wound healing, atherosclerotic plaques, muscle degeneration or neurological disturbances [1,3,4]. Vitamin C deficiency lowers resistance to infections, inhibits the immune system, increases the risk of allergic sensitisation and negatively influences the clinical course of many chronic diseases [2][3][4]6].…”

“…Hence to maintain AA pool in the body, humans require VC in their diet. Citrus fruits, strawberries, raspberries, blueberries, cranberries, kiwi, mango, grapefruit, tomatoes, broccoli, Brussels sprouts, spinach, red and green peppers and other leafy vegetables (Table 1) are the major food sources of VC [3,4]. Human diet normally contains its two forms.…”

“…Hence, to achieve the maximal gastrointestinal absorption, several doses smaller than 1000 mg, spaced throughout the day, are better than a single large dose [13,16]. Vitamin C absorbed in the digestive tract circuits mainly as unbound AA and is available as an anti-oxidant in the blood and interstitial fluids [3]. Intracellularly it is reversibly oxidized to an ascorbic radical (semidehydroascorbic acid -SDA) which donates the second electron converting into dehydroacorbic acid or dismutates into ascorbate and DHA [17][18][19].…”

“…A higher intake may trigger mild nausea, vomiting or osmotic diarrhoea. They are however easily reversed within a week or two of reduced intake [2,3,35,36]. Chronic administration of large doses of VC may also adversely affect body iron reserve in hereditary hemochromatosis.…”

“…Unfortunately, up to the beginning of the twentieth century there was no scientific proof that scurvy resulted from the lack of a specific nutrient and that it could be prevented or cured by appropriate dietary manipulation [1][2][3]. In 1928, Hungarian biochemist and Nobel Prize winner Albert Szent-Gyorgyi isolated and structurally characterised hexuronic acid.…”