ABSTRACT This review provides information determining how much vitamin C to take, including analysis of the recent findings, which demonstrate advantages and problems with higher daily doses. The Daily Value for vitamin C was raised to 90 mg for men in 2000, and Upper Limit of 2,000 mg per day was established as being safe. This followed a study of urinary excretion of vitamin C (AA) that demonstrated 500 mg twice a day provides levels sufficient to cause continuous urinary excretion in humans. That is the lowest oral dosage evaluated that significantly saturates blood plasma. A later study endorsed 200 mg from dietary sources for the RDA. Even though plasma concentration of AA is then significantly lower, at 200 mg daily certain white blood cells are saturated with AA. Recently many studies have indicated the benefit of high levels of AA to maintain the brain, bones, and heart, reduce damage from stroke, brain trauma, and cataracts, and lower the risk of cancer metastasis and colds. Pro-oxidant activity has been found only for i.v. adminstration, where high concentrations appear effective destroying tumor cells while not harming normal cells. This review evaluates recent research and finds it consistent with the hypothesis that people, especially older people and soldiers in combat environments, are likely to benefit if they maintain the saturating level of AA by taking 500mg supplements twice a day.
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