BETHESDA, Md--Although only 10 mg/day of vitamin C is enough to prevent deficiency, the optimal daily intake is probably 200 mg, according to results of a new NIH-sponsored study. The current Recommended Dietary Allowance (RDA) is 60 mg.
In this study, vitamin C was given in various amounts to seven healthy young male volunteers who lived in a hospital ward for the duration of the study so that intake could be strictly controlled. The NIH researchers, led by Dr. Mark Levine, found that the 200 mg level was best absorbed by the body; absorption levels fell as the dose was raised above 200 mg.
Daily doses higher than 400 mg offer no additional value, Dr. Levine said, since, at that level, a large amount of the dose is excreted from the body. The research also suggests that very high doses could be dangerous: At 1,000 mg/day, the urine was found to contain oxalate, a breakdown product of the vitamin that could lead to kidney stone formation in some people.