Vitamin C requirements have been controversial ever since Linus Pauling espoused megadoses of the vitamin to prevent various types of diseases, especially the common cold, about 30 years ago. Pauling’s claims attracted attention because he won the coveted Nobel Prize in both the chemistry and peace categories.
Based on extrapolation from animal production of vitamin C (most animals are able to synthesize vitamin C in their livers from glucose; humans lack the enzyme to do so), Pauling felt that humans needed 2,000 to 4,000 milligrams of vitamin C a day under normal conditions, with higher levels during increased stress events. Pauling himself took a whopping 18,000 milligrams daily. Shortly before he died in 1994 of prostate cancer at age 93, Pauling expressed the opinion that his massive vitamin C ingestion probably extended his life.
Vitamin C, or ascorbic acid, is the primary antioxidant found in the watery portion of the blood. It works with other nutrient antioxidants, such as vitamin E and the trace mineral selenium, to neutralize the effects of free radicals, dangerous unpaired electrons constantly produced during oxygen metabolism. If they’re not neutralized, free radicals attack fatty structures in cell membranes and cellular nucleic acids, which can result in such problems as accelerated aging and cancer.
While the United States government decrees that 60 milligrams of vitamin C is sufficient to cover the needs of most people, many scientists, like Pauling, believe that’s insufficient. More recent studies show that an optimal intake of vitamin C begins at the 200-milligram-a-day mark. Since vitamin C is water-soluble, excess amounts are rapidly excreted by the body.
The question is, What’s the true optimal level of vitamin C intake for maximizing antioxidant protection? In an effort to figure that out, scientists from Arizona State University East provided graded doses of vitamin C, from 75 to 2,000 milligrams daily, to 10 healthy, nonsmoking college students.1 During the 10-week study they limited their fruit and vegetable intake to fewer than three servings a day, since those foods are the richest sources of vitamin C. They also took a daily vitamin-and-mineral supplement. Starting at the third week of the study, the subjects began taking either a vitamin C capsule or a placebo, identical in appearance and taste.
The dose of the vitamin C increased every two weeks, from 250 milligrams to 2,000 milligrams by the end of the 10 weeks. The authors took fasting blood samples from the subjects every two weeks and analyzed them for markers of oxidation. By the end of the study plasma levels of vitamin C in those getting the genuine supplement rose 55 percent, while measures of oxidative stress decreased 60 to 90 percent. Significant markers of oxidative stress dropped during intakes of 500, 1,000 and 2,000 milligrams of vitamin C. Since there wasn’t any difference in oxidative stress markers between the 1,000- and 2,000-milligram vitamin C dosages, the authors concluded that maximal antioxidant protection offered by vitamin C occurs in the 500-to-1,000-milligram-dose range. Since other studies show that vitamin C lasts about 12 hours in the blood, it’s best to take the vitamin at least twice daily.
1 Johnston, C.S., et al. (2001). Plasma-saturating intakes of vitamin C confer maximal antioxidant protection to plasma. J Amer College Nutr. 20:623.