Is high-dose vitamin C risky?

By Bill Sardi
Knowledge of Health, Inc.
Copyright 2000

Recently the National Academy of Sciences (NAS) issued dietary antioxidant recommendations. The new recommendations call for 90 mg. for vitamin C for healthy adults, up from 60 mg per day under the previous standard. Yet government health authorities keep preaching five servings of fresh fruits and vegetables, which supplies more than 200 mg. of vitamin C. [Am J Clin Nut 62: 1347-56S, 1995] These two figures don't correlate.

Just months before the 90 mg vitamin C recommendation was issued, various government scientists were calling for 120-200 mg per day in published reports. [Proc Natl Acad Sci 93: 3704-09, 1996; Nutrition Reviews 57: 222-24, 1999; Am J Clin Nut 69: 1086-1107, 1999] One researcher at the Massachusetts Institute of Technology, Laboratory of Human Nutrition, using a technique called saturation kinetics, suggested that even the 200-mg level was not adequate to meet individual vitamin C needs by as much as 2-3 fold. [Proc Natl Acad Sci 93: 14344,48, 1996]

While the Food & Nutrition Board suggested adding another 35 mg of vitamin C for smokers (125 mg total), researchers at the Medical College of Wisconsin found that it takes 200 mg of vitamin C before smokers achieve the same serum levels of ascorbic acid as non-smokers. [Am J Clin Nut 53: 1466-70, 1991] Other investigators have called for 200-mg daily consumption of vitamin C for smokers. [Ann NY Acad Sci 686: 335-46, 1993] Swedish investigators demonstrated that a single 2000 mg dose of vitamin C can completely abolish the typical reduction in blood circulation that occurs while smoking a cigarette. A 1000 mg dose had no effect. [Microvascular Res 58: 305-11, 1999]

What happened to these recommendations? The NAS recommendations conveniently stopped short of recommending levels of vitamin C that would require supplementation. The Academy of Sciences set the tolerable upper limit at 2000 mg, but a recent review indicated doses of vitamin C up to 4000 mg. are well tolerated. [Nut Rev 57: 71-77, 1999] Eight placebo-controlled, double-blind studies and six non-placebo clinical trials in which up to 10,000 mg of vitamin C was consumed daily for up to 3 years confirm the safety of vitamin C in high doses. [J Am Coll Nut 14: 124-36, 1995] Yet the headline in the press release from the National Academy of Sciences concerning antioxidants read "huge doses considered risky."

Furthermore, Maret Traber PhD, a member of the NAS panel, says there is "no evidence that proves antioxidant supplements will help people live better longer." [Whole Foods Magazine, August 2000] Really? There was a UCLA study, which showed that greater than 300 mg of daily vitamin C increases the male life span by six years, a report that was widely reported in Newsweek and other periodicals. [Epidemiology 3: 194-202, 1992] A recent study confirms that finding. [Epidemiology 11: 440-45, 2000]

Furthermore, one study shows that about 294 mg of vitamin C significantly decreases the risk of cataracts compared to 77 mg. per day (about the level set by the Academy of Sciences). [Clin Chem 39: 1305, 1993] To get that much vitamin C a person would have to consume 5 oranges per day. Daily consumption of vitamin C supplements for 10 years or more results in a 77-83 percent reduction in the prevalence of cataracts. [Am J Clin Nut 66: 911-16, 1997]

One of the fallacies of current vitamin C research is the use of blood serum levels as the gold standard for establishing recommended daily consumption levels. A 1991 study, conducted at the USDA Human Nutrition Research Center on Aging at Tufts University, found that there were "striking differences" in ocular levels of vitamin C among older adults who consume 148 mg of vitamin C from their daily diet (which is 2.5 times the old 60 mg RDA and 1.6 times the current 90 mg recommendation) compared to adults who took 2000 mg daily from supplements. The level of vitamin C in the focusing lens and aqueous fluid of the eye increased by 22-32 percent with consumption of 2000 mg of daily vitamin C supplementation, which affords protection against cataracts. Thus the idea that vitamin C levels reach a saturation point at about 240 mg in the blood serum, and that additional vitamin C is worthless and only washes out in the urine, is dispelled by this research. [Current Eye Research 8: 751-59, 1991] This is the same level of vitamin C that the National Academy of Sciences now considers "risky." [NAS press release April 10, 2000]

The message the National Academy of Sciences sends is always the same, regardless of the evidence, which is that you can get all the nutrients you need from your diet, not pills. But this recommendation comes with asterisks. The fine print reads that the NAS recommendation is only for healthy individuals, and it only spells out "the minimum amount of a nutrient that has beneficial health effects." The NAS says the effects of antioxidants are "promising but unproven."

How much evidence is enough? The answers provided by the NAS Food and Nutrition Board members amount to doublespeak. The discussion becomes almost unintelligible with all the talk about daily value, Recommended Daily Allowance (RDA), USRDA, daily reference intake (DRI) and tolerable upper level. Which consumer, let alone rocket scientist, can decipher these standards so they can make an intelligent health decision?

One assumption is that people don't need antioxidant supplement until they become unhealthy. But the Journal of the American Medical Association admits the destructive process of oxidation is involved in virtually every disease. [J Am Med Assn 271: 1148-49, 1994] Aging, disease and antioxidant status often parallel each other. Living tissues slowly age or wear out, they don't become ill overnight. For example, the focusing lens of the human eye loses about 1 percent of its clarity for every year of life. Cataract formation is universal and slowly progressive with advancing age. By age 60 only about 35 percent of light reaches the retina. By age 85 a person needs a 250-watt light bulb to see what they saw with a 60-watt light bulb when they were 20 years old. The level of vitamin C in the lens of the eye has been correlated with severity of cataract. [Internatl J Vitamin Nutr Res 68: 309-15, 1998] If an individual consumes the minimum amount of vitamin C that produces healthful benefits (90 mg. per day by the NAS standards), and waits till they develop a cataract to take more vitamin C, it will probably be too late to reverse a cataract. About 300-2000 mg per day of vitamin C would be required to prevent cataracts, according to the data at hand.

NAS panel member Maret Traber, Ph.D., says "it was disappointing that the news media focused on the 'new' upper limits for vitamin C, vitamin E and selenium, rather than the 'new requirements'." But it was the NAS themselves who chose to issue a press release that carried the headline "Antioxidants' role in chronic disease prevention still uncertain; huge doses considered risky." Their own press release didn't emphasize the fact that their report called for an increase in the daily intake of vitamins C and E. The NAS can't entirely shift the blame onto the news media. While these experts admit that the news media mistakenly emphasized the tolerable-upper limits issued by the NAS panel of experts, the panel members apparently did nothing to correct the problem either. They could have written to the news media. Apparently none did. ####


Recently the National Academy of Sciences published its "tolerable uppler limits" for vitamin C. The following report was my response. You have permission to post this article, with proper notation of its authorship and my copyright (used with permission) on your website. Vitamin C Foundation