New Vitamin C Findings May Be Overstated

Washington, D.C., March 2, 2000—Researchers at the University of Southern California (USC) reported today the surprising finding that vitamin C may contribute to atherosclerosis or hardening of the arteries. They say that people who took 500 milligrams (mg) of vitamin C as a dietary supplement had a 2.5 times faster progression of thickening of the carotid artery, over a period of 18 months, compared to people who took no supplement. The language of the USC press release is calculated to cause concern and yet the amount of information provided does not clearly justify that concern.

Dr. Jeffrey Blumberg, Chief of the Antioxidants Research Laboratory at the U.S. Department of Agriculture (USDA) Human Nutrition Research Center on Aging at Tufts University, commented, "This is a preliminary epidemiological study and it is important to put the reported findings in the context of all the available information. This is the first report of any negative effect of vitamin C on the arteries in contrast to the totality of data about vitamin C and health. A number of other studies suggest a positive effect of vitamin C on arterial health and the USC researchers offered no plausible mechanism by which vitamin C could have the adverse effect observed in this study."

Dr. Annette Dickinson, vice president for scientific and regulatory affairs at the Council for Responsible Nutrition (CRN), said that several observations were important, even before peer review and publication of the study.

First, this is an epidemiological (observational) study, not a clinical trial and there could be confounding factors that would explain the differences observed. Second, the study involved 573 people, only 30 percent of whom took vitamin C in amounts ranging from 30 to 1,000 mg. Most of those people at the lower end of that range were likely taking their vitamin C in the form of a multivitamin.Dr. Dickinson noted that no information was provided regarding the number of people taking 500 mg or more, or the variability in the rates of thickening of their artery walls. These factors could greatly affect the significance of the findings. Also, there is no indication in the USC press release regarding the clinical significance of the observed change in the rate of carotid wall thickening.

Dr. Dickinson concluded, "Today's press release on this study uses very strong language that appears calculated to create some fear about vitamin C supplementation, without providing sufficient information to justify that concern. The fact is that the weight of all published scientific evidence suggests that vitamin C is beneficial not only for the heart but also protects against cataracts and some types of cancers."