CORVALLIS, Ore. - A study reported nationally last week that suggested vitamin C supplements may actually increase clogging of the arteries is contrary to a wealth of other research on this topic and may erroneously lead people to believe this valuable antioxidant is a health risk, one expert says.
The research, which was discussed at a meeting of the American Heart Association, reportedly concluded that people who took 500 milligrams a day of vitamin C for at least a year had a rate of thickening of the carotid artery 2.5 times greater than subjects who did not take supplements.
But many studies in recent years have suggested that moderate supplements of vitamin C may have significant value in lowering the risk of heart attacks and strokes, said Balz Frei, professor and director of the Linus Pauling Institute at Oregon State University.
Frei is an internationally recognized expert on the role of antioxidants in heart disease prevention, the author of more than 100 publications in this field and a recipient of several grants from the National Institutes of Health to study the role of vitamin C in heart disease. He also acts as a consultant to a federal panel that is considering raising the recommended daily allowances of antioxidant vitamins.
"The results from the study presented last week, in fact, are in direct conflict with a study published in 1995 in the American Heart Association journal Circulation," Frei said. "That research found a significant reduction in carotid artery wall thickness in people over 55 who consumed about 1,000 milligrams or more of vitamin C a day, compared to those consuming less than 88 milligrams per day."
Frei said the report last week, which had not yet undergone peer review or been published in the scientific literature, did not put its findings in the proper context of hundreds of existing studies demonstrating the health benefits of vitamin C.
"This report will cause unnecessary and unjustified confusion and fear among the public," Frei said.
The implication of the study reported last week, Frei said, is that people who take vitamin C supplements would die of heart attacks and strokes at a much greater rate than those who don't take supplements. But there's no scientific evidence supporting that notion, he said.
To the contrary, many epidemiological studies and some clinical trials have indicated that dietary intake of, or supplementation with vitamin C is associated with a reduction in the incidence of chronic disease and mortality, including cardiovascular diseases.
Findings from other studies, Frei said, include:
- A large epidemiological study published in 1992 showed a risk reduction for heart disease of 45 percent in men and 25 percent in women consuming about 300 milligrams of vitamin C daily from their diet and supplements.
- Not a single epidemiological study or clinical trial has ever found a significantly increased risk of heart attack or stroke in people who take regular vitamin C supplements.
- More than 20 clinical studies since 1996, published primarily in Circulation, have consistently found beneficial effects of vitamin C on the relaxation of arteries, or vasodilation, which is an important risk factor for heart attacks and strokes.
- Published research has found that vasodilation in patients with heart disease is significantly improved following supplementation with 500 milligrams of vitamin C a day, and is comparable to the vasodilation found in healthy people.
- Beneficial effects of vitamin C supplements leading to normalization of vasodilation have also been observed in patients with angina, heart failure, high cholesterol levels, hypertension, diabetes and smokers.
- A recent double-blind, placebo-controlled clinical study published in Lancet demonstrated that 500 milligrams of vitamin C per day lowered blood pressure in moderately hypertensive patients.
Frei said there are several concerns about the study reported last week that raised questions about vitamin C causing atherosclerosis.
It was not yet reviewed and published, he said, and was based on epidemiological observations that do not and cannot prove a cause-effect relationship - there may have been unobserved differences in diet or lifestyle that better explain the actual results of the study. The measurement of carotid artery wall thickness by ultrasound is technically very difficult and the observable differences are exceedingly small. In the recent research, a mobile unit was used to assess artery wall thickness, and reproducibility and accuracy of the data need to be confirmed before conclusions can be drawn from the study, Frei said.
"The known health benefits of vitamin C far outweigh these alleged, unconfirmed risks," Frei said. "I believe that people taking vitamin C supplements should continue to do so. Vitamin C supplements have been shown to normalize vasodilation and lower blood pressure, two major cardiovascular risk factors. "And there is no scientific evidence that vitamin C supplements increase the risk of heart attacks or strokes," he said.