Women who take vitamin C supplements may have a lower risk of developing coronary heart disease than women with low intakes of vitamin C, according to a new study. But researchers are still calling for more trials before making recommendations.
"Based on our data, modest amounts of vitamin C supplements may lower one's risk of coronary heart disease," said Stavroula K. Osganian at The Children's Hospital in Boston in the US. However he carried on to say that the "study cannot provide conclusive evidence for a protective role nor can it exclude the possibility that the association may be due to some other health-seeking characteristic among vitamin C supplement users.".
In addition, while it is biologically plausible that the antioxidant properties of vitamin C could help protect against heart disease, he added that studies have produced conflicting results.
"The inconsistent findings from the available observational studies emphasise the need for further evidence from well-designed, randomised clinical trials to help answer this question prior to public policy recommendations regarding the optimal intake of vitamin C or need for supplements," he said.
The study used information from diet questionnaires filled out in 1980 by approximately 85,000 female nurses along with 16 years of follow-up data on heart disease cases that were collected during the Nurses' Health Study. The results appear in the 16 July 2003 issue of the Journal of the American College of Cardiology.
After adjusting for age, smoking, and a variety of other coronary risk factors, the researchers found vitamin C supplement use was associated with a 28 per cent lower risk of coronary heart disease. However, the researchers note that the women in this study generally had a low risk of heart disease.
The median daily intake of vitamin C in the lowest group was 70 milligrams. By contrast, the median daily intake among women in the highest group was 10 times as much (704 milligrams.) The EC Recommended Daily Allowance of vitamin C for women is 60 milligrams per day - although in the US it is higher at 75mg.
"In terms of our study, our results do not support a role for megadoses of vitamin C to lower the risk of coronary heart disease. It should be noted however, that our study population of women is relatively well-nourished, therefore our results apply to such populations, and our study only examines risk of coronary heart disease. The amount of vitamin C needed to prevent other adverse health outcomes, cancer for example, or the amount needed in undernourished populations or special populations needs to be considered when making such public policy recommendations," said Dr Osganian.
This study did not reveal any statistically significant link between heart disease risk and the amount of vitamin C in diet alone. Dr Osganian noted, however, that there was little difference between the highest and lowest reported intakes of vitamin C from diet alone.
In an editorial in the journal, Balz Frei, director of the Linus Pauling Institute at Oregon State University in Corvallis, Oregon in the US wrote that even well-designed trials may not fully answer questions about whether vitamin supplementation can prevent heart disease.
"What we know with certainty, however, is that a healthy diet and lifestyle lowers the risk of coronary heart disease, and this is what we should advocate to coronary heart disease patients and healthy people alike. An additional multivitamin/multimineral supplement as 'health insurance' also is sensible advice, as a vitamin C supplement may help lower coronary heart disease risk," wrote Dr Frei.
He added that the study by Dr Osganian and his colleagues did appear to indicate that vitamin C itself seems to have a protective effect, rather than simply being a marker of fruit and vegetable intake.