In studies that bolster theories about the link between vitamins and clogged arteries, Harvard University researchers report that people who take massive daily doses of Vitamin E have a significantly reduced risk of heart disease--although they caution that it is still too soon to recommend widespread use of the vitamin.
Separate studies of men and women who took daily Vitamin E supplements of at least 100 international units--more than three times the recommended daily allowance--had a 40% lower risk of heart disease than those who did not, the studies found.
The researchers said that the reduction in risk appeared after two years of taking the supplements and that people who simply consumed a diet rich in Vitamin E did not derive the same health benefit as those who took the supplements. They also found that the benefit did not improve when people took more than 100 units.
The findings, which appear in today's issue of the New England Journal of Medicine, provide important backing for the much-heralded theory that antioxidants--which include vitamins E, C and the nutrient beta carotene--lower cholesterol and thus cut the risk of coronary disease.
So much evidence has now accumulated that it is time for large-scale clinical trials to test this hypothesis, heart experts said Wednesday. If the theory bears out, the result could be a simple, cheap and effective measure that could prevent tens of thousands of heart attacks each year.
"I think we have some very exciting potential here," said Meir Stampfer, the Harvard epidemiologist who served on the study of women and Vitamin E. "If this really proves true, then we could look forward to making a pretty big dent in our leading killer."
Joseph Witztum, a UC San Diego heart expert, said, "This is pretty dramatic. . . . The implications of this are so enormous that, if correct, it could have a major impact on the public health with fairly minimal (cost)."
As co-director of a specialized research unit on atherosclerosis, Witztum has spent 13 years examining the oxidation hypothesis. The theory is based on the notion that cholesterol must undergo oxidation--the same process that causes oils to become rancid when exposed to air--in order to get inside the cells that line the walls of blood vessels.
Once inside the cells, the cholesterol forms plaques that lead to atherosclerosis, in which the arteries are clogged and the passage of blood is hampered. Scientists theorize that if they could find a way to prevent oxidation, they could lower cholesterol and prevent heart disease.
This is where Vitamin E fits in. The vitamin is carried in the bloodstream, primarily in the particles of LDL--low-density lipoprotein--that form so-called bad cholesterol. Vitamin E is thought to prevent the oxidation process, blocking the LDL from infiltrating the cells. "This fits in very nicely with what we observed," Stampfer said.
One heart expert--Dr. Dean Ornish, director of the Preventive Medicine Research Institute at UC San Francisco--chided the Harvard researchers for being too cautious in their reluctance to advocate widespread use of Vitamin E.
"If they had shown a drug did this, I don't think they would put that caution in there," Ornish said. "Given the low toxicity of Vitamin E and the low cost of it, I would recommend people take Vitamin E in this dosage."
But both Ornish and the Harvard researchers agreed that people should not abandon other healthy habits in favor of Vitamin E.
"Vitamin E is not a panacea," said Eric Rimm, the Harvard researcher who headed the men's study. "By no means is Vitamin E suddenly going to replace the fact that people have to worry about smoking and losing weight."
The Harvard findings were drawn from long-running examinations of the dietary habits of 87,245 female nurses from 11 states and 39,910 male health professionals from Boston. The studies--dubbed the Nurses' Health Study and the Health Professionals Follow-Up Study--rely on the subjects' answers to detailed questionnaires about their eating habits.
All the subjects were free of heart disease at the outset of the studies. Researchers have followed the women for eight years and the men for four, drawing links between the subjects' diet and the diseases they have developed over the course of that time.
The study also looked at the effects of Vitamin C and beta carotene. In a finding that contradicted previous studies, the Harvard research showed no relationship between Vitamin C and a reduced risk of heart disease.
But the study did find that beta carotene--a nutrient found in carrots, yellow squash and broccoli--had a beneficial effect on the cardiovascular health of smokers and former smokers. The study found that among men who smoked, those who ingested high levels of beta carotene had 70% less coronary disease than those who did not.
Among former smokers, the study found, men with the highest level of beta carotene intake had a 40% lower risk of heart disease than men with the lowest levels.
The studies are epidemiologic in nature, meaning that they examine patterns but do not demonstrate cause-and-effect relationships. Thus, despite the dramatic findings, the Harvard researchers cannot say for certain that Vitamin E prevents heart disease.
It is possible, for example, that other factors--such as whether the study subjects exercised regularly or ate a healthy diet--affect the findings. But when researchers tested for those "confounding factors," they found little difference in the behavior of those who took the Vitamin E supplements and those who did not.