Value of B vitamins in cutting heart disease risk challenged
Reported April 23, 2010
NEW YORK (Reuters Health) – Two studies released this week reach contradictory conclusions on the value of B vitamins and folic acid (or folate in its naturally occurring form) in reducing the risks of heart disease. What are doctors and their patients to make of this?
“Not much,” says Dr. Steven Woloshin of Dartmouth University’s Institute for Health Policy and Clinical Practice.
“One study is very weak and the conclusions can’t be believed and the other’s results don’t add much for practitioners or their patients,” Woloshin told Reuters Health.
In the first study, Japanese researchers wanted to know if folate and vitamins B6 and B12 in the diet would have any affect on deaths due to heart disease.
Foods that are rich in B vitamins and folate include beans, lentils, potatoes, peanuts, spinach, broccoli, brussel sprouts, and some fruits such as bananas, strawberries, and oranges.
Using data from the large observational Japan Collaborative Cohort Study, Dr. Renzhe Cui and colleagues calculated the nutrients eaten daily by 23,119 men and 35,611 women by analyzing their answers given in food “frequency” questionnaires.
After 14 years of follow-up, 3815 deaths related to heart disease were recorded in the study population of 58,730: 986 from stroke, 424 from coronary heart disease, 318 from heart failure, and 2087 from cardiovascular disease.
In a nutshell, the results suggested that eating a diet high in folate and vitamin B6 was associated with reduced risk of death from heart failure in men and with reduced risk of death from stroke, coronary heart disease, and cardiovascular disease in women.
In the American Heart Association’s journal Stroke, the researchers conclude that greater folate and vitamin B6 in the diet may be useful in preventing cardiovascular disease.
Woloshin questions the validity of such a claim, because of the study’s design. The researchers can’t tell from the data what factors may be responsible for the observed differences, Woloshin said: “There’s nothing to hang your hat on.”
“For instance, women were more likely to smoke if they ate less folate. Maybe they have other less healthy habits and that’s why they are more likely to die of heart failure,” Woloshin said. The data gathered in the observational study doesn’t say.
A randomized controlled trial, such as the study by the other research group, is needed to make such claims, he said.
Researchers at the University of Bergen in Norway looked at data gathered in the Western Norway B Vitamin Intervention Trial, which included 3,090 patients suspected of having coronary artery disease.
Participants had angiograms to look at restricted blood flow in the coronary arteries. Blood was also collected to measure levels of an enzyme, homocysteine. High blood levels of homocysteine have been associated with increased risk of heart disease.
Study subjects were randomly assigned to take one of three supplement formulations of folic acid, B6 and B12, or a placebo. One hundred eighty-three patients, with a total of 309 lesions in their coronary arteries, were included in this study’s analysis. After 10 months, blood was tested, follow-up angiograms were performed and blockages measured again.
Even though homocysteine in the blood was reduced an average of 22 percent in the patients who got a folic acid/B12 supplement, “overall disease progression was not affected,” the researchers found.
Writing in the American Journal of Cardiology, Kjetil Loland and colleagues reported detecting “no statistically significant results from treatment.” Coronary artery disease had progressed unabated, they note. In fact in one subgroup, CAD appeared to progress more rapidly for those getting the supplement.
“It must be noted that this was in a post-hoc analysis of a subgroup of patient. We felt however obliged to report this finding,” Loland told Reuters Health in an email.
Otherwise, “the results support a growing amount of evidence that B-vitamin treatment of cardiovascular disease is ineffective” in patients with established cardiovascular disease,” Loland added.
The results also suggest, Loland said, that high homocysteine levels are not a cause of heart disease and treatments aimed at reducing them won’t reduce the heart disease risk itself.
Loland said that by using two measurements of arterial blockage, he and his colleagues were, for the first time, able to look at “clinically silent disease progression.”
Woloshin believes significant research now has settled the question of whether folic acid and B vitamin supplementation help reduce the risks of heart disease. “It doesn’t,” he said.
SOURCE: Stroke, April, 2010. American Journal of Cardiology, April 2010
