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TUESDAY, June 22 (HealthDay News) -- A new study by British researchers provides the most conclusive evidence to date that taking vitamins to reduce levels of the blood protein known as homocysteine doesn't lower the risk of heart problems.
Homocysteine has been a buzzword among heart disease experts since the early 1990s when scientists noticed that people with elevated levels had an increased risk of heart disease. Because folic acid and other B vitamins are known to lower homocysteine, researchers theorized that taking a daily supplement might lead to heart-related benefits.
The study of more than 12,000 heart attack survivors showed that taking a daily folic acid and vitamin B12 supplement for nearly seven years lowered homocysteine levels by an average of 28%, but failed to reduce the risk of heart attack, coronary death or stroke. Seven previous large-scale trials that looked at whether lowering homocysteine levels with folic acid-based supplements might yield heart benefits came to similar conclusions.
"These results have been combined into a meta-analysis with the other large trials and, collectively, the results are conclusively negative," said Dr. Jane M. Armitage, professor of clinical trials and epidemiology at the University of Oxford and a principal author of the report, published in the June 23/30 issue of the Journal of the American Medical Association.
"Our findings suggest that some other factor is associated with both higher homocysteine levels and with increased risk of heart attacks and strokes," Armitage added. "One possibility is that both these things are associated with impaired kidney function."
For their study, Armitage and her co-authors recruited 12,064 heart attack survivors in the United Kingdom between 1998 and 2008. Roughly half of the patients took a tablet containing 2 milligrams (mg) of folic acid and 1 mg of vitamin B12 daily, while the other half took placebos. During 6.7 years of follow-up, there was no difference in the rate of heart attacks, strokes or coronary death between the two groups.
Some previous studies have raised concerns that large doses of folic acid might increase the risk of certain cancers, but the Oxford study found no increased risk of any form of cancer. A planned collaborative meta-analysis of all the large folic acid supplementation trials "should be able to provide even more reliable evidence about any effects on site-specific cancer," the study authors wrote.
"These results highlight the importance of focusing on drug treatments (e.g., aspirin, statins and antihypertensive therapy) and lifestyle changes (in particular, stopping smoking and avoiding excessive weight gain) that are of proven benefit," the researchers concluded.
That viewpoint is in line with what most U.S. doctors have increasingly come to believe, American experts said.
"The findings can really be seen as putting the idea firmly to rest that lowering homocysteine itself can be beneficial," said Dr. Ronald M. Krauss, a senior scientist at Children's Hospital Oakland Research Institute in Oakland, Calif.
Krauss added that the study illustrates that even if a substance is associated with the risk of disease, "you can't automatically assume that changing the levels of that substance is going to have the expected effect on risk."
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