研究称B族维生素对心脏病患者并无明显益处

    食品伙伴网导读：近日一项新的研究称，每日补充叶酸和维生素B12对心脏病患者的心血管方面没有任何的明显益处。该研究同时称，没有证据表明补充叶酸能增加癌症风险。

    原文报道：Daily supplements of folic acid and vitamin B12 did not show any cardiovascular benefits for heart attack survivors, says a new study.

A daily dose of 2 milligrams of folic acid and 1 milligram of vitamin B12 for about seven years was associated with reductions in levels of the amino acid homocysteine, but this was not linked to any benefits in cardiovascular events, according to findings published in the Journal of the American Medical Association (JAMA).

Epidemiological studies have linked increased blood levels of homocysteine to an increased risk of cardiovascular disease (CVD). It has been suggested that by lowering the levels of homocysteine in the blood with B-vitamins, people could cut the risk of CVD.

"It is unrealistic to expect a vitamin to undo a lifetime of unhealthy behaviours.”
Dr Duffy MacKay, Council for Responsible Nutrition.
However, the potential role of B vitamins in heart health, by reducing levels of the amino acid homocysteine reported to increase the risk of cardiovascular disease, is controversial, with many of the randomised controlled trials focussing on people already suffering from heart disease.

The new study was also in people with established cardiovascular problems. The Study of the Effectiveness of Additional Reductions in Cholesterol and Homocysteine (SEARCH) Collaborative Group recruited over 12,000 heart attack survivors for their randomised trial.

“These results highlight the importance of focusing on drug treatments (eg, aspirin, statins, and antihypertensive therapy) and lifestyle changes (in particular, stopping smoking and avoiding excessive weight gain) that are of proven benefit, rather than lowering homocysteine with folic acid–based vitamin supplements, for the prevention of cardiovascular disease,” concluded the authors, led by Jane Armitage from the University of Oxford.

Putting the cart before the horse

Commenting on the study, Duffy MacKay, ND, vice president, scientific & regulatory affairs, for the dietary supplements trade association, the Council for Responsible Nutrition (CRN), said that the study didn’t answer the question of whether long-term B vitamin supplementation and combined with other healthy lifestyle habits could have helped prevent cardiovascular disease before it occurred at all.

“We may need to re-evaluate expectations when designing studies on nutrients used to treat serious chronic disease because it is unrealistic to expect a vitamin to undo a lifetime of unhealthy behaviours,” said Dr MacKay.

“We should remember that scientific knowledge grows in increments, and not to sacrifice the potential positive relationship between B vitamins and cardiovascular health given the results of one study. The researchers may have gotten too far ahead of themselves by expecting to see successful disease treatment without first understanding if the positive relationship between homocysteine levels and cardiovascular disease is causal,” said Dr. MacKay.

Attention should now focus on whether homocysteine is a valid biomarker for in the pathogenesis of heart disease, he added.

Cancer concerns eased

Despite the null results for heart health, the SEARCH group do report potentially positive news for folic acid with their observation that the supplement was not associated with cancer risk: Some concerns over consumption of high levels of folic acid have surfaced, linking the nutrient to increased risks of colorectal cancer.

“Concerns have been expressed that folic acid may play a role in carcinogenesis, preventing initiation when administered in healthy individuals but potentially promoting tumour growth when administered to individuals with established cancers,” wrote the authors.

“SEARCH did not find that any excess of cancer emerged with prolonged treatment, and continued surveillance of the study participants using UK cancer and mortality registries should allow even longer-term safety of folic acid supplementation to be assessed,” they concluded.

Source: JAMA
2010, Volume 303, Number 24, Pages 2486-2494
“Effects of Homocysteine-Lowering With Folic Acid Plus Vitamin B12 vs Placebo on Mortality and Major Morbidity in Myocardial Infarction Survivors: A Randomized Trial”
Authors: Study of the Effectiveness of Additional Reductions in Cholesterol and Homocysteine (SEARCH) Collaborative Group 

    详情见：http://www.nutraingredients-usa.com/Research/B-vitamins-fail-people-with-sick-hearts-Study