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If you take vitamin B supplements to guard against heart disease you are wasting your money, research published in today's issue of the Journal of the American Medical Association suggests.

A clinical trial involving 3,096 patients with established heart disease revealed the vitamins were ineffective against heart attack, death from heart disease and stroke.

The notion that B vitamins ward off heart disease stems from the fact that three B vitamins - folic acid, B6 and B12 - lower blood homocysteine, an amino acid made by the body during normal metabolism. High homocysteine is thought to damage the lining of the arteries. Studies have demonstrated the ability of homocysteine to cause oxidative stress and inflammation, as well as to impair blood clotting and blood vessel function.

The level of homocysteine in your bloodstream is influenced by diet and genetics. Folic acid, B6 and B12 break down homocysteine and prevent it from accumulating in the bloodstream. Numerous studies have shown that taking folic acid supplements, either alone or in combination with B6 and B12, lowers homocysteine levels.

In today's study, researchers from Norway set out to determine whether lowering homocysteine could prevent further heart attacks and heart problems in people with coronary heart disease. Patients were assigned to receive a daily supplement of either folic acid plus vitamins B6 and B12; folic acid plus vitamin B12; vitamin B6 alone; or a placebo. The doses of vitamins used were 0.8 milligrams of folic acid, 0.4 milligrams of B12 and 40 milligrams of B6.

Patients were monitored to determine the rates of all-cause death, stroke, heart attack and hospitalization for unstable angina among the four groups. (Unstable angina is severe chest pain that occurs when the heart becomes starved for oxygen.) After three years of follow-up, none of the B vitamin combinations lowered the risk of heart attack, stroke or death despite an overall 30-per-cent reduction in blood homocysteine levels.

This isn't the first time the value of B vitamins for preventing or delaying heart problems has been challenged.

Earlier this year, the women's antioxidant and folic acid cardiovascular study, a randomized controlled trial involving 5,442 women at high risk for heart disease, found that B vitamins did not lower the risk of cardiovascular events (such as heart attack, stroke and coronary artery bypass surgery) even though the women's homocysteine levels dropped significantly.

The findings suggest that lowering homocysteine does not change the course of heart disease. Instead, elevated homocysteine may signal an increased risk of problems in people who already have heart disease. The effect of long-term folic acid supplementation on the risk of heart disease in healthy people is unknown.

It is possible, however, that B vitamins help prevent stroke. In the study, there was a lower risk of suffering a stroke among B vitamin users, but this finding was not statistically significant, which means it could have been a chance finding.

There is other evidence that folic acid guards against stroke. The mandatory addition of folic acid to certain foods (white flour, enriched pasta, enriched corn meal), implemented in Canada and the United States in 1998, has been linked with a pronounced decline in death from stroke in both countries.

Fortification of food with folic acid was introduced to reduce the risk of neural tube birth defects in infants (when the brain and spinal cord fail to close properly during the early weeks of pregnancy.) Since it began, the rate of these defects has dropped 46 per cent in Canada.

There are concerns that large doses of folic acid could do more harm than good.

Last year, a trial of 1,021 men and women who had had precancerous polyps removed from the colon found that those who took a folic acid supplement (one milligram) got just as many new polyps as those who took placebo pills. People in the folic acid group also had higher rates of advanced tumours, although this finding was not statistically significant.

In today's study, the risk of cancer was slightly higher in the group receiving folic acid, but again it was not statistically significant.

Together, these findings raise the possibility folic acid may prevent early stages of cancer but could enhance the growth of established cancer cells. For this reason, if you have a history of colon cancer, or precancerous colon polyps, avoid taking high-dose folic acid supplements.

While there's little evidence to warrant taking folic acid to protect from heart disease, it is important to increase your intake of folate from foods to help meet your recommended daily intake. (Folate refers to the B vitamin found naturally in foods; folic acid is the synthetic version added to vitamin pills and fortified foods.).

Folate is needed to make DNA and red blood cells, support cell division and growth, and prevent neural tube defects. Women of childbearing age should take a multivitamin with folic acid.

Adults and teenagers need 400 micrograms (0.4 mg) of folate each day. The recommended intake for children aged 1 to 3 is 150 micrograms; from 4 to 8 years, 200 micrograms; and 9 to 13 years, 300 micrograms. Good food sources include legumes, Brussels sprouts, cooked spinach, asparagus, artichokes, avocados, orange juice and enriched pasta.

The safe upper limit for supplemental folic acid is 1,000 micrograms (one milligram) a day, unless directed otherwise by your physician. Taking high doses of folic acid can sometimes mask the presence of a vitamin B12 deficiency. If this condition isn't properly diagnosed, it may lead to irreversible nerve damage.

Leslie Beck, a Toronto-based

dietitian at the Medcan Clinic,

is on CTV's Canada AM every Wednesday. Her website is

lesliebeck.com.

FINDING FOLATE IN FOODS

SOURCE: CANADIAN NUTRIENT FILE, V 2008