If you take a daily supplement of B vitamins in the hopes of warding off a heart attack, a new study confirms what previous findings have already suggested: You're wasting your money.
In a review of eight trials involving 24,210 people, not one study supported the notion that taking B vitamins prevents heart disease. When analyzed together, the data showed that B vitamin pills were no better than placebos at guarding against heart attack, stroke or death from heart disease.
The new study was led by Venezuelan researcher Arturo Marti-Carvajal of the Cochrane Network, an international body that performs systematic reviews of medical research.
The idea that B vitamins - in particular folic acid, B6 and B12 - protect from heart disease has to do with homocysteine, an amino acid found normally in the blood. When elevated, however, homocysteine is thought to increase the risk of heart attack and stroke.
Excess homocysteine impairs flow through blood vessels and makes it easier for blood-clotting cells to clump together, which can lead to a heart attack.
Folic acid, B6 and B12 are needed to breakdown homocysteine and prevent it from building up in the bloodstream.
If your diet lacks these B vitamins, your homocysteine level can rise. One study found that consuming too little folate increased the risk of cardiac events.
Folic acid, added to vitamin supplements and fortified foods, is the synthetic version of the B vitamin folate.
Folate occurs naturally in such foods as leafy greens, asparagus, legumes, avocado and citrus fruit.
Researchers have also demonstrated that supplementing with B vitamins, especially folic acid, lowers elevated blood homocysteine.
Even so, there's no evidence that bringing down homocysteine prevents a future heart attack or stroke. In fact, previous studies have found B vitamin supplements ineffective for preventing heart attack, stroke or cardiac bypass surgery in people with existing heart disease or those at high risk for developing it.
The current analysis of eight homocysteine-lowering trials concluded there's no justification for taking B vitamins to keep your heart healthy.
It's unclear why B vitamins haven't helped. It's possible that since mandatory folic acid food fortification - introduced in 1998 to reduce birth defects - B vitamin supplements have a lesser effect on homocysteine levels than expected. (In Canada, white flour, enriched pasta and enriched cornmeal are fortified with folic acid.) Or B vitamins may have no effect on the course of heart disease.
Trials have been conducted in individuals at high risk for suffering a cardiac event. The effect of taking folic acid on risk of heart disease in healthy people is unknown.
There's another reason to consider pitching your folic acid supplement. Recent evidence suggests that getting too much folic acid may increase the risk of cancer in predisposed individuals, especially colon cancer.
Folate is needed for the formation and repair of DNA, the genetic material of cells, and there's some evidence that a deficiency of folate can damage DNA that may lead to cancer.
Several studies have linked a low folate diet to an increased risk of cancers of the colon, breast and pancreas.
However, folate's cancer connection is complicated. It may help prevent certain cancers in some people, but speed them up in others.
What sets people apart is their cancer status at the time they start taking supplements.
If they are cancer free, then supplements could help keep some cancers at bay. But if they already harbour some microscope cancerous or precancerous cells, then additional folate could make them multiply faster.
For this reason, anyone over 50 and at increased likelihood of having an undetected cancer, should talk to a doctor before taking folic acid. I advise my clients to stick with a multivitamin that supplies no more than 0.4 milligrams of the vitamin, the recommended daily intake.
Not everyone should stop taking folic acid, however. Women of child-bearing age are urged to take a daily multivitamin providing 0.4 to one milligram of folic acid. Folic acid is needed for cell division before and during the early weeks of pregnancy and is vital to preventing neural tube defects (NTDs), serious birth defects of the brain and spinal cord.
Women at high risk for NTDs - those with epilepsy, Type 1 diabetes, a family history of NTDs and those who are obese - are advised to take five milligrams a day of folic acid a few months prior to pregnancy and continue until 12 weeks into pregnancy.
While some people may benefit from a B vitamin supplement - be it folic acid, B12 or B6 - most of us will get what we need to stay healthy from a varied and well-balanced diet.
Leslie Beck, a Toronto-based dietitian at the Medcan Clinic, is on CTV's Canada AM every Wednesday. Her website is lesliebeck.com.