Folic acid, one of the B group vitamins, has several important roles to play in human health. The best known of these is the protection provided against a range of serious birth defects such as spina bifida. Over recent years, however, another significant function has been identified by medical research: high levels of folic acid are linked with lowered risk of heart disease.
Evidence for this connection emerged in the late 1990s as a result of the increased folic acid intake by the general population due to a government-mandated supplementation of flour, rice, cornmeal, and other grain products with a small percentage of folic acid. This increase coincided with a fall in blood levels across the population of an amino acid called homocysteine. Homocysteine is a natural byproduct of metabolism, but it acts as an oxidant and many studies have linked high levels of the compound with a range of heart conditions. Other studies (for example, Am J Clin Nutr 1993; 57:47-53) have demonstrated folic acid’s ability to reduce homocysteine levels in trial subjects.
It is believed that the dietary increase of folic acid due to fortification of grain products has probably saved thousands of lives that would otherwise have been lost to cardiovascular disease. There are many research studies that appear to confirm the general trend suggested by the fortification program:
A study published in the British Medical Journal (2002; 325:1202) found “strong evidence that the association between homocysteine and cardiovascular disease is causal.” The authors stated that supplementing with 0.8mg of folic acid per day “should reduce the risk of ischaemic heart disease by 16%, deep vein thrombosis by 25%, and stroke by 24%.”
Several different studies (for example, Circulation. 2002;105:22-6) have shown that folic acid supplementation can improve the functioning of the inner lining of arteries, giving them more flexibility and thus improving circulation. Most of the studies attribute this effect to the lowering of homocysteine levels.
An epidemiological study, published in January 2005 in the Journal of the American Medical Association, examined both dietary and supplemental intake of folic acid for over 140,000 women. It was found that subjects aged 27 to 44 who consumed at least 1mg of folic acid (or folate) per day had a 46% lower risk of hypertension compared with those who consumed less than 0.2mg per day. Interestingly, the women who obtained all their folate from food showed no lowered risk. This was probably because dietary folate is less bioavailable than the synthetic form, and, in addition, it is difficult to achieve high folate levels from diet alone.
A common feature of much of the research is that, to achieve a significant improvement in heart health, the daily dose of folic acid needs to be higher than that can be obtained from eating naturally folate-rich foods and fortified grain products.
There is still a need for controlled clinical trials to prove a direct causal link between folic acid levels and heart health, but, at this stage, the indirect evidence seems quite convincing. For that reason, daily supplementation with folic acid appears to be a wise precaution.