Does folic acid really cause breast cancer?

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It is well known that taking folic acid around the time of pregnancy helps to defend against developmental disorders known as ‘neural tube defects’ (such as spina bifida). However, the wisdom of this established nutritional practice was recently called into question on the publication of a study which appeared to link folic acid supplementation with a substantially increased the risk of breast cancer later in life. Widespread media reporting of this study seemed to leave little doubt that women taking traditional action to help ensure a healthy pregnancy might at the same time be jeopardising their own future health.

However, because the manner in which scientific data is presented to or translated by journalists and reporters does not always tell the full story, I resolved to look at this particular research in some depth. The study in question was a follow-up of research conducted in the 1960s in which the effects of folic acid were assessed in about 3000 pregnant women. Women were treated with either 200 mcg of folic acid, 5000 mcg (5 mg) of folic acid or placebo (dummy pill) each day. About 35 years later the health of these women was reassessed. The results, published in the British Medical Journal, showed that women taking the higher dose of folic acid appeared to be at about twice the risk of dying from breast cancer.

While stark, these statistics do not, however, necessarily prove a definite link between folic acid supplementation and breast cancer. The total number of breast cancer cases in those who had taken 5000 mcg of folic acid a day was just eight. With such a small number of cases, there is a good possibility that the association is due not to some real effect, but chance. In fact, standard analysis revealed that the apparent doubling in risk of breast cancer associated with high dose folic acid supplementation during pregnancy was not statistically significant.

The authors of the BMJ study themselves admit that the apparent link between folic acid and breast cancer might be due to chance. The authors of a commentary accompanying the study went further by stating their belief that chance is, in reality, the ‘most likely explanation for the reported association’. Unfortunately, the scientifically suspect nature of the original study did not seem to temper the resulting media reports. My fear is that folic acid’s recent bad press may erode trust in this nutrient, with the potential that babies may be put at greater risk of disability.

Despite the attention it attracted, it is clear that the BMJ study does not give good reason to lose faith in folic acid. Foods rich in folate to emphasise prior to and during pregnancy include green leafy vegetables, beans and lentils. In addition, I recommend that women continue to take accepted advice to supplement 400 mcg of folic acid each day. Because neural tube defects form early on in pregnancy, supplementation should ideally be started at least a month prior to pregnancy, and continued for the first three months of the pregnancy itself. The evidence still shows that folic acid supplementation around the time of pregnancy still has the capacity to deliver the goods.

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