TORONTO, CANADA. A folic acid deficiency has been linked to an increased risk of giving birth to a baby with neural tube defects (NTDs), or spina bifida. In 1998 Canada, the US, and Chile passed a law mandating that all flour and uncooked cereal-grain products be fortified with folic acid (140 micrograms/100 grams). Since 1998 the number of babies born with NTDs has decreased by anywhere from 15-50% in the US, Canada, and Chile. Clearly, a superb example of the benefits of active cooperation between science and public health policy - or maybe not?

Dr. Young-In Kim of the University of Toronto now suggests that, while folic acid fortification has been an unqualified success in reducing NTDs, it may have created other problems. In other words, what is good for a relatively small proportion of the overall population (pregnant women) may be detrimental to a much larger part of the population. Dr. Kim points out that, while folic acid is effective in preventing the initiation of many forms of cancer, it may actually accelerate the growth of already existing cancers. Folate plays a very important role in DNA synthesis and replication, which is great when it comes to healthy cells, but not when it comes to cancerous cells. Rapid replication and proliferation is the last thing you want in the case of cancer cells. As a matter of fact, experiments have shown that inducing a folate deficiency inhibits tumour growth and at least two chemotherapy agents (methotrexate and 5-fluorouracil) owe their effect to the fact that they counteract the cell proliferation effect of folic acid.

Dr. Kim concludes that, "The potential cancer-promoting effect of folic acid fortification in the vast majority of the US population, who are not at risk of NTDs, but have unintentionally been exposed to high amounts of folic acid, is a legitimate public health concern and needs careful monitoring".
Kim, YI. Will mandatory folic acid fortification prevent or promote cancer? American Journal of Clinical Nutrition, Vol. 80, November 2004, pp. 1123-28

Editor's comment: There is substantial evidence that a folic acid deficiency is implicated in Alzheimer's disease, atherosclerosis, heart attack, stroke, osteoporosis, colon cancer, depression, dementia, hearing loss, and of course, NTDs. Thus it is clearly vital to ensure an adequate daily intake of this important nutrient. The generally recommended intake is 400-600 micrograms/day. With the advent of general fortification it has become more difficult to know exactly how much one is consuming and the risk of overdosing is certainly very real. While this is probably not a major problem for healthy people, it could well be for those with established or not yet diagnosed cancer. So the safest approach is to limit one's supplemental folic acid intake to 400 micrograms/day - the amount found in most multivitamins. Folic acid should always be taken together with vitamin-B6 and vitamin-B12.