“The claim published in some media recently, that experts have become critical of the practice of fortifying foods with vitamin B9 (folic acid) as studies have shown that high doses of folic acid could increase the risk of bowel cancer, is unjustified and contradicts reality.
The fact is, studies with animals have merely shown that where there is prior evidence of cancer in its preliminary stages (so-called pre-malignant lesions), folic acid can increase the risk of cancer and accelerate tumor growth if taken in very large quantities – much larger than normal requirements (1). No such effects have been observed in humans up to now. They would only be conceivable after large doses for therapeutic purposes, if at all. Although folic acid has been used to treat anemia, epilepsy and other conditions for over 60 years at doses ranging from 5 to 15 mg even over long periods, there have never been reports of any increased risk of bowel cancer in humans.
The crucial point is that folate deficiency increases the risk of cancer in general, and an optimal intake of folate reduces the risk of cancer. Therefore, the present data do not provide grounds for undermining the preventive strategies aimed at improving folic acid provision and public health that have just been successfully initiated.
Since pregnancy is a particularly critical phase for an adequate intake of folate, for the past 15 years women planning a pregnancy have been advised to take supplemental folic acid (400 μg/day) well before conceiving in order to minimize the risk of birth defects (e.g., neural tube defects). Although this recommendation has been made by several professional organizations, only around 10% of women planning a pregnancy actually take folic acid supplements at the right time (at the latest 4 weeks before the start of pregnancy). Moreover, many pregnancies are unplanned. For this reason, it is desirable to improve overall folate intake.
Hence in the United States and Canada, fortification of staple foods (flour) has been mandatory since Jan. 1, 1998, in order to ensure that each citizen consumes approximately 200 μg of folic acid per day in addition to the usual intake of folate in the diet. This measure has proved beneficial over the years and has not only led to a marked decrease in the frequency of neural tube defects in pregnant women but also had the added advantage for the general public that there was a highly significant fall in the risk for stroke (2).
More than 30 countries around the world now follow the same procedure and practice mandatory folic acid fortification of staple foods. As yet, Europe has not followed with a mandatory fortification procedure, but here too, fortification is an option. If fortification is done through staple foods (e.g., flour and salt), broad sections of the population can be reached if they take advantage of voluntary fortification and give preference to fortified products.”
Bonn, April 2010