How Much Folic Acid is Safe?
New Research Suggests That Too Much Folate Can Be Dangerous
Oct 18, 2009
Folic acid - vitamin B9 - has been a great public health success story. Since 1998, when the US began requiring fortification of cereal grains and other foods with folate, the rate of certain birth defects, most notably spina bifida and anencephaly, has dropped dramatically. And as studies beginning in the 1980s started showing that folic acid could also help prevent some cancers, some wondered if it could be a kind of miracle vitamin.
New research, however, has revealed that folate's potential may not be as enormous as once thought. Rather than preventing cancer, it seems that too much folic acid could increase the risk of certain cancers. The question is -how much folate is too much?
Many Packaged Foods are Fortified With Folic Acid
Required fortification of processed foods, along with increased public awareness of folic acid's benefits, could be a dangerous equation, some experts now say. The recommended daily intake of folic acid - 400 micrograms - may be far exceeded by people who eat fortified products along with multivitamins containing folate. What's needed now, these experts say, is a clear determination about how much folate should be consumed by people in different categories. For example, it is well accepted that pregnant women can benefit from extra folate, which stimulates healthy cell growth. For others, however, such as those at risk for certain kinds of cancers, the same amount of folate currently prescribed to pregnant women may be too much.
Who is at Risk?
When it comes to cancer, the effects of folate are somewhat mystifying. For example, studies have shown that people who get plenty of folic acid reduce their risk of developing colorectal cancer and precancerous polyps by 40% to 60%. The problem is that folic acid doesn't just help healthy cells grow. It also helps cancerous cells grow. Animal studies have shown that once cells become malignant, folic acid may make things worse.
The findings of a 2007 study indicate that rates of colorectal cancer went up in North America around the same time that fortification began. While researchers acknowledge this could be a coindicence, it appears that the rates of such cancers also increased in Chile after folate supplementation began there in 2000. The study estimates that excess folic acid consumption may cause an extra 15,000 cases of colorectal cancer each year in the U.S. and Canada. By comparison, fortification with the vitamin prevents an estimated 2,000 to 3,000 brain and spinal cord defects in both countries.
Folic acid's effects have also been tested in clinical trials. The largest such study involved approximately 1,000 people who had had precancerous polyps removed from their colons. Half of the patients were given a daily supplement of one milligram of folic acid (2.5 times the recommended intake of 400 micrograms), while the others took a placebo.
When surveyed several years later, people in the folic acid group were found to be more than twice as likely to have three or more polyps in their colons. Male participants in the study who had taken folic acid supplements were nearly three times as likely to develop prostate cancer up to a decade later. (Journal of the American Medical Association - March, 2007).
As early as the 1940s, folic acid supplements were found to speed the progress of leukemia in children who were given the vitamin in the hope that it might help. Such studies helped lead to a class of antifolate drugs that are among today's most common cancer treatments.
While the current research does not suggest people should stop taking folic acid supplements altogether, the information learned will inevitably lead to clearer recommendations for people in high risk groups.
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