Folic acid fortification: reduces birth defects, but may cause extra cancers

Nutritional and vitamin supplements are again in the news. Folate (also known as folic acid), long considered to be essentially beneficial, now has been shown to have some potential downsides. The article below, excerpted from Harvard Women's Health Watch, discusses both the incredibly important benefits of this vitamin, and also some risks.

Personally, I had been taking supplemental folic acid, upon the suggestion of my internist. However, when the link between these supplements and polyps and colon cancer were disclosed, I stopped taking the supplement. I also paid greater attention to how much folic acid I was getting through fortified foods.

Deciding what medications, vitamins, and supplements to take is always a tough decision. Consulting with your doctor about taking or not taking folic acid is the best advice. Here's the article from Harvard Women's Health Watch:  

Folic acid is a synthetic form of folate, a B vitamin found naturally in various fruits, vegetables, and legumes. We need folate to produce and maintain new cells (in particular, red blood cells) and to keep nerve cells functioning properly. It also helps prevent DNA changes that may lead to cancer.

There's abundant evidence that women who take folic acid supplements during the very early stages of pregnancy can prevent neural tube defects such as spina bifida in their babies. That explains the drive for folic acid fortification of grain and cereal products, which became mandatory in the United States and Canada in 1998. But there's also evidence that the added folic acid is contributing to colorectal cancers.

Effects of folic acid fortification

In countries that require folic acid fortification, including the United States and Canada, the rate of neural tube defects has fallen by 25% to 50%. However, about the time that fortification was mandated, there was also an uptick in colorectal cancer.

Researchers at Tufts University, working with large population-based cancer registries, studied trends in colorectal cancer from 1986 to 2002 in the United States and Canada. The results, published in the July 2007 issue of Cancer Epidemiology Biomarkers and Prevention, showed a 15-year decline that was suddenly reversed in the early fortification years, when average blood levels of folate doubled. As a result, an extra four to six cases of colorectal cancer per 100,000 people per year — a total of 16,500 extra cases — were estimated to have occurred.

Although the chronological link between increased colorectal cancer cases and higher blood levels of folate isn't proof of cause and effect, the Tufts researchers think there are biological reasons why extra folic acid may be to blame. There's compelling evidence that high dietary intake of folate may protect healthy cells against colorectal and other cancers. But there's equally strong laboratory and clinical evidence that — under certain circumstances — folic acid can stimulate the growth of cancer cells.

This may also help explain the disappointing results of the Aspirin/Folate Polyp Prevention Study, published in the June 6, 2007, Journal of the American Medical Association. That trial took place between 1994 and 2004 and involved 1,021 men and women who had all had procedures to remove adenomatous polyps (the kind most likely to turn into cancer). To find out if folic acid would prevent more polyps from developing, researchers assigned subjects to receive either 1,000 mcg of folic acid per day or a placebo.

Colonoscopies performed after three years and again three to five years later found little difference in the incidence of adenomas. But at the second follow-up, the subjects taking folic acid had nearly double the rate of advanced adenomas and were more than twice as likely to have three or more precancerous polyps. This study doesn't tell us whether folic acid supplements prevent or promote the development of polyps in the first place. But it raises concerns about the effects of excessive folic acid from both supplements and fortification, especially on people ages 50 and over, who are more likely to already have polyps.

The bottom line

Unless you're pregnant or lactating or have a recognized folate deficiency, the recommended daily intake of folic acid is 400 mcg per day — the amount found in a typical multivitamin. According to Dr. Walter Willett, Chairman of the Department of Nutrition at the Harvard School of Public Health, "the added folic acid from food fortification is on average 100 to 200 mcg per day, but this varies widely, depending on food choice." The tolerable upper intake level (UL) — the maximum safe amount — of folic acid from fortified foods and supplements is 1,000 mcg per day. With all the fortified foods on the market, you may exceed that limit, especially if you're already taking a daily multivitamin containing 400 mcg of folic acid. So it's a good idea to check the nutrition labels of cereal and grain products to find out how much you're getting from fortified foods.

There's no known health risk from foods naturally high in folate, nor is there a UL for naturally occurring folate in foods, so try to get as much of your daily requirement from a healthy diet that includes fruits, vegetables, and legumes, which also have many other important nutrients. If you need more, take a multivitamin.

Marc Garnick, M.D., is an internationally renowned expert in medical oncology and urologic cancer, with a special emphasis on prostate cancer. He is a Clinical Professor of Medicine at Harvard Medical School and maintains an active oncology practice at Beth Israel Deaconess Medical Center. Dr. Garnick serves as Editor in Chief of Perspectives on Prostate Diseases, a quarterly report from Harvard Health Publications.

Vitamins and Minerals
Vitamins and Minerals: What you need to know is a special health report from Harvard Medical School that provides the latest information on vitamins and minerals so that you can make healthy choices about what foods to eat and what supplements to take. Because nutritional science continues to evolve, this report also contains tips on how to judge new studies on vitamin benefits and put the findings in context.

Are you Living With Cancer? Connect with others with similar health concerns and issues. Click hereto join the group.