Is there such a thing as too much folic acid?

Some scientists suggest that folic acid -- known for preventing birth defects -- may come with a downside.

By Catherine Price
January 29, 2008 11:53PM (UTC)
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There were certain things I thought were supposed to be unquestionably good for you. Like, for example, eating vegetables. Or drinking enough water. Or taking folic acid.

In fact, just this month, the American Journal of Obstetrics and Gynecology published a study suggesting a link between folic acid and the prevention of preeclampsia, a leading cause of maternal and infant illness and death. But despite its well-documented effects on preventing birth defects like spina bifida, folic acid may soon come under fire for a possible side effect: accelerating the development of precancerous growths, especially in the colon, into cancer. (Some researchers also think folic acid may be linked to higher rates of prostate cancer and impaired mental functioning in the elderly.)


The Baltimore Sun has a report on what some researchers think may be the downsides of folic acid -- which are probably worth investigating, since in the United States, flour, bread and pasta (and many breakfast cereals) are fortified with it. Joel Mason, director of the Vitamins and Carcinogenesis Laboratory at the U.S. Department of Agriculture's Human Nutrition Research Center at Tufts University (whew) is quoted as saying, "There's an increasing level of concern that [folic acid fortification] might be harming some segments of the population." It's because of such concerns that the United Kingdom has "put a hold on its efforts to require folic acid fortification," reports the Sun. (In the United States, on the other hand, lobbying efforts are under way to increase the amount of folic acid in fortified foods -- partly because other researchers believe that folic acid may help prevent some cancers, strokes and cardiovascular disease.)

While it seems a bit questionable to me to link an overall increase in colorectal cancer with a nationwide fortification program (after all, there could be plenty of other variables at work), there are some concrete reasons to think that folic acid help cancerous cells reproduce. As the article explains, "In normal tissue, [folic acid] helps cells to divide and grow and proliferate. In cells where cancer is just beginning, folic acid is believed to have the same effect -- causing fast-growing cancer cells to reproduce even more rapidly." This effect was documented in the 1940s, when leukemia patients who were given high doses of folic acid showed accelerated cancer growth.

Are the potential risks of folic acid great enough to outweigh the proven benefits? Should we stop fortification? Most doctors seem to think not -- partly because the folic acid in fortified flour and pasta makes up only a small amount of most people's intake of folic acid. Also, just as it takes time to prove a benefit, it takes time to measure the potential consequences -- and for the moment, there are more known benefits to folic acid than there are risks. Walter Willet, chairman of the department of nutrition at the Harvard School of Public Health, gets the article's closing quote: "Given the overall picture, if there is any negative impact, it is counterbalanced by other positive trends," he says. "I think we've done something that overall is beneficial, and we won't know the full balance of benefits, or possible adverse effects, for many years. But overall, the picture looks good."


(If you want to get folic acid from foods other than fortified grains, it exists naturally in broccoli, oranges, peas, asparagus, bananas and many nuts.)

Catherine Price

Catherine Price is an award-winning journalist and author of Vitamania: How Vitamins Revolutionized the Way We Think About Food. Her written and multimedia work has appeared in publications including The Best American Science Writing, The New York Times, Popular Science, O: The Oprah Magazine, the Los Angeles Times, The San Francisco Chronicle, The Washington Post Magazine, Salon, Slate, Men’s Journal, Mother Jones, PARADE, Health Magazine, and Outside. Price lives in Philadelphia.

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