Chances are, you started your day with a generous helping of folic acid. For more than a decade, the government has required enriched grains -- most notably white flour and white rice--to be fortified with folic acid, the synthetic form of the B vitamin folate.

Many food manufacturers take it further, giving breakfast cereals, nutrition bars, and beverages a folic acid boost too. The extra nutrient isn't meant for you, though -- it's added to protect fetuses from developing rare but tragic birth defects.

The fortification effort appears successful: Since 1998, the number of these birth defects dropped by about 19%. But for women past the years of having children, as well as for men of any age, unnatural dosages of this nutrient don't seem to be helpful--and may even be harmful. Indeed, many scientists have grown increasingly concerned about mounting research -- including a study published last winter in the Journal of the American Medical Association -- suggesting that all the extra folic acid might increase your odds of developing cancer.

"The more we learn about folic acid, the more it's clear that giving it to everyone has very real risks," says folic acid researcher David Smith, PhD, a professor of pharmacology at the University of Oxford in England.

If there's a nutrient it's easy to overdose on, it's folic acid. The vitamin is all around us, slipped into the cereal we eat for breakfast, the bread we eat for lunch, the energy bars we snack on, and the supplements that over one-third of us take regularly. Women are supposed to get 400 mcg a day, the amount that protects fetuses. Some cereals, though, contain more or have a serving size that makes it easy to pour a double dose. Add to that a vitamin washed down with your vitamin-fortified drink, and you may get a megadose before walking out the door.

The risk experts worry about most: colon cancer. Last year, health officials in Chile reported that hospitalization rates for colon cancer among men and women age 45 and older more than doubled in their country since fortification was introduced in 2000. In 2007, Joel Mason, MD, director of the Vitamins and Carcinogenesis Laboratory at the Tufts University School of Medicine, described a study of the United States and Canada suggesting that rates of colon cancer rose--following years of steady decline--in the late 1990s (around the time our food was being fortified). Better screening or an aging population could not explain the difference, which amounts to an additional 15,000 cases of cancer per year in the United States alone between 1996 and 2000, according to Mason's calculations. "It's a critical enough issue that it can't be ignored," he says.

Other research links high doses to lung and prostate cancers. In one study conducted in Norway, which doesn't fortify foods, supplementation with 800 mcg of folic acid (plus B12 and B6) daily for more than 3 years raised the risk of developing lung cancer by 21%. Another, in which men took either folic acid or a placebo, showed those consuming 1,000 mcg of folic acid daily had more than twice the risk of prostate cancer. And a new worry recently came to light when scientists discovered the liver has limited ability to metabolize folic acid into folate--which means any excess continues circulating in the bloodstream. "Unlike folate, folic acid isn't found in nature, so we don't know the effect of the excess," says Smith.

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Internet site reference: http://www.prevention.com/health/nutrition/healthy-eating-tips/is-your-breakfast-giving-you-cancer/article/7518212f04527210VgnVCM10000030281eac____