In normal tissue, it 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.
Chemically, folic acid is the synthetic form of folate, a member of the vitamin B family. Green leafy vegetables, dried beans and nuts are among the foods naturally rich in folate. But before flour-based products were fortified, dietary supplements were among the only ways that women of child-bearing age could ensure an intake of 400 micrograms a day - the dosage believed to prevent birth defects.
Not enough women did it on their own, which is why the U.S. turned to fortification. Today, some breakfast cereals alone contain 400 micrograms of folic acid per serving. Even so, the March of Dimes, a national advocacy group devoted to reducing birth defects, is considering petitioning the Food and Drug Administration to increase the amount of folic acid required in fortified foods.
The concept of fortification isn't new. One of the earliest successful efforts was the addition of iodine to salt in 1924 to prevent goiter and other symptoms of severe iodine deficiency.
Vitamin D was first added to milk in the 1930s to prevent rickets. When folic acid in flour and bread became mandatory in 1998, those staples had long been fortified with thiamin, niacin and riboflavin.
Dr. Frank Witter, a professor of gynecology and obstetrics at Johns Hopkins, said fortification isn't enough by itself. Some women still don't get the necessary folic acid. But he would not advocate an increase in fortification levels.
"We have to strike a balance," he said. "Even water, there's a downside for too much and a downside for too little. The fortification is probably at an adequate level. [But] you can't really count on any fortification process to completely correct a problem."
A study published last summer by Tufts' Mason and his colleagues suggested a possible link between folic acid fortification and U.S. and Canadian colorectal cancer rates, which are no longer declining as quickly as they once were.
Since the introduction of mandatory folic acid fortification in those two countries, an expected drop in colon cancer rates has shown an uptick, translating to as many as 15,000 extra cases of colon cancer in the U.S. annually and 1,500 in Canada - cases that researchers say might not have occurred without folic acid.
