Since fortification was mandated, the average level of folate in the blood of Americans has risen and the average level of homocysteine has fallen. 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. 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
