Folic acid doubts
Adding folic acid to flours, pastas and rice has reduced the rate of spina bifida and anencephaly in the U.S., sparing 1,000 babies each year from these devastating birth defects.
But a recent study suggests those health gains may have come at a cost: an extra 15,000 cases of colon cancer annually.
The report, from Tufts University, is the latest to raise a cautionary note about a public-health policy that has been largely viewed as a success.
“Have we done more harm than benefit?” said Dr. John Potter, a colon cancer expert at the Fred Hutchinson Cancer Center in Seattle, who was not connected to the latest research.
Writing last month in the journal Cancer Epidemiology Biomarkers and Prevention, scientists reported that colon cancer cases in the U.S. spiked after manufacturers began fortifying cereal grains with folic acid in the late 1990s. They saw a similar trend in Canada, which began fortification around the same time.
The pattern was surprising, researchers said, because colon cancer rates had been steadily dropping since the mid-1980s. Greater consumption of folic acid looked like the explanation.
Joel Mason, lead author and professor of nutrition science and policy at Tufts, said the report does not prove that extra dietary folic acid causes colon cancer but does suggest fortification may have unforeseen trade-offs.
Nutritionists have long known that younger women need 400 micrograms of folic acid daily to reduce their chances of giving birth to infants with neural tube defects, caused by the failure of the fetal spinal column to fully close.
Although rare, such defects are devastating. Spina bifida can cause paralysis, and infants with anencephaly -- in which much of the brain does not develop -- are stillborn or die soon after birth.
Since 1998, U.S. food manufacturers have been required to add 140 micrograms of folic acid to each 100 grams of cereal grains that are labeled “enriched.” Breads, cereals and other grain-based foods shipped across state lines are all fortified with folic acid, a B vitamin naturally found in green leafy vegetables, fruits, dried beans and nuts.
In only a few years, the rate of neural tube defects in the U.S. fell, from 10.6 per 10,000 births in 1996, before fortification, to 7.6 per 10,000 births in 2000.
Canada also saw a sharp decline -- to 8.6 per 10,000 births in 2002 from 15.8 per 10,000 births in 1993, according to a report published last month.
Those results deepened the desires of some scientists and health advocates for even greater improvements. The nonprofit March of Dimes, which has long endorsed increased fortification, is preparing a petition asking the Food and Drug Administration to further boost folic acid levels in cereal grains. Acting medical director Dr. Michael Katz, who called the colon cancer studies unconvincing, said the nonprofit would request at least a doubling of current levels.
The March of Dimes said government surveys show that many women ages 18 to 45 do not receive adequate amounts of folic acid in their diets. In fact, the majority of those women consume about 130 micrograms of folic acid daily, well below the recommended dose, according to R.J. Berry, an epidemiologist at the national Centers for Disease Control and Prevention.
But some researchers have cautioned against increased fortification because of possible downsides. Folic acid can mask symptoms of vitamin B-12 deficiency, common in the elderly. Unaddressed, a B-12 lack can lead to neurological problems.
Some researchers now caution against adding more folic acid to the diet until the possible cancer link is better understood.
“This is not the right time to be moving ahead and increasing the level of folic acid in the food supply,” Mason said.
Dr. Arthur Schatzkin, chief of the nutritional epidemiology branch at the National Cancer Institute, said that although recent studies have raised red flags, the evidence favoring fortification is strong. Still, “when you focus on a magic bullet, sometimes you find collateral damage,” he said.
Not long ago, it was thought that almost everyone stood to benefit from taking large amounts of folic acid, which had been linked to a decreased, not increased, risk of colon cancer.
That belief was challenged in June when researchers reported in the Journal of the American Medical Assn. that large daily doses of folic acid did not reduce development of precancerous growths called adenomas. The 1,000-patient study of people with a history of adenomas also found folic acid seemed to increase their colon cancer risk.
Mason said the study and his own research suggest the biology of folic acid is complex and related in part to the amount of the vitamin consumed and the age of the person taking it.
Folic acid has a critical role in cell replication, he said, and can protect against copying errors that can turn normal cells cancerous. But excess amounts of the vitamin seem to speed replication of precancerous cells, he said, potentially helping them turn cancerous.
The risk of colon cancer increases with age. One-third to one-half of adults older than 50 have precancerous cells in their intestines, he said, so too much folic acid could put them at even greater risk.
About 130,000 Americans are diagnosed with colon cancer each year, and 56,000 of them die from it.
Still, Mason and others said it was premature to stop folic acid fortification altogether. “Can we make a case that more people are at risk of developing colon cancer than are at risk of developing neural tube defects? We really don’t have the answers,” Potter said.
People older than 50 and others at risk for colon cancer can protect themselves via regular screenings for precancerous polyps, which sharply reduce the chances of developing the disease, he said.
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