Should you take folic acid? Too much may cause cancer; additional research suggested

Folic acid is one of those great public health success stories. In the decade following fortification of cereal grains and other foods, the rate of certain birth defects dropped dramatically.

As studies started showing that folic acid also could help prevent cancers, it started to seem like a wonder vitamin.

Folic acid's heyday may be over. New studies suggest that getting too much folic acid might fuel certain cancers in some people.

And with the vitamin showing up in ready-to-eat cereals, bread, snack bars and multivitamins, some experts fear it's easy to exceed the recommended daily intake of 400 micrograms. There is an urgent need, some say, to figure out how much folic acid is enough but not too much for different segments of the population.

"Too little folic acid we know is not good, and too much folic acid is probably not good," says Connie Motter, a genetic counselor at Akron Children's Hospital in Ohio and co-chair of the National Council on Folic Acid, a coalition of advocacy groups. "The answer is not going to be easy."

Folic acid is the synthetic version of folate, vitamin B9, which is found naturally in such foods as leafy greens, orange juice and legumes. It helps the body make and maintain new cells. The United States began requiring fortification of flour and several other cereal grains in 1998, after studies linked folic acid deficiency with spina bifida and anencephaly, two potentially devastating birth defects. Since then, the rate of both defects has declined by 20 percent to 50 percent.

No one disputes that women should have adequate amounts of folic acid in their bodies at conception. The first few weeks of pregnancy are especially critical. And because more than half of pregnancies are unplanned, doctors recommend that all women of childbearing age take a daily supplement of up to 800 micrograms.

Getting enough folate also may protect against anemia, premature birth and congenital heart defects, and keeps hair, skin and nails healthy.

But scientists also know that excess folic acid can cover up a shortage of the vitamin B12, a common condition in older people that can cause dementia if unaddressed.

Then there's cancer. The vitamin can help prevent development of certain cancers, particularly in the colon, where cells replicate especially fast. Studies show that people who get plenty of folic acid reduce their risk of developing colorectal cancer and precancerous polyps by 40 percent to 60 percent.