Folate is a B vitamin that helps cells grow and divide. Folic acid is the form of folate that’s added to foods and supplements.
Women need the vitamin early in their pregnancy—often before they know that they’re pregnant— to reduce the risk of spina bifida and other neural tube defects. (The incidence of spina bifida has dropped by 31 percent since 1998, when the Food and Drug Administration started requiring companies to add folic acid to most breads, pasta, rice, cereals, and other grains.)
So, women who could become pregnant should get 400 micrograms of folic acid daily and a multivitamin is a convenient and inexpensive way to ensure that.
For other individuals, some researchers worry that too much folic acid from a combination of supplements, grains, and fortified breakfast cereals may harm those who unknowingly harbor pre-cancerous or cancerous cells in their body.
“If you’ve done studies in cells and in animals, as I have, you know that consuming too much folic acid can enhance the development of cancer,” says Joel Mason, director of the Vitamins and Carcinogenesis Laboratory at the Human Nutrition Research Center on Aging at Tufts University.
“If you think about the role folate plays in the cell, helping to synthesize new cells, this makes eminent sense.”
But a meta-analysis published in 2013 eased some of the fear. In 13 randomized controlled trials that included 50,000 people, those who took an average of 2,000 micrograms of folic acid every day for five years had no higher risk of any kind of cancer than those who got a placebo. Most multivitamins have only one-fifth that much (400 mcg).
Mason is still uneasy. “It typically takes eight to 12 years for a tiny precancerous bump in your colon to fully evolve into a true cancer,” he says. “So it’s possible that the trials weren’t long enough to see the effects of folic acid on cancer risk.”
Still, “the good news is that if folic acid does increase the risk of cancer, you’d have to take a fair bit for that to happen,” notes Mason. “It’s probably safe to take the folic acid in a single multivitamin each day.”
The Institute of Medicine says that 1,000 micrograms of folic acid a day is the highest safe level adults can consume, because more than that can cover up a vitamin B-12 deficiency.
Americans get an average of about 270 mcg a day of folic acid from fortified grains (bread, pasta, rice, etc.) and breakfast cereals. But that average includes people who eat a cereal like Kellogg’s Raisin Bran, which has 100 mcg of folic acid (the label says “25% DV”) in every cup and those who eat All-Bran, which has 400 mcg (“100% DV” on the label) in every half cup.
“If you took a multivitamin in the morning, a B complex in the afternoon, and ate cereals and energy bars fortified with folic acid, you could exceed 1,000 micrograms of folic acid a day,” says Mason. “That could mask a B-12 deficiency and possibly increase cancer risk.”
Source: Lancet 381: 1029, 2013.