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Dr. Young-In J. Kim, Gastroenterology and Hepatology at St. Michael's Hospital and also a professor at The University of Toronto, poses for a photo with Folic Acid at the hospital in Toronto, Ontario, Canada. Kim led a study that found the daughters of rats who took folic acid supplements before conception, during pregnancy and while breast-feeding have breast cancer rates twice as high as other rats. They also had more tumours and developed them at a faster rate. Kim also says there is more research that needs to be done to determine whether the findings also apply to humans. While there are similarities in breast cancer in rats and humans, there are differences in how rats and human metabolize folic acid.Deborah Baic/The Globe and Mail

A vitamin considered so beneficial that pregnant women are instructed to take it and many foods are laced with it, may be too much of a good thing: scientists have found folic acid at elevated levels can cause cancer in a rat's offspring.

"There's a concern," said Young-In Kim, staff gastroenterologist at St. Michael's Hospital in Toronto. "But we don't want to panic the general public about this."

Published in the February edition of the journal Cancer Research, the study found that rats given folic acid supplements before conception, during pregnancy and while breastfeeding, produced female offspring with breast cancer rates that were twice as high as the control group.

"We actually assumed that giving folic acid to moms will reduce the level of breast cancer in their offspring," said Dr. Kim, a University of Toronto medical professor. "To our surprise, a folic acid supplementation to mothers is the opposite of what we expected."

Indeed, the female rat offspring also had more tumours and faster-growing tumours, suggesting the folic acid supplement created a rat susceptible to cancer.

"That's what science is all about," said Dr. Kim. "You have unexpected findings."

Though it is a study of rats, not people, Dr. Kim said he is concerned enough to suggest women of childbearing age be careful not to ingest too high a level of the B vitamin.

Earlier research has shown that at modest levels, folic acid prevents birth defects and some cancers, such as neuroblastoma and pediatric leukemia in humans, in addition to colon cancer in rats. At higher levels, however, Dr. Kim's research found it can actually promote the growth of breast cancer in rats.

"Folic acid supplementation can do two things: It can protect against certain cancers, but it can promote other cancers," said Dr. Kim. "It has a dual effect, depending on when you take it."

The findings have broad implications not only for pregnant women but also to a general public that may be unwittingly overdosing on it through multivitamins, protein bars, vitamin drinks and breads, cereals and pastas. Even some cancer survivors are told to take folic acid, the synthetic form of folate, a B vitamin that occurs naturally in leafy greens, grains and other foods.

Dr. Kim's study adds to a growing body of evidence and feeds concerns that a large number of Canadians are being needlessly exposed to high levels of a vitamin that could have deleterious health effects. A Norwegian study published in the Journal of the American Medical Association two years ago found heart disease patients treated with folic acid and B12 were more likely to be diagnosed and die from cancer than patients who did not receive those vitamins as treatment.

How the superstar vitamin made its way into boxes of enriched pasta, bags of white flour and packages of cornmeal can be traced back to 1998 when the Canadian and U.S. governments required food producers to add it to those products. That was done to ensure that women of child-bearing age consumed enough of the vitamin to prevent neural-tube defects such as spina bifida in their offspring.

With half of pregnancies unplanned and defects occurring in the first trimester, folic acid fortification was a smashing success, dramatically reducing neural-tube defects. That's because women who didn't know they were pregnant were consuming adequate levels of a vitamin they didn't know they needed.

As for what Canadians should do, Dr. Kim said they should consume folic acid at the recommended dose: 400 micrograms a day from all sources, whether natural or a supplement, adding that "anything above that, I'd be quite concerned about."

Part of the problem, however, can be trying to reach that recommended number. Some prenatal vitamins, for example, contain one milligram of folic acid, which is 2½ times the recommended daily dose and the same amount used in the animal study.

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