Research being presented this weekend at a meeting of the American Association for Cancer Research is raising some disturbing questions about the safety of folic acid.
Folic acid is the synthetic version of folate, a B vitamin found in green leafy vegetables and whole grains. It plays a crucial role in cell development by facilitating the synthesis and repair of DNA.
Studies have shown that the nutrient helps to prevent birth defects when women get enough of the vitamin before becoming pregnant. But several recent studies have suggested it may raise the risk of some types of cancer in men, such as colorectal cancer and prostate cancer.
Now, new research suggests it may even be hazardous if taken during pregnancy.
Dr. Young-In Kim, an associate professor of Medicine and Nutritional Sciences at the University of Toronto, has completed a study that found that when folic acid is given to pregnant rats, it boosts the risk of breast cancer in their babies.
"There are studies indicating that these changes are permanent and can be inherited to the next generation. So were talking about future generations, many generations to come, may have permanent effects from maternal folic acid supplementation," Kim told 麻豆影视.
"It makes me worry about the long term consequences of too much folic acid," says Kim.
Another study presented at the meeting found that the supplement created changes to the offspring's DNA, including affecting a process called methylation, in which genes are either silenced or activated. The changes could raise the risk of cancer in the offspring later in life, says author Karen Sie, a research scientist at the University of Toronto.
A decade ago, Canada started adding folic acid to white flour. The goal was to ensure pregnant women got enough to prevent birth defects. But with many women also taking folic acid supplements, there are worries some may be getting too much.
Europe and the United Kingdom have postponed plans to fortify foods with folic acid until long term effects are better understood. And some, including Toronto-based dietician Rosie Schwartz, think it may be time to rethink folic acid fortification here in Canada.
"I think what we really need is for companies to stop adding folic acid to food without there being a consensus as to whether they should be doing it," she says.
Others, such as Dr. Gideon Koren, director of the Motherisk Program at the Hospital for Sick Children in Toronto, note that rates of birth defects such as spina bifida and cancers such as neuroblastoma have plummeted since folic acid supplementation was begun. He believes that the known benefits outweigh theoretical risks.
"I think it is very important to remember that the scares about cancer are mostly from animal studies and laboratory studies, not from human experience," he says. "We are still awaiting to see such human experience."
Much of the research that has linked folic acid with cancer has found that it affects pre-cancerous cells, cells that are growing abnormally and could become cancerous. Since pre-cancerous cells divide more rapidly than normal cells, "feeding" them folic acid seems to help the cells to synthesize DNA more rapidly and thus proliferate.
Kim believes that people who have had cancer or pre-cancerous cells, or people who have a high risk for cancer because of their family history should not be taking folic acid supplements.
He hopes that further research will help to uncover whether there is a level of folic acid that doesn't raise cancer risks.
"We need to find the right, safe dose range of folic acid supplementation during the pregnancy to reduce birth defects but minimize other health negative consequences," he says.
Health Canada recommends all women of childbearing age take 0.4 mg of folic acid a day, but says taking more than 1 mg a day of folic acid without the advice of a doctor is not recommended.
"We continue to encourage all women who could become pregnant to take a daily supplement," the agency says on its website. "We caution against taking more than one multivitamin tablet a day, as excess amounts of certain vitamins can be toxic."
Waht should not be avoided are leafy green vegetables and other foods containing folate, a vitamin that the body can't store and one that most of us don't get enough of. While studies have questioned the safety of too much folic acid, none have found hazards associated with folate.
Dr. Joel Mason, director of the Vitamin and Carcinogenesis Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston, says it is possible that folic acid has characteristics that are unique to itself -- and not to more natural forms of folate -- that are responsible for the cancer link.
"That is speculation," he told CTV.ca earlier this year. "Unfortunately, this is a field that no one yet really understands well and so we're kind of stumbling in the dark a bit."
With a report from CTV medical specialist Avis Favaro and producer Elizabeth St. Philip
