It is one of the best things a pregnant woman can do to protect her unborn baby from birth defects. But a new U.K. study is raising concerns about a potential cancer risk associated with taking folic acid (search).

The preliminary findings suggest that taking very large doses of folic acid during pregnancy may slightly increase a woman’s risk of dying from breast cancer (search) decades later. But a nutrition researcher interviewed by WebMD called the findings a “statistical fluke,” adding that other studies have shown folic acid supplementation to protect against breast cancer, as well as colorectal cancer and heart disease.

“This (study) is not even a molehill compared to the mountain of evidence that we have showing folic acid supplementation to be beneficial,” says Emory University research professor Godfrey P. Oakley, MD.

Women Took Huge Doses

The study included some 3,000 women who had taken part in a trial of folic acid supplementation during pregnancy in the 1960s. At the time, the women took either 0.2 or 5 mg of folic acid a day or a placebo throughout their pregnancies.

These days, it is generally recommended that pregnant women or women who might become pregnant take 400 micrograms of the vitamin daily. The women in the 1960s trial taking the largest dose of folic acid took more than 10 times that amount.

Researcher Marion Hall, MD, of Scotland’s University of Aberdeen, tells WebMD the initial purpose of the study was to see if folic acid supplementation helped protect the women against death from heart disease years later.

A review of medical records in 2002 revealed that 210 of the women had died since participating in the trial almost four decades earlier. Forty of the deaths were related to heart disease, 112 women died of cancer, and 31 of those deaths were from breast cancer.

The death rate among women taking folic acid was slightly higher than that among women who did not take the vitamin, but no difference was seen in the incidence of cardiovascular deaths.

The risk of death from breast cancer in women taking the largest dose of the vitamin was twice that of the women taking a placebo in the study. But the researchers warn that the overall number of deaths was too small to prove an association. Their findings are published in the Dec. 11 issue of the British Medical Journal.

“This was an unexpected but also a very preliminary finding, and further research will be required to ascertain whether this is a true finding,” Hall says. “Nobody needs to stop taking folic acid based on this study. But I think policy makers here would be well advised to take this information into account in their decision making.”

The Fortification Debate

The “decision making” Hall is referring to is the debate in the U.K. over whether to add folic acid to the food supply, as has been done in the U.S. and many other industrialized countries.

Folic acid was added to breads, cereals, flours, and other grain products in the U.S. in 1986. Since that time, neural tube-related birth defects, such as spina bifida, have declined by 26 percent, according to the CDC.

Government research also suggests that fortification is responsible for preventing as many as 31,000 deaths from stroke each year. High levels of a substance called homocysteine in the blood increase the risk of stroke, and folic acid helps bring that level down.

“It is a real tragedy — a huge public policy failure — that fortification has not happened in [the U.K.], and the danger is that this study will influence that debate,” Oakley says.

In an editorial accompanying the study, Oakley wrote that mandatory fortification “should be immediately implemented for the known benefits of preventing birth defects and anemia.”

Though she acknowledges that fortification may benefit the public as a whole, Hall says the unanswered questions about the potential long-term risks of folic acid supplementation need to be explored.

“I think policy should be made on the basis of all the information that is available, and that would include this study,” she says.

By Salynn Boyles, reviewed by Michael W. Smith, MD

SOURCES: Charles et al., British Medical Journal, Dec. 11, 2004; vol 329: pp. 1375-1376. Marion H. Hill, professor emeritus, University of Aberdeen, Scotland. Godfrey P. Oakley, MD, research professor, department of epidemiology, Rollins School of Public Health, Emory University, Atlanta.