Folic acid, B12 and cancer

November 19, 2009 7:56:35 AM PST
Folic acid is an important and valuable vitamin in our diet, and a critical one for pregnant women to help prevent birth defects. But a new study from Norway is raising questions about high doses and a link to cancer. It's a study where the results are not what the scientists expected. So when that happens, they always need to take a closer look.

But we need to be careful about two points: folic acid is important in the right doses, particularly for pregnant women, and taking high doses to any supplement could be problematic. The study certainly raises that question.

In the study, published in the Journal of the American Medical Association, folic acid at twice the rate than is recommended in this country was given to heart patients in Norway. So was vitamin B12, which was given at 20 times the rate recommended in the U.S.

Patients took them for 3 1/2 years.

Three years after that, two studies revealed the following findings. Cancer developed in 10 percent of the patients who took the supplements, compared to 8.4 percent of those who did not take any supplements.

That's an increase of 21 percent.

Elise Zied is with the American Dietetic Association.

"These were amounts of folate and B12 that were much higher than people normally consume," she said. "It's not a big increase in cancer incidence, but what's interesting is that most of the cancer occurred in people who smoke or previously smoked."

But was it only the high doses that increased the cancer risk?

Smokers and former smokers made up 90 percent of the people who developed lung cancer, which made up one third of the cancers found.

In this country, folic acid is added to our cereals and grains, and it has been proven to reduce birth defects. It is also found in leafy green vegetables and beans. But for people who require supplements, staying within the limits of recommendation is important.

An editorial in the journal says it make take decades before we fully understand exactly how folic acid affects health. One expert theorizes folic acid may be helpful at one point, such as in pregnant woman, but not at another, such as a smoker.

What is already known is that high doses of supplements can be dangerous.

"You always have to ask, what do we know about the benefits and what do we know about the risks," Dr. Richard Bessler said. "And this is a potential risk."