Reports have been surfacing that extra supplementation with folic acid may be related to certain cancers. You may have read recent headlines about the newest study out of Norway that showed an increased risk of cancer in people who took high doses of folic acid.

Doesn't Folic Acid Prevent Cancer? There is strong evidence that getting enough folic acid can help lower your chances of getting certain cancers. Folic acid plays a role in the growth and repair of cells. Some studies show that folic acid blocks cancer in its early stages. The evidence for prevention is strongest for colorectal cancer. But getting too much folic acid could have the opposite effect by causing cancer cells to grow more easily. The key seems to be getting the right amount of folic acid - not too little and not too much.

How Strong is the Evidence?  These most recent studies showed a small increased risk of cancer. In the group that researchers supplemented with folic acid, 10.0% died of cancer while 8.4% of the people in the group that did not get folic acid died of cancer. In the second study, the difference was 4.0% cancer deaths in the folic acid group compared to 2.9% in the group that did not get folic acid. So you see, the increased risk of cancer with folic acid supplements was really small.

How Much Folic Acid is too Much? In these studies, the group that was getting folic acid got 800 micrograms a day. You need 400 micrograms folic acid a day. Most multivitamin pills have 400 micrograms. That's the same as "100% of the Daily Value".  

The problem is that many foods have folic acid added to them. All grains in the United States must have 25 micrograms of folic acid added per serving. That is not enough to be a problem. However, some cereals add a lot more than 25 micrograms. Some cereals have 400 micrograms of folic acid in one serving. That's the same amount that it is your multivitamin tablet! That could bump your intake up to 800 micrograms or more a day.

What Should You Do? Don't panic. Here is my advice for getting enough folic acid to prevent cancer but not enough to increase your risk of cancer!

If you take a multivitamin:

    • Make sure it has no more than 400 micrograms (100% of the Daily value) of folic acid.
    • Avoid cereals with 100% of the daily value for folic acid
    • Don't take an extra folic acid supplement unless your doctor recommended it.

 Remember, getting the right amount of folic acid may be important for cancer prevention, lowering the risk of neural tube defects in a developing fetus, and good health in general. Too much folic acid may be related to a slightly increased risk of cancer.

Beth Kitchin MS RD
Assistant Professor
UAB Department of Nutrition Sciences

Ebbing M, Bonaa KH, Nygard O, et al. Cancer incidence and mortality after treatment with folic acid and vitamin B12. JAMA. 2009;302(19):2119-2126.