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High dose folic acid (0.8 mg/d) + vitamin B 12 may increase cancer and cancer deaths

Henry I. Bussey, Pharm.D., FCCP, FAHA
March, 2010

ClotCare previously reviewed data that found no benefit of using folic acid supplementation to reduce homocysteinemia levels - - but whether such therapy might have a harmful effect was not addressed. In a recent issue of JAMA, investigators report a substantial increase in both the incidence of cancer and cancer-related mortality in those patients who received high dose (0.8 mg) folic acid plus B12 supplementation (

Specifically, the investigators evaluated the combined data from two randomized Norwegian studies. A total of 6,837 patients were followed for a median of 39 months in the studies and an additional 38 months of post-study observation. The studies included 4 arms:

  1. folic acid 0.8 mg/d + B12 0.4 mg/d + B6 40 mg/d
  2. folic acid 0.8 mg/d + B12 0.4 mg/d
  3. B6 40 mg/d
  4. placebo

There were just over 1,700 patients in each of the 4 treatment arms.

The incidence of cancer was 10% (341 cases) in those who received folic acid + B12 vs. 8.4% (288 cases) in those who did not receive folic acid + B12 [HR = 1.38, 95% CI = 1.07 - 1.79; p = 0.02]. Similarly, cancer death rates were increased with folic acid + B12 [4% (136 deaths) vs 2.9% (100 deaths); HR = 1.38, 95% CI = 1.07 - 1.79; p = 0.01]. Total mortality also was higher in the folic acid + B12 patients [16.1% (548 deaths) vs. 13.8% (473 deaths); HR = 1.18, 95% CI = 1.04 - 1.33; p = 0.01]. An increase in lung cancer was identified as the main difference. The accompanying editorial ( calculated that the impact of such folic acid + B12 supplementation would have the following impact on the population (expressed as events per 1000 individuals per year): 3.5 excess cases of cancer, 1 excess case of lung cancer, and 1.7 excess cancer deaths.2

For those of us in the U.S. where folic acid fortification of flour and grains has been mandated since 1998, this news of harmful effects of folic acid + B12 supplementation could be especially worrisome - especially since the two studies were performed in Norway where foods are not fortified with folic acid. However, according to the editorial mentioned above, supplementation of foods in the U.S. has increased the intake of folic acid by only about 100 mcg per day (compared to 800 mcg dose in the two studies). Also the editorialists refer to animal data that suggest that low doses of folic acid may actually have an anti-cancer effect while larger doses may promote malignant cell growth ( Lastly, the incidence of several cancers (including lung cancer) has declined since folic acid supplementation was mandated in the U.S.


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

  2. Drake BF and Colditz GA. Assessing cancer prevention studies - A matter of time. JAMA 2009; 302:2152-2153
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Friday, June 14, 2024