A Closer Look at B-Vitamins and Cancer Risk
A study published in the Journal of the American Medical Association (JAMA) reports that high intakes of folic acid and vitamin B12 may increase the risk of cancer, deaths from cancer, and mortality from all causes in people with ischemic heart disease, in which reduced blood supply to the heart causes chest pain and difficulty exercising. The study’s surprising results have spurred a flurry of concern from some and backlash from others, as we try to gain a better understanding of the real risks of supplementing with or fortifying foods with these essential vitamins.
What did they find?
Combining the results of two previous studies of more than 6,800 Norwegians with ischemic heart disease, researchers aimed to determine whether supplementing with folic acid, vitamin B12, and vitamin B6 affects cancer risk. Since Norway does not fortify foods with folic acid, this seemed an ideal population in which to study the effects of supplementation.
The study found that after 39 months of treatment, people who took 800 mcg of folic acid plus 400 mcg of vitamin B12 each day were significantly more likely to be diagnosed with cancer, die from cancer, and die from any cause, compared with people who did not supplement with the vitamins. Vitamin B6 was not associated with increased cancer risk.
Lung cancer accounted for most of the increased risk, causing the researchers to conclude that taking folic acid and vitamin B12 increases the risk of lung cancer. However, 94% of the people who were diagnosed with lung cancer during the study were either current or former smokers, making smoking an equally suspect (and well-established) culprit. The findings raise the possibility that there is a toxic interaction between cigarette smoke and folic acid or vitamin B12. Such an interaction has previously been demonstrated with beta-carotene and smoking. In lieu of additional research, one cannot necessarily generalize the findings from the new study to nonsmokers.
Folic acid: friend or foe?
Folic acid is a key player in cell development; low folic acid status in pregnant women is associated with neural tube defects (like spina bifida) in their infants, and animal studies suggest that folic acid deficiency could lead to the development of cancer. Too much folic acid might have an opposite effect, though, actually speeding the growth of cancerous cells.
During the 1990s, many countries began fortifying foods with folic acid, a nutrient that is lost in the process of refining grains. (The other obvious solution would be to encourage people to opt for more whole grains and forego processed foods altogether, but that’s another story.) Since fortification began in the US, the incidence of neural tube defects has dropped substantially, and one analysis showed that colon cancer and overall mortality have both decreased significantly, a finding that stands in contrast to those of the new study.
Food for thought before you ditch folic acid
If folic acid increases lung cancer risk, one would expect the incidence of lung cancer to have increased in parallel with folic acid fortification, but in fact this isn’t what we’ve seen. Lung cancer rates have been steadily declining over the past two decades. According to an editorial in JAMA regarding the new study, “these national incidence rates do not support a substantial, population-wide adverse effect of the magnitude suggested by (the authors).”
Another concern about the validity of the new study’s results is whether the duration of the study was long enough to draw meaningful conclusions about cancer risk. After all, the development of cancer is dependent on many factors, and it takes a long time—often several decades—to develop. So, while cancer risk did appear to increase in the group who received folic acid, it is almost impossible to attribute that risk solely to folic acid intake.
Because the study’s participants already had heart disease, the results cannot be generalized to a healthy population. Further, the original studies were designed to assess the effect of B-vitamin supplementation on future heart disease risk—not on cancer risk. Studies that attempt to ask new questions by re-analyzing old data have a relatively high potential for error.
The Council for Responsible Nutrition pointed out in a response to the new study that while “it is puzzling why patients who were given high doses of folic acid were more likely to develop lung cancer…these results are inconsistent with the larger body of data,” and that “this effect has not been observed previously.” The authors of the JAMA editorial concluded that “the findings do not nullify the potential long-term benefits that folic acid fortification may have on population health.”
What we do know
- More studies specifically designed to assess cancer risk in relation to folic acid intake are needed.
- For now, it seems reasonable and safe to take folic acid at lower doses (less than 800 mcg per day) and to eat folic acid-fortified foods.
- Leading a healthy lifestyle can help prevent the majority of cancers: don’t smoke, get regular exercise, maintain a healthy weight, and eat a balanced diet including plenty of fresh brightly colored fruits and vegetables.
November 25, 2009
Kimberly Beauchamp, ND, earned her bachelor’s degree from the University of Rhode Island and her Doctorate of Naturopathic Medicine from Bastyr University in Kenmore, WA. She cofounded South County Naturopaths in Wakefield, RI, and now sees patients in East Greenwich and Wakefield. Inspired by her passion for healthful eating and her own young daughters, Dr. Beauchamp is currently writing a book about optimizing children’s health through better nutrition.
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