Folic Acid, B12 May Increase Cancer Risk
Study Shows Slight Increase in Cancer Risk From Large Doses of Supplements
WebMD News Archive
Nov. 17, 2009 -- There is new evidence that folic acid, taken in large
doses, may promote some cancers.
Heart patients in Norway who took folic acid and vitamin B12 supplements
were found to have a slightly increased risk for cancer and death from all
causes, compared to heart patients who did not take the supplements in a study
published in TheJournal of the American Medical Association.
Unlike the U.S., Norway does not fortify flour and grain food products with
folic acid, which is the synthetic form of the B vitamin folate.
Because of this, Norwegians tend to have much lower blood folate levels than
Americans, making the population a good one for studying the impact of folic
acid supplementation on cancer risk, study researcher Marta Ebbing, MD, of
Norway's Haukeland University Hospital tells WebMD.
Folic Acid, B12, and Lung Cancer
Ebbing and colleagues analyzed data from two studies that included almost
7,000 heart patients treated with B vitamin supplements or placebo for an
average of three and one-half years between 1998 and 2005.
The original intent of the studies was to determine if taking vitamin B
supplements improved cardiovascular outcomes, which it didn't do.
During treatment, blood folate levels among patients who took 0.8 milligrams
a day of folic acid plus 0.4 milligrams a day of vitamin B12 increased more
The patients were followed for an average of three years after
supplementation ended, during which time 341 patients who took folic acid and
B12 (10%) and 288 patients who did not (8.4%) were diagnosed with cancer.
Folic acid and B12 supplementation was associated with a 21% increased risk
for cancer, a 38% increased risk for dying from the disease, and an 18%
increase in deaths from all causes.
This finding was mainly driven by an increase in lung cancer incidence among
the folic acid and B12-treated patients.
Seventy-five (32%) of the 236 cancer-related deaths among the study
participants were due to lung cancer, and the cancer incidence among the study
group was 25% higher than in the population of Norway as a whole.
Roughly 70% of all the patients in the study were either current or former
smokers, including more than 90% of those who developed lung cancer.