Jan 28 People taking high doses of the B vitamin
folic acid are not at an increased risk of cancer, according to
an international analysis - easing some concern about the
possible side effects of national programs aimed to raise intake
of the vitamin.
The United States and Canada have required flour to be
fortified with folic acid since 1998, after deficiencies of it
in pregnant women were tied to brain and spinal cord birth
defects in their babies.
But fortification isn't required in Western Europe, for
example, partly out of concern that the extra folic acid might
slightly increase people's risk of cancer due to its role in
cell growth. Cells, including cancer cells, need folate - the
natural form of folic acid - to grow and divide.
"Folic acid supplementation does not substantially increase
or decrease incident of site-specific cancer during the first 5
years of treatment," researchers wrote in The Lancet.
"Fortification of flour and other cereal products involves
doses of folic acid that are, on average, an order of magnitude
smaller than the doses used in these trials.
For the analysis, the researchers combined data from 13
separate trials that randomly assigned participants to daily
folic acid or a vitamin-free placebo and recorded who went on to
The studies included a total of close to 50,000 volunteers
who were followed for just over five years, on average.
During that time, 7.7 percent of people in the folic acid
groups, and 7.3 percent in the placebo groups, were diagnosed
with any kind of cancer, a difference that could have been due
to chance, researchers said.
Likewise, there was no increased risk of individual cancers
- including colon, prostate, lung or breast cancer - attributed
to folic acid.
Most trials used daily doses of folic acid between 0.5 and 5
milligrams. In the one study that used a much larger dose, 40 mg
daily, there was still no difference in cancer diagnoses.
The total daily amount of folic acid through flour
fortification is less than 0.5 mg a day for most in the United
States. Folic acid is also naturally found in spinach,
asparagus, lettuce and other greens, with a recommended daily
upper limit of 1.0 mg.
"The conclusion you can make from this is that over a
relatively short period of time, there was no significant
benefit or harm," said John Baron from the Geisel School of
Medicine at Dartmouth in Lebanon, new Hampshire, who worked on
Most cancers take 10 to 20 years to develop, so it's hard to
tell from shorter studies like this one if there really is no
link or if the researchers didn't follow people for long enough
to see an association, whether positive or negative, he added.
The researchers agreed that the study shouldn't be the last
work on the potential side effects of folic acid.
For now, said nutrition researcher Joshua Miller of Rutgers
University in New Jersey, people might want to avoid piling
supplements on top of multivitamins and fortified food.
"People should realize if they're eating breakfast cereals
and bread and pastas, they're getting a good amount of folic
acid in food," he said. "I think they should try not to exceed
the upper limit."
(Reporting from New York by Genevra Pittman at Reuters Health;
editing by Elaine Lies)