Excess Folic
Acid May Raise Cancer Risk
Where a little may be good, a lot may be hazardous... such may
be the case with folate, and its synthetic form folic acid, the B
vitamin that helps protect the nervous system and prevent anemia.
For years now, the US government (along with Canada and Chile) has
required that most breads, flours, cornmeal, rice and some other
grains be fortified with folic acid as a way to reduce birth
defects known to be caused by folate deficiency.
It’s working -- incidence of neural tube birth defects has been
reduced by as much as 50% in these countries, but at the same time,
there has been another, totally unexpected development. All three
countries have also seen rates of colorectal cancer rise, an abrupt
reversal after years of decline -- with the increase estimated at
an additional four to six cases of colorectal cancer per 100,000
people. Adding to that concern were the results of a large clinical
trial published in the Journal of the American Medical
Association in 2007 concerning folic acid supplementation
and colon cancer. The participants, all of whom had previously had
colon polyps, were divided into two groups -- one group took 1,000
mcg daily (this is considered the uppermost safe limit and exceeds
the daily recommended intake, which is 400 mcg) of folic acid and
the other a placebo. After seven years, the study found that those
taking supplemental folic acid were more likely to have multiple
polyps, and at higher risk, than those who didn’t take
it. Even more troubling: A follow-up study of
this same group found that after 10 or 11 years, those
supplementing with folic acid had a three-fold increase in prostate
cancer compared with the group on placebo.
TRADING ONE PROBLEM FOR ANOTHER?
Joel Mason, MD, director of the Vitamins and Carcinogenesis
Laboratory at the Jean Mayer USDA Human Nutrition Research Center
on Aging at Tufts University, is author of a recent report on this
topic in Nutrition Reviews. He told me the report
generated controversy because folate fortification has so
effectively reduced birth defects -- but his intent, however, was
not to be "anti-fortification," but rather to generate dialogue
about a potential risk for one group of people in spite of the
clear benefits for another at a time when many countries are
considering fortification.
Paradoxically, there is sound evidence that folate, which has a
pivotal role in DNA synthesis,
protects against colorectal cancer. Dr. Mason
speculated that perhaps its very function of helping create DNA for
new cells means that when ingested in large quantities, folate
stimulates the growth of existing cancerous or precancerous cells
that would otherwise remain stable. Another possibility relates to
the fact that folic acid, rather than folate itself, is used to
fortify foods because it is cheaper and also more stable. The body
must convert folic acid into folate, he says, and ingesting an
excessive amount of folic acid may overwhelm the conversion system,
leaving a reservoir of synthetic folate that could have detrimental
effects. Current research is exploring whether folic acid itself is
cancer-promoting, but there’s little evidence of this Dr. Mason
said, so he believes it’s more likely related to excessive intake
of the vitamin, regardless of its form.
A FOLIC ACID MEASURE
In no way does this diminish the importance of an abundance of
folate, says Dr. Mason, describing it as "healthful and in no way
harmful." Dietary folate is available in a variety of foods,
including dark green leafy vegetables, legumes, citrus fruits and
berries.
And folic acid, for the most part, also is healthful and
relatively few people are at risk for getting too much. Dr. Mason
says supplementation adds a "fairly modest amount" to typical
intake, about 100 mcg to 200 mcg per day. He noted that the
situation only gets worrisome for those who routinely exceed 1 mg a
day (1,000 mcg) of folic acid through supplementation in a variety
of forms. This would describe a person who takes a multivitamin
(400 mcg of folic acid), a B complex (another 400 mcg), and then
eats fortified breakfast cereal (typically containing 100 to 400
mcg). It’s still morning and we already are at the ceiling of 1,000
mcg folic acid -- but then for lunch there is a sandwich with
fortified bread (50 to 120 mcg for two slices), maybe a pasta
dinner (another 100 to 200 mcg) and the total is nearly 1,400 mcg,
clearly topping the upper limit of safety. For those who snack on
vitamin-packed energy bars and sip vitamin-infused water all day,
the folic acid intake goes even higher.
There isn’t enough data yet to make an absolute statement about
folic acid intake, but the current recommendation regarding the
uppermost safe intake level (1,000 mcg/day) continues to be an
excellent guideline, Dr. Mason said. Vitamin labels clearly
identify how much folic acid they contain, but it’s harder to
figure out how much is in fortified foods. The law says that all
wheat flour, rice and several other uncooked cereal grains labeled
as "fortified" must have added folic acid... but there are a few
nonfortified examples of these foods on the market. You can look
for these, but it might be easier to just be aware of how much
folic acid you are ingesting in vitamin supplements, because these
appear to be the major source of excessive intake.
Source(s):
Joel Mason, MD, director of the Vitamins and Carcinogenesis
Laboratory at the Jean Mayer USDA Human Nutrition Research Center
on Aging at Tufts University, Boston.