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Nutrition, Vitamins & Supplements for Seniors
Folic Acid Supplements Do Not Appear to Reduce Risk
of Colorectal Tumors
Previous studies found folate may help prevent
colorectal tumors
 June
6, 2007 - New research indicates that folic acid supplementation does
not decrease the risk of benign colorectal tumors, but may possibly
increase the risk for some type of colorectal tumors, according to a
study in the June 6 issue of the Journal of the American Medical
Association. Previous studies have suggested that folate supplementation
may help to prevent colorectal tumors.
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Bernard F. Cole, Ph.D., of Dartmouth Medical
School, Hanover, N.H., and colleagues evaluated the effect of folate for
the prevention of new colorectal adenomas (benign tumors, precursors of
most colorectal cancers) in persons with a history of these types of
lesions.
The trial was conducted at nine clinical centers
between July 1994 and October 2004 and included 1,021 men and women with
a recent history of colorectal adenomas but no previous large intestine
cancerous tumor.
Participants were randomly assigned to receive 1
mg/day of folic acid (516) or placebo (505), and were separately
randomized to receive aspirin (81 or 325 mg/day) or placebo. Follow-up
consisted of two colonoscopic examination cycles (the first interval was
at 3 years and the second at 3 or 5 years later).
In the first follow-up interval, adenomas occurred
in 42.4 percent of the participants in the placebo group and 44.1
percent of the participants in the folic acid group. In the second
follow-up interval, adenomas occurred in 37.2 percent of the
participants in the placebo group and 41.9 percent of the participants
in the folic acid group.
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Watch Video |
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June 6,
2007 - Colon polyps can sometimes turn into cancer. Some studies
have hinted that taking large amounts of a vitamin called folic
acid could help prevent colon polyps. But a new study says
taking high-dose folic acid supplements does not reduce the risk
of colon polyps, and may even increase the risk. Mavis Prall
explains in this weeks JAMA Report.
Click for Windows Video. |
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In both follow-up intervals, participants in the
folic acid group tended to have higher rates of advanced adenomas and
multiple adenomas.
In the first follow-up interval, advanced lesions
occurred in 8.6 percent of the participants in the placebo group and
11.4 percent of the participants in the folic acid group.
The respective numbers in the second follow-up
interval were 6.9 percent and 11.6 percent for both groups, a 67 percent
(but non-statistically significant) increased risk of advanced lesions.
Participants in the folic acid group (30 individuals, 9.9 percent) had
more than twice the risk of having three or more adenomas than those in
the placebo group (13 individuals, 4.3 percent).
In conclusion, our study indicates that folate,
when administered as folic acid for up to 6 years, does not decrease the
risk of adenoma formation in the large intestine among individuals with
previously removed adenomas.
"The evidence for an increased risk of adenomas is
equivocal and requires further research. In view of the fortification of
the U.S. food supply with folate, and some suggestions that folate could
conceivably increase the risk of neoplasia even outside the colorectum,
this line of investigation should have a high priority, the authors
write.
Editorial: Folate and CancerTiming Is
Everything
In an accompanying editorial, Cornelia M. Ulrich,
M.S., Ph.D., and John D. Potter, M.D., Ph.D., of the Fred Hutchinson
Cancer Research Center, Seattle, discuss the findings of Cole and
colleagues.
How should the unexpected results of this study be
interpreted? The most likely explanation for the increased risk of
advanced and multiple adenomas in the intervention group is that
undetected early precursor lesions were present in the mucosa [a type of
membrane] of these patients (who are at increased adenoma risk), and
that folic acid promoted growth of these lesions.
"This hypothesis is consistent with experimental
studies showing increased colorectal neoplasia when folic acid is
administered after lesions are present.
Nonetheless, by the nature of the design, the
results do not provide information on primary prevention by folic acid
(the potential for folic acid to reduce the incidence of first
adenomas). The question of efficacy of folate in cancer prevention is
not resolved, and animal experiments showing chemopreventive effects of
folate, as well as the strong observational epidemiological evidence,
speak to the potential of folate as a chemopreventive agent, if taken
early.
"Unfortunately, primary prevention trials that
start in childhood would be lengthy, expensive, and logistically nearly
impossible.
The results of the clinical trial by Cole et al
illustrate, yet again, the principle that chemoprevention with single
agents is problematic. Similar to the increased risk of lung cancer
observed with beta carotene supplementation, selection of resistant
clones is as plausible an outcome of the use of single-agent
chemoprevention as it is of single-agent chemotherapy, they write.
It is time to be as thoughtful about the need for
multiagent chemoprevention, not forgetting that diet is one version of
this, as about the use of multiagent chemotherapy.
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