Folic acid supplementation and colorectal cancer risk: a meta-analysis.
OBJECTIVE
This meta-analysis aims to determine the effect of folic acid supplementation on colorectal cancer risk.


METHODS
A structured search of the MEDLINE, EMBASE, Cochrane and CINAHL databases was undertaken in July 2008. All published full text English language articles were searched that included a randomized or pseudo-randomized comparison of subjects who received folate vs subjects who did not in relation to their risk of adenoma or advanced adenomatous lesions, including colorectal cancer. A weighted treatment effect (using fixed effects) was calculated across trials.


RESULTS
Overall, the risk of an adenomatous lesion was not increased (odds ratio 1.09, 95% confidence interval 0.93-1.28) among patients who received folate supplementation for up to 3 years; however, for those who received folate for over 3 years, the risk of an adenomatous lesion was increased (odds ratio 1.35, 95% confidence interval 1.06-1.70). The risk associated with treatment was the highest for the occurrence of an advanced lesion (odds ratio 1.50, 95% confidence interval 1.06-2.10). There was no significant statistical heterogeneity in the analyses.


CONCLUSIONS
At the 3-year colonoscopic follow up, folate supplementation had no effect on adenoma recurrence overall. While colonic surveillance beyond 3 years revealed an increased risk of colorectal adenoma, especially advanced adenoma, among those participants randomized to the folate group. This meta-analysis challenges the results from epidemiological studies that folate status is inversely related to the risk of developing colorectal cancer.
Colorectal Unit, Department of Surgery, Christchurch Hospital, New Zealand. frank.frizelle@cdhb.govt.nz
J
J
Fife
S
S
Raniga
P N
PN
Hider
F A
FA
Frizelle
D000236:Adenoma / Q000139:chemically induced*; D015179:Colorectal Neoplasms / Q000139:chemically induced; D019587:Dietary Supplements / Q000009:adverse effects*; D005492:Folic Acid / Q000008:administration & dosage / Q000009:adverse effects*; D006801:Humans; D013997:Time Factors
D005492:Folic Acid