Meta-analysis: antioxidant supplements for primary and secondary prevention of colorectal adenoma.
BACKGROUND
Colorectal cancer may be prevented by reducing the development of adenomatous polyps.


OBJECTIVE
To assess the benefits and harms of antioxidant supplements in preventing colorectal adenoma.


METHODS
Using the Cochrane Collaboration methodology we reviewed all randomized clinical trials comparing antioxidant supplements with placebo or no intervention. We searched electronic databases and the reference lists until October 2005. Outcome measures were development of colorectal adenoma adverse events. We analysed dichotomous outcomes with fixed- and random-effects model meta-analyses and calculated the relative risk with 95% confidence interval.


RESULTS
We identified eight randomized trials (17 620 participants). Neither fixed-effect (relative risk: 0.93, 95% CI: 0.81-1.1) nor random-effect model meta-analyses (0.82, 0.60-1.1) showed statistically significant effects of supplementation with beta-carotene, vitamins A, C, E and selenium alone or in combination. Antioxidant supplements seemed to increase the development of colorectal adenoma in three low-bias risk trials (1.2, 0.99-1.4) and significantly decrease its development in five high-bias risk trials (0.59, 0.47-0.74). The estimates difference is significant (P < 0.0001). There was no significant difference between the intervention groups regarding adverse events, including mortality (0.82, 0.47-1.4).


CONCLUSIONS
We found no convincing evidence that antioxidant supplements have significant beneficial effect on primary or secondary prevention of colorectal adenoma.
Bjelakovic
G
G
The Cochrane Hepato-Biliary Group, Copenhagen Trial Unit, Centre for Clinical Intervention Research, Copenhagen University Hospital, H:S Rigshospitalet, Copenhagen, Denmark. goranb@junis.ni.ac.yu
Nagorni
A
A
Nikolova
D
D
Simonetti
R G
RG
Bjelakovic
M
M
Gluud
C
C
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000975:Antioxidants / Q000627:therapeutic use*; D015179:Colorectal Neoplasms / Q000178:diet therapy / Q000517:prevention & control*; D019587:Dietary Supplements; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016032:Randomized Controlled Trials as Topic; D016896:Treatment Outcome
D000975:Antioxidants