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Effects of Omega-3 Fatty Acids on
Cancer Risk. A Systematic Review
Catherine H. MacLean,
MD, PhD; Sydne J. Newberry, PhD;
Walter A. Mojica, MD, MPH; Puja Khanna, MD; Amalia
M. Issa, MPH, PhD; Marika J. Suttorp, MS; Yee-Wee
Lim, MD, PhD; Shana B. Traina, MA; Lara
Hilton, BA; Rena Garland, BA; Sally C.
Morton, PhD
Author Affiliations: Southern
California Evidence-Based Practice Center, which includes RAND Health,
Santa Monica (Drs MacLean, Newberry, Mojica, Lim, and Morton and Mss
Suttorp, Hilton, and Garland), the Greater Los Angeles VA Healthcare
System, Los Angeles (Dr MacLean), and the University of California Los
Angeles School of Public Health, Los Angeles (Dr Issa and Ms Traina);
and Wright State University School of Medicine, Dayton, Ohio (Dr
Khanna).
Context.
Omega-3 fatty acids are purported to reduce the risk of
cancer.
Studies have reported mixed results.
Objective.
To synthesize published and unpublished evidence to
determine estimates of the effect of omega-3 fatty acids on
cancer risk in prospective cohort studies.
Data Sources.
Articles published from 1966 to October 2005 identified
through MEDLINE, PREMEDLINE, EMBASE, Cochrane Central Register
of Controlled Trials, and CAB Health; unpublished literature sought
through letters to experts in the neutraceutical industry.
Study Selection.
A total of 38 articles with a description of effects of
consumption of omega-3 fatty acids on tumor incidence, prospective
cohort study design, human study population; and description
of effect of omega-3 among groups with different levels of
exposure in the cohort were included.
Two reviewers independently reviewed articles using
structured abstraction forms; disagreements were resolved
by consensus.
Data Extraction.
Two reviewers independently abstracted detailed data about
the incidence of cancer, the type of cancer, the number and
characteristics of the patients, details on the exposure to
omega-3 fatty acids, and the elapsed time between the
intervention and outcome measurements.
Data about the methodological quality of the study were
also abstracted.
Data Synthesis.
Across 20 cohorts from 7 countries for 11 different types
of cancer and using up to 6 different ways to categorize
omega-3 fatty acid consumption, 65 estimates of the
association between omega-3 fatty acid consumption were reported.
Among these, only 8 were statistically significant.
The high degree of heterogeneity across these studies precluded pooling
of data.
For breast cancer 1 significant estimate was for increased
risk (incidence risk ratio [IRR], 1.47; 95% confidence interval
[CI], 1.10-1.98) and 3 were for decreased risk (RR, 0.68-0.72);
7 other estimates did not show a significant association.
For colorectal cancer, there was 1 estimate of decreased risk (RR,
0.49; 95% CI, 0.27-0.89) and 17 estimates without association.
For lung cancer one of the significant associations was for increased
cancer risk (IRR, 3.0; 95% CI, 1.2-7.3), the other was for
decreased risk (RR, 0.32; 95% CI, 0.13-0.76), and 4 other
estimates were not significant.
For prostate cancer, there was 1 estimate of decreased risk
(RR, 0.43; 95% CI, 0.22-0.83) and 1 of increased risk (RR,
1.98; 95% CI, 1.34-2.93) for advanced prostate cancer; 15
other estimates did not show a significant association.
The study that assessed skin cancer found an increased risk
(RR, 1.13; 95% CI, 1.01-1.27).
No significant associations between omega-3 fatty acid
consumption and cancer incidence were found for
aerodigestive cancer, bladder cancer, lymphoma, ovarian
cancer, pancreatic cancer, or stomach cancer.
Conclusions.
A large body of literature spanning numerous cohorts from
many countries and with different demographic characteristics does
not provide evidence to suggest a significant association between
omega-3 fatty acids and cancer incidence.
Dietary supplementation with omega-3 fatty acids is
unlikely to prevent cancer.
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