Oct 7, 2013 - ... degree to which the findings of this study are likely to be free of bias. ... Kwak SM, Myung SK, Lee Y
The Bottom Line
October 7, 2013
Blood levels of omega-3 fatty acids
associated with slight increase in prostate cancer incidence. STRENGTH OF EVIDENCE: VERY LOW
Why is this important? Despite inconclusive evidence, omega-3 polyunsaturated fatty acids (PUFAs) are often heralded for health benefits including antiinflammatory properties. Prior studies have suggested that PUFAs might be associated with risk of prostate cancer.
Facts Participants were from SELECT, a clinical trial of an unrelated treatment for prostate cancer prevention, which was designed for a different purpose. 1 This was a sub-study of 834 men who developed prostate cancer and 1364 men who did not. 2 Baseline blood levels of a chemical marker of PUFA intake were tested in all participants. Plasma level of phospholipid fatty acids was higher in patients who developed prostate cancer, with the highest levels conferring the highest risk.
The
Harms and concerns: These data do not allow an accurate numerical or visual display of the magnitude of risk. This was an observational study, and therefore it can suggest possible associations, but not causation. The measurement of PUFAs was not perfectly reliable, and the clinical significance of the biomarkers is unclear. Consumption of omega-3 supplements was not assessed. The safety and benefit of PUFAs for other health reasons is controversial. Most notably, a long-believed benefit in preventing heart disease may be unfounded. PUFA intake for primary prevention of heart disease has been shown ineffective 3, 4. No specific recommendations about fish oil consumption can be made with certainty based on this study.
Bottom Line
In a preliminary study, the development of prostate cancer was associated with presence of higher blood levels of omega-3 fatty acids. These results are unlikely to inform practice regarding taking omega-3 supplements.
Strength of Evidence (Adapted from Guyatt G BMJ, 26 April 2008) This refers to the degree to which the findings of this study are likely to be free of bias. High Moderate Low Very low
Tips for Discussion of Results with Patients This study did not examine fish oil or other omega-3- containing supplements. It examined blood markers related to omega-3 ingestion. This was an observational study, which found associations between ω-3 PUFA and prostate cancer, but did not establish cause-and-effect relationships. If omega-3 fatty acids do affect development of prostate cancer, the magnitude of the effect is likely to be small. The decision to take Omega-3 fatty acids should include an understanding that there may be risks associated.
References 1.
Brasky TM, Darke AK et al. Plasma phospholipid fatty acids and prostate cancer risk in the SELECT trial. J Natl Cancer Inst. 2013; epub 1-10.
2.
Klein EA, Thompson IM et al. Vitamin E and Prostate Cancer: The Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. 2011; 306(14):1549-1556.
3.
The Risk and Prevention Study Collaborative Group. n–3 Fatty Acids in Patients with Multiple Cardiovascular Risk Factors N Engl J Med 2013; 368:1800-1808.
4.
Kwak SM, Myung SK, Lee YJ, Seo HG for the Korean Meta-analysis Study Group. Efficacy of Omega-3 Fatty Acid Supplements (Eicosapentaenoic Acid and Docosahexaenoic Acid) in the Secondary Prevention of Cardiovascular Disease: A Meta-analysis of Randomized, Double-blind, Placebo-Controlled Trials. Arch Intern Med. 2012;172(9):686-694.
Written by the Evidence-Based Medicine Task Force Daniella Zipkin MD
Zackary Berger, MD, PhD
Scott Kaatz, DO, MSc
Jeremy Sussman MD, MSc
Rebecca Beyth, MD, MSc
Deborah Korenstein, MD
KoKo Aung, MD, MPH
Daniel Elliott, MD, MSCE
M.E. Beth Smith, DO
The Bottom Line summaries reflect the expertise and opinions of the SGIM EBM Task Force as of the date of release of this summary.
October 7, 2013
The Bottom
Line
Blood levels of omega-3 fatty acids associated with slight increase in prostate cancer incidence.
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