Marine Omega-3 Fatty Acid Supplementation and Cancer Risk


Key Points

  • Use of n-3 fatty acid supplementation did not reduce the risk for invasive cancer vs placebo over 5 years.
  • No difference in death from cancer was observed over 5 years.

In a trial reported in The New England Journal of Medicine by Manson et al, marine n-3 (omega-3) fatty acid supplementation was found to have no benefit in reducing the risk for invasive cancer vs placebo over 5 years of follow-up. Higher intake of n-3 fatty acids has been associated with a reduced risk for cancer in observational studies.

Study Details

The trial was a randomized, placebo-controlled trial, with a 2-by-2 factorial design, of vitamin D3 and marine n-3 fatty acids in the primary prevention of cardiovascular disease and cancer among men 50 years of age or older and women 55 years of age or older.

A total of 25,871 participants were randomly assigned between November 2011 and March 2014 to receive n-3 fatty acid supplementation at 1 g/d as a fish oil capsule (n = 12,933) or placebo (n = 12,938). The fish oil capsule contained 460 mg of eicosapentaenoic acid (EPA) and 380 mg of docosahexaenoic acid (DHA).

The primary endpoint was the incidence of invasive cancer of any type.

Risk of Cancer

The median follow-up was 5.3 years. Invasive cancer was diagnosed in 820 participants in the n-3 group vs 797 in the placebo group (hazard ratio [HR] = 1.03, P = .56). No significant differences between groups were observed in the incidence of breast cancer (117 vs 129 participants, HR = 0.90, 95% confidence interval [CI] = 0.70–1.16), prostate cancer (219 vs 192, HR = 1.15, 95% CI = 0.94–1.39), or colorectal cancer (54 vs 44, HR = 1.23, 95% CI = 0.83–1.83). Death from cancer occurred in 168 vs 173 participants (HR = 0.97, 95% CI = 0.79–1.20).

In a post hoc analysis excluding the first 2 years of follow-up, there were no significant differences in the incidence of invasive cancer of any type (536 vs 476, HR = 1.13, 95% CI = 1.00–1.28) or death from cancer (126 vs 135, HR = 0.93, 95% CI = 0.73–1.19). With regard to cardiovascular endpoints, there were no differences in the incidence of major cardiovascular events (HR = 0.92, P = .24) or death from cardiovascular causes (HR = 0.96, 95% CI = 0.76–1.21).

The investigators concluded, “Supplementation with n-3 fatty acids did not result in a lower incidence of major cardiovascular events or cancer than placebo.”

The study was funded by the National Institutes of Health and others.

Disclosure: See the study authors’ full disclosures at

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.