Increased fish oil (omega-3 fatty acids [FA]) intake has been associated with reduced cardiovascular (CV) risk and based on trials conducted in the 1980s and 1990s, omega-3 FA supplements are recommended for secondary prevention. For primary prevention, increased fish intake is recommended. However, randomized trials conducted have not confirmed the CV benefits of omega-3 FA in patients with diabetes mellitus. The Study of Cardiovascular Events iN Diabetes (ASCEND) investigated whether omega-3 FA can reduce the risk of CV events and deaths in patients with diabetes without known arterial disease.

The placebo-controlled ASCEND-trial randomized 15,480 patients with diabetes (T1DM and T2DM) but without evidence of atherosclerotic cardiovascular disease, aged ≥40 years to receive 1-g capsules containing either n−3 fatty acids (fatty acid group) or matching placebo (olive oil) daily; in a separate portion of the trial, patients were also assigned to receive 100 mg of aspirin or matching placebo once daily. Using streamlined methods with mail-based questionnaires, over 99% completion for morbidity and mortality was achieved over a mean follow-up of 7.4 years.

Average adherence to omega-3 capsules was 77%. Similar effects on serious vascular event (SVE) were observed with omega-3 FA supplements and placebo (8.9% vs. 9.2%, HR: 0.97, 95%CI: 0.87-1.08, P=0.55). Omega-3 FA supplements did not have different effects on SVE or revascularization in different subgroups of patients, based on sex, BMI or 5-year vascular risk, compared to placebo. Death from any cause occurred in 9.7% of the patients in the fatty acid group and in 10.2% of the patients in the placebo group (rate ratio, 0.95; 95% CI, 0.86 to 1.05). There were no significant between-group differences in the rates of nonfatal serious adverse events.

The results show that omega-3 FA intake is safe, but does not result in beneficial effects on SVE, nor on all-cause or cause-specific mortality in patients with diabetes. Data thus suggest that the current guidelines on omega-3 FA intake should be reconsidered; to date, there does not seem to be any justification to take omega-3 FA supplements for CV disease prevention.

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