A study published in the New England Journal of Medicine made headlines suggesting that omega-3 supplements are ineffective in reducing cardiovascular events in people with diabetes. But a deeper dive into the ASCEND trial reveals a more complex and encouraging narrative—particularly for those considering omega-3s to support heart health.
What Was the ASCEND Study?
The ASCEND trial—A Study of Cardiovascular Events iN Diabetes—was a large randomized, placebo-controlled study involving more than 15,000 participants in the UK with diabetes but no known cardiovascular disease. From 2007 to 2011, researchers evaluated whether 100 mg of aspirin and/or 1 gram of prescription omega-3s (containing 840 mg of EPA and DHA) daily could reduce the risk of major cardiovascular events and cancer.
Participants were followed for an average of seven years. The study compared the rates of serious cardiovascular events, such as heart attack, stroke, and vascular-related death, between those taking omega-3s and those receiving a placebo (olive oil).
The Surface-Level Conclusion
The trial reported that just under 9% of participants in the fish oil group experienced a cardiovascular event, compared to just over 9% in the placebo group. This difference was not statistically significant. As a result, the authors concluded that omega-3 supplements “do not reduce the risk of cardiovascular events in patients with diabetes.”
This headline-ready conclusion overshadowed a key statistically significant finding: omega-3 supplementation reduced the risk of vascular death by 18%.
The Significance of Reduced Vascular Death
Vascular death includes coronary death, stroke-related death, and other vascular causes. In the ASCEND trial, there were 196 vascular deaths in the omega-3 group and 240 in the placebo group—a statistically significant reduction of 18 percent.
This is a critical clinical outcome. It was part of the trial’s pre-defined primary endpoint, meaning it was not an incidental finding or secondary analysis. This benefit aligns with previous research showing omega-3s reduce the risk of cardiac death, including sudden cardiac events.
In fact, the study also reported a 21% reduction in coronary death in the omega-3 group, which narrowly missed statistical significance. Given that the study was not powered to detect such a difference, this result remains clinically relevant.
Why Baseline Omega-3 Status Matters
Dr. Bill Harris, founder of OmegaQuant and co-inventor of the Omega-3 Index, helped analyze fatty acid profiles in a subset of ASCEND participants. He noted a surprising and important detail: participants in this trial already had unusually high Omega-3 Index levels at baseline.
The intervention group, in particular, started with an average Omega-3 Index of 7%—already near the target range of 8–12% associated with cardiovascular protection. With supplementation, their Index increased to 9.1%. In contrast, the general UK population averages below 4%.
This presents a major limitation. When individuals already have high omega-3 levels, adding a modest supplement dose is unlikely to produce substantial additional benefits. As Dr. Harris put it, “It’s like conducting a statin trial in people who are already taking a statin. A small dose increase won’t yield dramatic results.”
The Pitfall of Low Dosing in Omega-3 Research
Another issue is the relatively low dose of omega-3s used. While the prescribed dose was 840 mg of EPA+DHA daily, only 77% of participants adhered to the protocol. As a result, the average intake was likely closer to 647 mg per day.
This is well below the dose used in other studies that demonstrated clear cardiovascular benefits. For instance, the REDUCE-IT trial used 4 grams of EPA daily and showed a 25% reduction in major cardiovascular events. By comparison, the ASCEND dose was modest and perhaps insufficient to generate robust changes in cardiovascular outcomes—especially in a population that was already omega-3 replete.
The Case for Omega-3 Index-Guided Trials
The ASCEND findings underscore the importance of screening participants for their baseline omega-3 status before beginning supplementation trials. Without this step, researchers risk studying participants who may not need supplementation in the first place.
Targeting individuals with low Omega-3 Index values (e.g., below 5%) could result in clearer, more meaningful outcomes and help establish optimal dosing strategies. It would also reflect real-world usage more accurately, as most consumers interested in omega-3 supplementation do not already have high baseline levels.
What This Means for You
While the ASCEND study was interpreted by some as a dismissal of fish oil’s value, it actually reinforces a more targeted and personalized approach to supplementation. The 18% reduction in vascular death is clinically important, and the study’s limitations highlight the need for more thoughtful research designs moving forward.
If you are living with diabetes or are concerned about heart health, testing your Omega-3 Index can help determine whether supplementation is appropriate for you. If your levels are low, increasing your intake of EPA and DHA through fish or high-quality supplements may offer meaningful cardiovascular protection.
Final Thoughts
The ASCEND study is not the final word on omega-3s and heart health. Rather, it adds to the growing body of evidence suggesting that omega-3 effectiveness depends greatly on the individual’s baseline status and the dosage used. For those with low omega-3 levels, the benefits may be substantial. As with many aspects of nutrition and health, personalization is key.
Before making any decisions, speak with your healthcare provider and consider getting your Omega-3 Index tested. It’s a simple step that could help you fine-tune your approach to heart health and get the most benefit from your omega-3 intake.
