Large population studies consistently link fishy diets to better heart health.

However, such studies cannot prove a cause-and-effect relationship between a food or nutrient and a health condition.

While the outcomes of clinical trials testing omega-3 fish oil for heart health have varied, the overall picture has been positive.

That picture brightened after publication of two recent trials: see Omega-3s Score 2nd Big Heart Win and Omega-3s’ Heart Value Vindicated in Long, Large Clinical Trial.

Most clinical trials testing fish oil for heart health have looked for reductions in major adverse events like heart attacks and stroke, and reductions in deaths related to heart disease.

Less attention has been paid to the effects of fishy diets or omega-3 fish oil on heart failure, but the results have been generally positive: see Female Heart Failure Cut by Fish, Fatty Fish May Cut Men's Heart-Failure Risk, Heart Failure Findings Favor Omega-3s over Statin Drug, and Fish Oil May Help Congestive Heart Failure Patients.

And the recently published results of a well-designed population (epidemiological) study add significant evidence that fish oil can help prevent or ease heart failure.

Before we get to the results of that new study, let’s review what’s meant by “heart failure”, and what’s known about the effects of omega-3 fatty acids on this condition.

What is heart failure?
The term “heart failure” simply means that the heart isn’t pumping strongly enough to push oxygen and nutrient-rich blood throughout the body, while “congestive heart failure” means a degree of heart failure that demands quick medical attention.

The weak pumping action that defines heart failure causes fatigue and shortness of breath and may induce coughing, which combine to make exercise and even everyday activities difficult to near-impossible.

Heart failure (HF) affects some 5.7 million Americans, and — even with treatment — about half of people diagnosed with HF die within five years.

Unfortunately, the HF death rate hasn’t fallen in recent years, highlighting, as the authors of a recent evidence review wrote, “… the need for new therapeutic options”. (O'Connell TD et al. 2017)

They also stressed that the wide design variations among, and weaknesses of, many clinical trials have misled people — and many doctors — about the value of omega-3s for heart health.

(Clinical trials that haven't found benefits from omega-3 fish oil typically used low doses and/or involved seriously sick heart patients who were also on standard drug therapies like statins, to which omega-3s can't be expected to add big additional benefits.)

Several co-authors of the new study previously conducted a mouse study showing that high doses of omega-3s helped preserve the animals’ heart-pumping function in the face of artificially induced hypertension — a finding that helped prompt the new study (Chen J et al. 2011).

Large study adds to the evidence favoring fish oil for heart failure
The findings stem from an analysis of blood tests and health outcomes from participants in the Multi-Ethnic Study of Atherosclerosis (MESA).

The study was led by scientists from the University of Rochester School of Medicine and included researchers from Wake Forest University, Pennsylvania State University, and the University of Minnesota (Block RC et al. 2019).

As the authors of the new research paper wrote, “This study is the first to determine the ability of [omega-3 blood levels] to predict heart failure outcomes in white, African American, Asian, and Hispanic populations.”

The 6,814 volunteers were 45 to 84 years old when they were recruited from six American communities between 2000 and 2002, and each participant was followed for an average of 13 years.

Out of the total, 6,562 volunteers had their blood tested for omega-3 levels at the outset of the study. In addition, almost all the participants were visited at the outset of the study and again about every other year.

Physicians used medical records to place participants into one of four categories. People judged to suffer from heart failure were also categorized by the percentage of blood pumped out by the left heart ventricle (chamber) — a measure called ejection fraction or EF:

  1. People free of heart failure
  2. People with heart failure but and unmeasured ejection fraction
  3. Heart failure with reduced ejection fraction (HFrEF) or systolic heart failure. The heart muscle doesn’t contract effectively and pumps less blood.
  4. Heart failure with preserved ejection fraction (HFpEF) or diastolic heart failure. The heart muscle contracts normally but the heart's chambers (ventricles) don’t relax enough between contractions.

During the average 13 years of follow-up, 292 participants developed heart failure: 128 developed HFrEF, 110 developed HFpEF, and 54 had an unknown EF status.

The results of the researchers’ analysis were clear: higher blood levels of omega-3 EPA or combined omega-3 EPA + DHA were linked to significantly reduced risks for having or developing heart failure.

Despite an odd emphasis on EPA in the study itself and in media reports about it — the risk reduction was greatest for people with higher blood levels of EPA + DHA, versus higher blood levels of EPA alone.

The authors stressed the ease and safety of using their findings to reduce the risk for heart failure: “Given that [omega-3 blood levels] can be increased by the ingestion of seafood or fish oil capsules [which is] safe and relatively inexpensive, this preventive measure is … quite feasible.”

Most participants had inadequate omega-3 blood levels
Judging by related animal research, most of the new study's participants (75.5%) had insufficient or marginal EPA blood levels at its outset:

  • 73.1% had insufficient levels
  • 2.4% had marginal levels
  • 4.5% had sufficient levels

Hispanic and black participants had the lowest EPA levels, with white and Chinese volunteers showing higher levels.

Blood levels of EPA are pretty good predictors of DHA levels, because most fish and fish oils contain roughly equivalent amounts of both fatty acids — although most fish and fish oils contain somewhat more EPA than DHA. 

Accordingly, people who eat more fish than most of their peers — and/or who take fish oil supplements — usually have higher blood levels of both EPA and DHA.

The predominance of EPA over DHA in most fish and fish oils seems beneficial, because the body converts EPA to DHA much more easily than it can convert DHA to EPA, and both are essential to human health.

Versus EPA, omega-3 DHA plays a greater role in brain health, so if you're striving to maintain healthy memory and thinking abilities, it may make sense to take a high-DHA supplement in addition to a standard, roughly balanced EPA-DHA fish or krill oil.

Conversely, omega-3 EPA is more closely associated with mood health, so if that's your goal, it makes sense to take a high-EPA supplement in addition to a standard fish oil.


  • Block RC, Liu L, Herrington DM, Huang S, Tsai MY, O'Connell TD, Shearer GC. Predicting Risk for Incident Heart Failure With Omega-3 Fatty Acids: From MESA. JACC Heart Fail. 2019 Jul 3. pii: S2213-1779(19)30217-3. doi: 10.1016/j.jchf.2019.03.008. [Epub ahead of print]
  • Chen J, Shearer GC, Chen Q, Healy CL, Beyer AJ, Nareddy VB, Gerdes AM, Harris WS, O'Connell TD, Wang D. Omega-3 fatty acids prevent pressure overload-induced cardiac fibrosis through activation of cyclic GMP/protein kinase G signaling in cardiac fibroblasts. Circulation. 2011 Feb 15;123(6):584-93. doi: 10.1161/CIRCULATIONAHA.110.971853. Epub 2011 Jan 31.
  • O'Connell TD, Block RC, Huang SP, Shearer GC. ω3-Polyunsaturated fatty acids for heart failure: Effects of dose on efficacy and novel signaling through free fatty acid receptor 4. J Mol Cell Cardiol. 2017 Feb;103:74-92. doi: 10.1016/j.yjmcc.2016.12.003. Epub 2016 Dec 14. Review.