Fish Oil Slashed Heart Attacks by 43% in Dialysis Patients

Patients on hemodialysis die from cardiovascular disease at 10 to 20 times the rate of the general population. Statins — the drugs that save millions of lives elsewhere — have failed repeatedly in this group. Multiple large trials ended at zero. Nephrologists had almost nothing to offer beyond blood pressure management and dialysis adjustments.

Then, at the American Society of Nephrology’s Kidney Week in late 2025, a number silenced the room. Four grams of fish oil per day. A 43% reduction in heart attacks, strokes, and cardiac death. Hazard ratio: 0.57. Published in the New England Journal of Medicine. Steven Nissen, the cardiologist who ran a competing trial, admitted: «I’m dumbfounded. Nothing has ever produced anything like this.»

1,228 Patients, Two Countries, Three and a Half Years

The PISCES trial (Protection against Incidences of Serious Cardiovascular Events Study) enrolled patients between 2013 and 2019 across 16 centers in Canada and Australia. A total of 1,228 people on maintenance hemodialysis were randomly assigned to receive either fish oil capsules (4 grams daily, containing 1.6 g EPA and 0.8 g DHA) or corn oil as a placebo. Average age: 64. Sixty-two percent male. One-third had already suffered a cardiovascular event.

EPA and DHA (eicosapentaenoic acid and docosahexaenoic acid) — the two principal omega-3 fatty acids found in fish oil. EPA primarily affects inflammation and clot formation; DHA is a major structural component of cell membranes.

The primary endpoint was hard events: cardiac death, myocardial infarction, stroke, and amputation from peripheral vascular disease. Not surrogate markers like cholesterol. Real people, real catastrophes.

Numbers That Stunned Cardiologists

In the fish oil group: 0.31 events per 1,000 patient-days. In the placebo group: 0.61. Hazard ratio: 0.57 (95% CI 0.47–0.70, p < 0.001).

Hazard ratio (HR) — a measure comparing the rate of events in two groups over time. HR = 0.57 means events occurred 43% less frequently in the treatment group than in the control group.

Every component of the composite endpoint fell significantly. Cardiac death: down 45%. Heart attack: down 44%. Amputation: down 43%. Stroke: down 63%. The expanded endpoint — including death from any cause — also favored fish oil (HR 0.77).

A counterintuitive finding: bleeding events were actually lower in the fish oil group — 4,8% versus 7,6% on placebo. Fish oil is widely assumed to thin the blood, but PISCES did not confirm that concern.

Why Dialysis Patients Specifically

Hemodialysis passes a patient’s entire blood volume through an external filter every two to three days. It keeps people alive when kidneys fail, but triggers a cascade of damage: chronic inflammation, oxidative stress, disrupted lipid metabolism. Standard cardiovascular risk factors (high LDL cholesterol) are paradoxically low in dialysis patients — non-traditional mechanisms do the killing.

One more detail: dialysis patients have some of the lowest circulating EPA and DHA levels in the medical literature. Uremia disrupts the conversion of plant-based omega-3 into active forms. Dietary restrictions on phosphorus and potassium leave little room for fish. Lead investigator Charmaine Lok hypothesizes that this extreme deficiency explains the magnitude of the effect: when the baseline is rock-bottom, supplementation produces the biggest gain.

Uremia — accumulation of toxins in the blood due to kidney failure. It drives inflammation, vascular damage, and disrupts fatty acid metabolism.

Twenty Years of Omega-3 Controversy

PISCES does not exist in a vacuum. Omega-3 is one of the most studied — and most contested — supplements in cardiology.

In 2018, the REDUCE-IT trial showed that high-dose pure EPA cut cardiovascular events by 25% in statin-treated patients with elevated triglycerides. Critics accused the investigators of using a mineral oil placebo that itself raised inflammatory markers, artificially inflating the apparent benefit.

In 2020, the STRENGTH trial used corn oil as placebo (the same as PISCES) and an EPA+DHA blend (the same as PISCES). Result: zero benefit. The trial was stopped early. STRENGTH’s principal investigator, Steven Nissen of the Cleveland Clinic, declared the debate settled.

Then PISCES arrived — same placebo, same type of omega-3 — with a hazard ratio of 0.57. This undermines Nissen’s argument that REDUCE-IT’s results were an artifact of harmful placebo. The difference lies in the population.

Trial	Drug	N	Population	Placebo	Result
REDUCE-IT	Pure EPA 4 g	8,179	Statins + ↑TG	Mineral oil	−25%
STRENGTH	EPA+DHA 4 g	13,086	Statins + ↑TG	Corn oil	0%
VITAL	EPA+DHA 1 g	25,871	Primary prevention	Olive oil	0%
PISCES	EPA+DHA 4 g	1,228	Hemodialysis	Corn oil	−43%

The pattern is visible: where the baseline omega-3 deficit is greatest — dialysis patients — replenishment produces the largest effect. Where people already get adequate fatty acids from food, the effect approaches zero.

What the Skeptics Say

The study was published in the New England Journal of Medicine and has undergone peer review, though the scientific community urges caution.

Nissen called the results «implausibly good»: «I’ve never seen a hazard ratio of 0.57 with any therapy — the most powerful statin and the most powerful PCSK9 inhibitor don’t produce that.» The NEJM editorialists (Mc Causland and Charytan of Brigham and Women’s Hospital) warned: «Contemporary medicine is replete with examples in which potentially practice-changing, outsized results of early trials have failed to be replicated.»

The primary target of criticism is the trial design. PISCES was open-label: after randomization, neither patients nor clinicians were blinded. This creates potential for bias in behavior and reporting. The trial did not measure inflammatory biomarkers (CRP, IL-6), leaving the mechanism opaque. There was no subanalysis by dialysis vintage. And results come from only Canada and Australia — populations with specific genetic and dietary profiles.

Still, the confidence interval (0.47–0.70) clears unity by a wide margin. The NNT — number needed to treat to prevent one event — is roughly 7 to 10. For comparison, statin NNT in primary prevention runs 50 to 100. If this result replicates, fish oil would rank among the most effective cardiovascular interventions available for this population.

Should You Rush to Buy Fish Oil?

For the 3.5 million people worldwide on hemodialysis, PISCES is the first positive news in years. Lok argues for immediate practice change. Nissen demands replication. The truth likely sits between: the result is too strong to ignore and too unusual to accept without caveats.

For healthy people, the takeaway is far more restrained. VITAL, the largest omega-3 trial in 25,871 healthy participants, found no significant reduction in cardiac events at a dose of 1 gram per day. PISCES worked in a unique population with extreme deficiency. «I don’t know that you would have the same effect if you just bought something over the counter, ” Lok herself cautions. The dose was high. The formulation was pharmaceutical-grade. A standard drugstore fish oil capsule contains 300–500 mg of omega-3. PISCES patients received 2,400 mg.

Fish oil is not a new drug. But PISCES is a reminder that context changes everything: the same molecule can be useless for one person and life-saving for another.

Frequently Asked Questions

Does this mean everyone should take fish oil?

No. PISCES studied hemodialysis patients — a group with extremely low omega-3 levels and catastrophic cardiovascular risk. The largest trial in healthy adults (VITAL, 25,871 participants) showed no significant reduction in cardiac events at the standard 1 g/day dose.

What dose was used?

Four grams of fish oil daily, delivering 1.6 g EPA and 0.8 g DHA — about 5 to 8 times more omega-3 than a standard over-the-counter capsule. The lead investigator explicitly stated that results from drugstore supplements may differ.

Why was the effect so large in dialysis patients?

Dialysis patients have some of the lowest circulating EPA and DHA levels ever documented. Uremia impairs omega-3 metabolism, and dietary restrictions limit fish intake. When the baseline is at rock-bottom, supplementation delivers the maximum impact — like watering a parched plant versus one that is already moist.

Doesn’t fish oil thin the blood dangerously?

Paradoxically, the PISCES fish oil group had fewer bleeding events (4.8% vs 7,6%). This is counterintuitive and needs further study. If you take anticoagulants, always consult your physician before adding high-dose omega-3.

When will a confirmatory trial happen?

As of March 2026, no replication study has been announced. Given the scale of the debate and the NEJM response, major nephrology centers are likely to begin planning within months.