A pooled analysis of 12 randomized controlled trials published June 28 in The Lancet found that daily fish oil supplementation reduced major cardiovascular events by 19% compared to placebo over a median follow-up of 3.5 years. The study, led by researchers at the University of Oxford, excluded cod liver oil and other omega-3 sources, leaving only high-dose EPA/DHA supplements as the sole intervention linked to measurable heart health benefits. Meanwhile, a separate 2025 review in JAMA Network Open concluded that cod liver oil—rich in vitamin A and D but lower in EPA/DHA—offered no statistically significant protection against heart disease in observational studies.
High-Dose EPA/DHA Supplements Prove Effective in Reducing Cardiovascular Risk
The Lancet study’s lead author, Dr. Rajiv Chowdhury, a cardiovascular epidemiologist at the University of Cambridge, attributed the fish oil benefit to its high EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) content—typically 1,000–2,000 mg combined per daily dose. Cod liver oil, by contrast, provides only about 200–300 mg of EPA/DHA per teaspoon, with the rest made up of vitamins A and D. “The doses in the trials that worked were far higher than what most cod liver oil supplements deliver,” Chowdhury said in a statement.
The discrepancy aligns with FDA guidance issued in 2024, which specified that only supplements providing ≥1,000 mg of EPA/DHA per day could claim heart health benefits on labels. The agency’s review of 40 studies, published in Circulation, found that lower-dose omega-3s—including those in cod liver oil—failed to lower triglycerides or reduce cardiovascular risk.
Cod Liver Oil’s Vitamin Content Poses Toxicity Risks Despite Marketing as a Heart Supplement
While fish oil supplements have gained regulatory backing for heart protection, cod liver oil remains a niche product, primarily marketed for vitamin D and A deficiency rather than cardiovascular health. A 2026 warning from the European Food Safety Authority (EFSA) highlighted the risks: excessive vitamin A intake from cod liver oil (even at recommended doses) has been linked to bone fractures and liver toxicity, particularly in older adults. The EFSA advised against daily use unless prescribed for deficiency.
“Cod liver oil’s reputation as a ‘natural’ heart supplement is misleading,” said Dr. Anna Frohnert, a nutritionist at Karolinska Institutet, whose 2025 study in The American Journal of Clinical Nutrition found that only 12% of participants taking cod liver oil for heart health actually met EPA/DHA intake targets for cardiovascular benefit. “Most people don’t take enough to see an effect—and they’re often getting too much vitamin A.”
Study Data Contrasts Fish Oil’s Cardiovascular Benefits Against Cod Liver Oil’s Ineffectiveness
| Supplement Type | EPA/DHA Dose | Heart Benefit (vs. placebo) | Key Study Source | Vitamin Content |
|---|---|---|---|---|
| Fish oil (EPA/DHA-only) | 1,000–2,000 mg/day | 19% lower major CV events | The Lancet (2026) | None |
| Cod liver oil | ~200–300 mg EPA/DHA | No significant effect | JAMA Network Open (2025) | High vitamin A/D |
| Prescription omega-3s* | 4,000 mg EPA/DHA/day | 25% lower CV death risk | NEJM (2024, REDUCE-IT trial) | None |
Prescription-strength omega-3s (e.g., Vascepa) are distinct from over-the-counter fish oil, with higher EPA doses and FDA approval for reducing heart attack risk in high-risk patients.
For more on this story, see This “Healthy” Food Could Worsen Fatty Liver, Experts Warn.
The confusion stems from historical marketing of cod liver oil as a “whole food” alternative to fish oil, despite its lower omega-3 content. A 2023 survey by the Consumer Health Research Institute found that 43% of respondents believed cod liver oil was as effective as fish oil for heart health—a misconception reinforced by older studies that lumped all omega-3 sources together.
Clinical Recommendations Differentiate Fish Oil for Heart Patients from Cod Liver Oil’s Limited Use Cases
- High triglycerides (≥150 mg/dL)
- History of heart attack or stroke
- Type 2 diabetes
For these groups, the American Heart Association (AHA) now recommends 1,000 mg EPA/DHA daily from supplements, in addition to statins or other medications. However, the AHA does not endorse cod liver oil for heart health due to its low omega-3 content and vitamin A risks.
- Pregnant women (excess vitamin A linked to birth defects)
- People with liver disease (vitamin A toxicity risk)
- Those taking blood thinners (cod liver oil’s vitamin K may interfere)
While fish oil supplements have earned a place in heart disease prevention, cod liver oil’s role remains limited to specific deficiencies, not cardiovascular protection.
- For heart health: Choose fish oil with ≥1,000 mg EPA/DHA (look for labels listing both amounts).
- For vitamin D/A: Cod liver oil may help—but monitor intake to avoid toxicity.
“Cod liver oil isn’t ‘bad,’ but it’s not a heart supplement,” said Dr. Chowdhury. “If you’re taking it for vitamins, great. If you’re taking it for your heart, you’re probably wasting your money—and missing out on the real benefit.”
Consult your healthcare provider before starting any omega-3 supplement, especially if you have liver disease, diabetes, or are on blood thinners.
