From Cod-Liver Spoons to Cardiology Labs: How Fish Oil Moved From Folklore to Precision Medicine

A spoonful that changed public health

In the early 1900s, cod liver oil wasn't "supplement culture." It was policy. As vitamin D emerged as the antidote to rickets, public health campaigns in Britain and beyond pushed cod liver oil into kitchens and clinics, all but erasing a disease that warped growing bones. The story is well-documented: cod liver oil, sunshine, and fortified milk turned a scourge into a memory. ^{[1] [2]}

Greenland, a dogsled, and a new hypothesis

In 1970, young Danish physicians Hans Olaf Bang and Jørn Dyerberg traveled by dogsled across Greenland to study Inuit seal hunters. Their blood looked different—rich in unusual fats later named EPA and DHA. "From that moment omega-3 was born," Dyerberg recalled decades later. ^[3] The idea that certain marine fats could protect the heart leapt from the ice into labs around the world. But early romance morphed into a more complicated reality.

What the biggest modern trials really show

Start with VITAL: 25,871 generally healthy U.S. adults took 1 gram/day of marine omega-3s or placebo. The headline was restraint: no significant reduction in the combined endpoint of heart attack, stroke, and cardiovascular death. Yet inside the data lived a plot twist—heart attacks dropped 28% overall, especially in people who ate little fish and among Black participants. As principal investigator JoAnn Manson put it, "there were several findings pointing to a coronary benefit." ^[4]

Now shift to patients with high triglycerides on statins. In REDUCE-IT, a purified EPA-only drug (icosapent ethyl, 4 g/day) cut major cardiovascular events dramatically; U.S. patients saw hazard ratios around 0.69 for key endpoints—numbers cardiologists rarely see outside statins and blood-pressure meds. ^[5] Contrast that with STRENGTH, which used a high-dose EPA+DHA oil: the trial was stopped for futility; events were unchanged, and atrial fibrillation was higher in the fish-oil arm. ^[6]

Zoom out to meta-analyses and a hard truth appears: across large outcomes trials, omega-3 supplements—especially at higher doses—are linked to a modest increase in atrial fibrillation risk. Said plainly: more oil isn't always better, and in some hearts it may nudge the rhythm off beat. ^[7]

The takeaway is nuance, not nihilism. Dose, formulation, and baseline diet matter. EPA-only therapy at prescription strength shows cardiovascular benefit in high-risk, high-triglyceride patients. Mixed EPA+DHA supplements in the general population? Benefits are smaller, most visible in people who rarely eat fish. ^{[4] [5] [6]}

When fish oil changes lives far from the cath lab

• Pregnancy: An updated Cochrane review pooling 70 randomized trials found that increasing long-chain omega-3s in pregnancy reduces preterm birth before 37 weeks by about 11% and early preterm birth before 34 weeks by 42%. The authors note many products don't match the studied dose—about 500–1000 mg/day with at least 500 mg DHA, typically starting around 12 weeks. ^[8]

• Rheumatoid arthritis: In a nine-month, double-blind trial, 39% of patients taking cod liver oil reduced NSAID needs by >30% (vs. 10% on placebo) without worsening disease scores. As study leader Jill Belch told the BBC: "I would advise people to give cod liver oil a try for 12 weeks alongside their NSAIDs." ^{[9] [10]}

• Triglycerides: Prescription omega-3s at 4 g/day reliably lower triglycerides ~20–30% and are indicated for very high levels; over-the-counter capsules aren't substitutes for that medical role. ^[11]

The hidden chapter: how the body "puts out the fire"

For years, scientists thought inflammation simply faded. Charles Serhan at Harvard helped flip that script by discovering specialized pro-resolving mediators—resolvins, protectins, maresins—built from EPA and DHA. These molecules don't block the first spark of inflammation; they coordinate the cleanup crew, telling immune cells when to stop fighting and start repairing. As Serhan says, "We want to stimulate the resolution pathways." ^[13] This lens explains why whole-diet patterns rich in marine fats may favor steady healing even when single-nutrient trials blur.

The quality question most people miss

Omega-3 oils are delicate. Heat, light, and time can turn them rancid—changing chemistry and taste. Independent testing of U.S. products (2014–2020) found a majority of flavored supplements exceeded voluntary oxidation limits; unflavored products fared better but still varied widely. Translation: choose brands with third-party testing (USP/NSF/IFOS), avoid excess heat, and be skeptical of candy-like flavors masking staleness. ^[12]

How to use fish oil wisely

If you rarely eat fish, a modest daily supplement can act like a dietary bridge, especially for heart-attack risk in the low-fish group seen in VITAL. Aim to get most omega-3s from food—two servings of oily fish weekly—and consider a supplement if that's unrealistic. ^{[4] [14]}

Practical pointers:

• Choose context before capsules. For very high triglycerides or high-risk patients, talk to a clinician about prescription options (e.g., EPA-only 4 g/day). ^{[11] [5]}
• During pregnancy, discuss omega-3s early; many trials used 500–1000 mg/day with at least 500 mg DHA starting around 12 weeks. Some programs stop by 34 weeks to avoid post-term pregnancy; ask your obstetric clinician what's right for you. ^[8]
• For joint symptoms, studies typically used 2–3 g/day EPA+DHA for at least 12 weeks; benefits tend to be NSAID-sparing rather than curative. ^[9]
• Take with meals containing fat for better absorption; store cool and dark. If a bottle smells sharply fishy, it may be oxidized. ^[12]
• Know your risks. High doses can increase atrial fibrillation risk; people with arrhythmia history should individualize decisions with their cardiologist. ^[7]

"There were several findings pointing to a coronary benefit," JoAnn Manson noted of VITAL's omega-3 arm—especially in people who ate little fish. ^[4]

"We want to stimulate the resolution pathways," Serhan says, hinting at a future where we harness the body's own stop-signals rather than just slamming the brakes. ^[13]

The larger lesson

Fish oil's journey—from rickets remedy to precision cardiology and pregnancy care—shows how science refines simple stories. The ocean still offers medicine. But it works best when we match the right fats, dose, and person—and remember that food, not just pills, is the most faithful messenger of the sea. ^[14]