Are Fish or Fish Oil Supplements Good for the Heart?

Michael Greger M.D. FACLM · October 28, 2024 · Volume 67

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Five massive new trials have been published recently, randomizing tens of thousands to various formulations of fish oil versus placebo.

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Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Thanks in part to the American Heart Association’s recommendation that individuals at high risk for heart disease ask their physicians about omega-3 fish oil supplementation, fish oil pills have grown into a multibillion-dollar industry. We now consume more than a hundred thousand tons of fish oil every year. But what does the science say? Are the purported benefits of fish oil supplementation for the prevention and treatment of heart disease promising, or just a fish tale?

The scientific sea change occurred a little over a decade ago when a systematic review and meta-analysis published in the Journal of the American Medical Association looked at all the best randomized clinical trials evaluating the effects of omega-3 fats on life span, cardiac death, sudden death, heart attack, and stroke. These included studies not only on fish oil supplements, but also studies on the effects of advising people to eat more oily fish. Overall, the researchers found no protective benefit for overall mortality, heart disease mortality, sudden cardiac death, heart attack, or stroke. What about for someone who had already had a heart attack and is trying to prevent another? Still no benefit was found.

Since then, another five dozen randomized, controlled trials have been compiled, and the most extensive systematic assessment confirmed that increasing the intake of fish fats (EPA and DHA) has “little or no effect on deaths and cardiovascular events.” Longevity experiments on mice found no benefits for aging or lifespan either. Where did we even get this idea that the omega-3 fats in fish and fish oil supplements were good for us?

There was a notion that Eskimos were protected from heart disease, but that appears to be a complete myth. Some early studies, however, looked promising. For example, the famous DART trial from the 1980s involving two thousand men found that those advised to eat fatty fish had a 29 percent reduction in mortality. That’s impressive—no wonder the study got a lot of attention. Fish oil became a whale of a story that got bigger with every telling. But people seem to have forgotten about the sequel, the DART-2 trial, which found the exact opposite. Run by the same group of researchers, the DART-2 trial was an even bigger study—three thousand men—but this time, participants advised to eat oily fish, and particularly those who were supplied with fish oil capsules, had a higher risk of cardiac death. Concerns about the potential pro-arrhythmic (irregular rhythm inducing) effects of fish oil has led to reviews containing titles like “Can Fish Oil Kill You?”. But again, little or no change in overall mortality risk has been found when all the studies are put together.

Beyond just concerns about persistent pollutants, such as dioxins and PCBs in fish oil supplements—even in “distilled” fish oil supplements––oxidation by-products have been found throughout the commercial fish oil supplements industry. Surveys of popular omega-3 supplements in Asia, Europe, the Middle East, Australia, and North America found that 24-92 percent exceeded the voluntary safety standards set by the industry (there’s no legal limit, at least in the United States). The country of origin didn’t seem to matter, perhaps because most fish oil products sold globally are evidently sourced from the same region (off the West coast of South America). Surprisingly, the best-before date also wasn’t helpful (in this study where nine out of 10 supplements exceeded safety standards, they were all tested at least nine months before the best-before dates). The more expensive ones were more contaminated, but this is thought to be an artifact of higher cost relating to higher concentrations. And those obtained from algae were better than those from fish.

The United States has the highest sales of fish oil in the world, exceeding a billion dollars a year. When three top-selling fish oil supplements in the U.S. were tested, they all exceeded the recommended maximum levels of oxidation products, though expanded testing to four dozen U.S. supplements only found 52 percent exceeded the limits, though these two tests may give false positives due to added colors or flavors. A USDA study found that more than 70 percent contained less EPA and/or DHA than stated on their labels. But the greater concern is not what fish oil supplements are lacking, but rather what’s not listed on the label––like the contaminants, oxidation by-products, and saturated fat, which may explain why fish-based omega-3s raise LDL cholesterol levels compared to plant-based omega-3s.

The public health implications of consuming oxidized fish oil are unclear, however. Animal experiments suggest chronic exposure can cause inflammation, organ toxicity, and accelerated atherosclerosis, but no long-term human studies have been done. Ironically, one of the reasons there haven’t been more clinical studies are the ethical concerns knowingly exposing people to oxidized fats. Yet that experiment is being carried out en masse as we speak, in bathroom medicine cabinets around the world.

After putting all the studies together, the authors of the landmark AMA journal meta-analysis concluded that there was no longer justification for the use of omega-3s in everyday clinical practice. What should doctors do when their patients follow the American Heart Association’s advice and inquire about fish oil supplements? As the director of Lipids and Metabolism at Mount Sinai’s cardiovascular institute put it: “Given this and other negative meta-analyses, our job as doctors should be to stop highly marketed fish oil supplementation to all our patients… .”

The research momentum was already in full swing, though, and five massive new trials have been recently published randomizing tens of thousands to various formulations of fish oil versus placebo. Four out of five flopped. The so-called ASCEND trial, the OMEMI trial, the STRENGTH trial, and the VITAL trial all failed to reduce deaths or cardiovascular events, but one final nail in the coffin appeared to be loose. The REDUCE-IT trial didn’t significantly reduce overall mortality, but did reduce a composite of cardiovascular events by 25 percent. It used a prescription-only dose of EPA, equivalent to eating about 150 cans of tuna fish a day. The problem is the placebo they used.

Unlike other trials that used more neutral oils like corn oil, the drug company that funded REDUCE-IT to promote its own product chose mineral oil for the control group, a classic drug industry trick where you try to make your product look better by comparing it against something worse. And, indeed the mineral oil “placebo” increased LDL cholesterol, and caused more than a 30 percent increase in C-reactive protein. No wonder the fish oil looked good in comparison. It’s possible some fish oil formulation will eventually prove to be helpful, but for now, meta-analyses “unequivocally demonstrate that there is no cardiovascular benefit” to over-the-counter fish oil supplements.

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Doctor's Note

For more on fish oil, see:

For more on DHA and Pregnancy, check out the podcast.

Want to know my omega-3 recommendations? See my Optimum Nutrient Recommendations.

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