Millions of Americans — including one in five people over age 60 — take fish oil supplements, often assuming the capsules help stave off heart disease. Who can blame them? After all, the product labels say things like "promotes heart health" and "supports healthy cholesterol and blood pressure levels."
"People will often say 'I don't like eating fish, but I know it's good for me. So I'm taking this supplement instead,'" says Preston Mason, a faculty member in the Cardiovascular Division at Harvard-affiliated Brigham and Women's Hospital who studies the unique fats found in fish oil, known as omega-3 fatty acids.
Here's the catch: Studies dating back more than a half-century find that people who eat fatty fish tend to have lower rates of heart disease. But over the past two decades, multiple randomized trials pitting fish oil against placebos show no evidence of heart-related benefits from fish oil supplements. While the supplements do provide omega-3 fatty acids, there are better ways to get these essential fats from your diet (see "Three key omega-3s").
Three key omega-3s
Omega-3 fatty acids are considered "essential," which means people must get them from their diet or other sources. Fatty fish such as salmon, tuna, sardines, and mackerel are good sources of two omega-3s: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).
Another omega-3, alpha-linolenic acid (ALA), is found in many plants, including seeds, nuts, and some green vegetables. Your body can convert a small amount — about 8% — of dietary ALA to EPA and DHA.
Nutrition experts suspect that one reason fish eaters have fewer heart attacks may be that they eat correspondingly less red meat or processed meats, both of which are associated with a higher risk of heart disease.
Vegetarians (who don't eat fish) and vegans (who avoid all animal-based foods) can meet their omega-3 requirements by eating plenty of ALA-rich foods, such as flaxseed, walnuts, pumpkin seeds, and soybean or canola oil. People who follow these plant-focused diets have lower rates of heart disease than omnivores, who include animal-sourced foods in their diets.
Confusing health claims
What's up with the misleading messaging? The FDA considers all dietary supplements, including fish oil, to be foods, not drugs. Unlike companies that make aspirin, antacids, and other over-the-counter drugs, supplement manufacturers aren't required to do any rigorous clinical testing or undergo any production oversight, Mason explains. Despite this, they're allowed to include limited health claims on their labels, and heart-related promises are common on fish oil supplements, according to a study published October 1, 2023, in JAMA Cardiology.
Among the more than 2,800 different fish oil supplement labels the researchers checked, about 2,000 featured one or more heart-related statements. Most of these health claims (about 80%) featured general but vague descriptions of the role of omega-3 fatty acids in the body. Most (62%) were cardiovascular claims, such as "helps support a healthy heart."
In addition, the researchers analyzed 255 fish oil products from 16 major manufacturers and found a wide variability in the actual amounts of EPA and DHA (the two main omega-3 fatty acids) in the supplements. These findings confirm Mason's research.
What's more, many widely used fish oil supplements are produced through an industrial process that leaves the omega-3 fatty acids vulnerable to uncontrolled heat and oxygen, says Mason. "This results in the oxidation of these highly unsaturated fatty acids, with a consequent loss of any biological benefit," he says, adding that multiple laboratory tests on dozens of products have confirmed these findings. Consuming oxidized oil has been linked to vascular inflammation, a key cause of cardiovascular disease.
If you have heart disease, you might ask your doctor about the prescription drug icosapent ethyl, a high-dose, purified EPA preparation that lowers cardiovascular risk when taken with a statin. "The unregulated fish oil supplements found in stores and online are not an effective substitute," Mason cautions. If you don't have heart disease, eating two servings of fatty fish weekly or following a vegetarian diet rich in healthy oils, nuts, and seeds is a far smarter strategy than buying fish oil supplements.
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