Most fish oil supplements make unsupported heart health claims, finds new study. Here's why experts say most people can skip them.

For years, fish oil supplements were promoted as an important way to boost health and particularly heart health. But recent research has shown mixed results on their impact, despite some supplement companies continuing to promote their products as having a big influence on health.

Still, nearly 10% of U.S. adults take fish oil supplements. Now, a new study finds that many fish oil companies make claims that are untested, and that a wide variety of amounts of omega-3 fatty acids — the core healthy fats in fish oil — are in their supplements.

What the study says

The study finds that the majority of fish oil supplements on the market make health claims that aren't backed up by clinical trial data.

What are the key findings?

For the study, researchers analyzed the labels of more than 2,800 fish oil supplements and found that 2,082 (or nearly 74%) made at least one health claim. Of those, only 399 (19.2%) used a qualified health claim that was approved by the Food and Drug Administration (FDA). (A qualified health claim means that the statements are supported by scientific evidence.)

But nearly 81% of those supplements made claims about the structure or function of what the supplements could do, such as saying that they "promote heart health," with cardiovascular claims being the most common.

The researchers also found "substantial variability" in the supplements' daily dose of omega-3s EPA and DHA — two major compounds in fish oil.

The researchers noted in the study's conclusion that most fish oil supplement labels make health claims "that imply a health benefit across a variety of organ systems, despite a lack of trial data showing efficacy." There is also "significant" diversity and quality in the daily dose of EPA and DHA in supplements, "leading to potential variability in safety and efficacy" between them.

Joanna Assadourian, lead study author and a fourth-year medical student at University of Texas Southwestern Medical Center, tells Yahoo Life that "based on what I’ve seen personally in the grocery store and pharmacy, I was not surprised to find such high rates of health claims on fish oil supplements. What was surprising, though, was just how broad the types of claims being made was — from heart and brain health to joint health, eye health and immune function."

The study's co-author, Dr. Ann Marie Navar, associate professor of medicine at University of Texas Southwestern Medical School, tells Yahoo Life that "as a preventive cardiologist, I see patients in clinic all the time taking fish oil with the belief it is helping their heart. They are often surprised when I tell them that randomized trials have shown no benefit for fish oil supplements on heart attacks or strokes."

Navar adds: "And we’ve all been in the supplement aisles of the grocery store or pharmacy and seen the massive number of products all claiming different types of potential health benefits. We wanted to better characterize what types of claims are being made on fish oil supplement labels."

What experts think

It's worth noting that supplements are a largely unregulated industry in the U.S. Companies can put new supplements on the market without FDA approval — they're just expected to adhere to FDA guidelines about safety and labeling. The agency also monitors reports of adverse events after products are up for sale.

"This is an important reminder that supplements are not FDA regulated, and you may not truly know what is in the bottle, despite what the label says," Dr. Ali Haider, an interventional cardiologist at NewYork-Presbyterian Queens, tells Yahoo Life. "This also highlights that the ‘health benefits’ touted by many supplement manufacturers are often not based on real evidence and are misleading. Patients need to be aware and educated before spending money on unhelpful products."

This is an issue with all supplements, Dr. Cheng-Han Chen, an interventional cardiologist and medical director of the Structural Heart Disease Program at MemorialCare Saddleback medical center in Laguna Hills, Calif., tells Yahoo Life. "I always tell patients to be cautious with supplements because any manufacturer can put anything they want in a pill and say whatever they want about it," he says. "Fish oil is no different."

Why do so many people continue to take fish oil supplements despite this? "Many people take fish oil because of longstanding beliefs about its potential health benefits, particularly for heart health," registered dietitian Scott Keatley, co-owner of Keatley Medical Nutrition Therapy, tells Yahoo Life. "The supplement industry, anecdotal evidence and earlier studies have often promoted these benefits. Once a narrative becomes deeply embedded in popular culture, it can be difficult to change, even when new evidence emerges."

When doctors use DHA and EPA in clinical practice, "it's generally at doses of 2 to 4 grams a day to help lower triglyceride levels in patient with high triglycerides," Haider says. (Triglycerides are levels of fat in the blood.) But, he adds, "studies have not shown that fish oil supplements reduce your risk of heart attack or stroke."

Navar admits that the messaging around fish oil supplements is "confusing," chalking it up to evolving science and slow administrative processes. "Epidemiologists first found that people who eat more fish and who have higher levels of EPA and DHA in their blood have less heart disease," she explains. "This led people to think there could be a benefit to fish oil. In fact, this type of data is what led the FDA in 2003 to approve a qualified health claim for fish oil that it may lower the risk of coronary heart disease."

But several large, high-quality, placebo-controlled randomized trials since then haven't shown any benefit for the general population to take fish oil to prevent heart disease. "Despite these two trials showing no benefit, many people still believe fish oil has some benefit," Navar says. "The landscape here is really confusing — even though large clinical trials show no benefit for prevention of heart disease, the 2003 FDA qualified health claim is still active." As a result, manufacturers of fish oil supplements can legally make claims like "promotes heart health," even though recent data doesn't support that, she says.

Why it matters

There are two FDA-approved fish oil-based drugs, "but they're for very specific indications, like people with high triglycerides," Chen says. For everyone else, fish oils aren't really recommended.

"There is potential harm in taking fish oil supplements," Chen says. "They may have additives and fillers, and we don't know what they are." Fish oil can also raise the risk of bleeding and atrial fibrillation, he says.

"I tell my patients that large, placebo-controlled trials have failed to show any benefit for prevention of heart attacks and strokes, so if they are taking it to try to lower their risk of those, they can stop," Navar says. "There are far more effective pills to lower the risk of heart attack and stroke — and fish oil supplements aren’t usually covered by insurance, so they can get expensive."

Chen recommends speaking to your doctor before taking a fish oil supplement. "Initially, we thought that fish oil was better for treating heart disease than it turned out to be," he says.

Assadourian agrees, saying: "Supplement labels can be confusing even for the most savvy of consumers. Patients should talk to their doctor about what supplements they are taking and why they are taking them — they may be surprised to learn that they are not getting the health benefits they think they are."