Many people take fish oil supplements thinking they are good for heart health. But can they help? A new study says although most labels that sell the supplements claim heart health benefits, they lack scientific evidence to prove the efficacy.

Researchers from the University of Texas Southwestern Medical Center examined more than 2,800 fish oil supplements sold in the market. They found that the levels of two crucial components of fish oil supplements – eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) – vary between products.

The study evaluated two types of claims made in connection with heart health: Qualified health claims and structure/function claims.

Qualified health claims are benefits in connection with the treatment or prevention of the disease. They are made by the U.S. Food and Drug Administration (FDA) after an evidence review. The structure/function claims, as the name suggests, are intended for the structural or functional benefit of an organ and do not have any role in the prevention, treatment or cure of any disease.

The research team found that 73.9 % of the supplement labels made at least one health claim – most of them (80.8%) made structure/function claims, while 19.2% used an FDA-qualified claim.

Researchers said there is only limited evidence to prove the efficacy of fish oil supplements. One in five people over age 60 take fish oil supplements for heart health.

"Multiple randomized clinical trials have shown no cardiovascular benefit to fish oil supplements," researchers observed.

"We know from recent large, randomized trials that fish oil supplements do not prevent heart disease in the general population, but yet they are one of the most common supplements taken, often by people who still believe they will benefit their heart," lead author Joanna Assadourian said.

To assert structure/function claim, fish oil supplements often use labels like "promotes heart health," and "supports heart, mind, and mood," which can create confusion and give misleading information to consumers.

"As a preventive cardiologist, I tell my patients that if they are taking fish oil to try to avoid heart disease then they can stop taking it because it's not helping them," co-author Dr. Ann Marie Navar said. Navar instead suggests including fresh vegetables in the diet, regular exercise and medication to treat blood pressure and cholesterol.

Researchers also observed that consumers should consult with a doctor to understand the benefits rather than blindly following the labels of supplements.

"Significant heterogeneity exists in the daily dose of EPA+DHA in available supplements, leading to potential variability in safety and efficacy between supplements. Increasing regulation of dietary supplement labeling may be needed to prevent consumer misinformation," the team said.