Fish oil supplements rich in omega-3 fatty acids do not lower the risk of heart disease, a study has found.

These supplements were considered good for the heart and the brain. Surveys had shown that more than 30 percent of people living in the U.S. used these supplements for various health reasons. USA Today reported that Americans spent $1.1 billion in omega-3 supplements last year.

However, the researchers at the University Hospital of Ioannina, Greece, have found that the health benefits of these pills may not be as good as previously believed.

The researchers reviewed data available from large randomized trials to find any association between omega-3 polyunsaturated fatty acids (PUFAs) and heart disease risk. The review included 20 studies involving 68,680 patients.

The researchers found no statistically significant association between death due to heart attack or stroke and omega-3 supplementation. "Our findings do not justify the use of omega-3 as a structured intervention in everyday clinical practice or guidelines supporting dietary omega-3 PUFA administration," the authors wrote.

"Randomized evidence will continue to accumulate in the field, yet an individual patient data meta-analysis would be more appropriate to refine possible associations related to, among others, dose, adherence, baseline intake and cardiovascular disease risk group," the authors concluded.

Dariush Mozaffarian, MD, of Harvard's School of Public Health, who wasn't involved in the present study, told WebMD that the participants might have been taking other medication or lower doses of omega-3 supplements and so the study didn't find any association between the supplements and the heart attack risk.

"The good news is that the combined evidence from controlled trials confirms that fish oil reduces death from heart disease. The bad news is that effect appears smaller than we had thought -- about a 10% lowering of risk," Mozaffarian added.

The study was published in the Journal of the American Medical Association.