Fish oil -- a supplement taken daily by millions of Americans -- may not help you live longer, a new study released today suggests.
The study is the latest piece of research feeding the debate over whether regularly taking omega-3 supplements -- most commonly in the form of fish oil -- helps the heart.
A number of clinical trials have found that fish oil seems to lower risk of heart attack, sudden death, and even stroke -- though exactly how this works remains unclear. Yet, other studies have found little evidence of connection between these often pricey supplements and health benefits.
In the new report, published in the Journal of the American Medical Association, lead study author Dr. Evangelos Rizos and his colleagues completed an extensive review of existing data. They pooled results from 20 studies that included almost 70,000 adult patients.
Through rigorous statistical analyses, they said, they found no significant risk reduction in those getting increased omega-3 in their diet or through supplements.
Fish oil supplements are among the most popular dietary supplements among Americans. Though it is hard to pin down an exact figure for sales of such products, an article in Forbes magazine noted that, according to the Nutrition Business Journal, over-the-counter fish oil supplements accounted for $739 million in sales in 2009. Meanwhile, in 2010 Americans spent nearly $4 billion on products fortified with extra omega-3s, according to the market research firm Packaged Facts.
While the news may be disappointing to many expecting to live longer and have healthier hearts by taking these supplements daily, it's not the first time such findings have been reported. In April, a South Korean study of 20,000 people found a similar lack of heart benefits, and in June a separate study suggested that brain benefits, too, may have been oversold.
The results have some top cardiologists convinced that consumers should pause before buying these supplements.
"There's never been any compelling evidence of a clinical benefit," said Dr. Steven Nissen, professor of medicine at the Cleveland Clinic Lerner School of Medicine.
Despite these mixed results, however, many physicians still recommend these supplements, which can cost $40 or more per bottle.
"Patients and doctors like the idea that it is natural and has no real side effects," said Dr. Howard Weintraub, clinical director of New York University Center for the Prevention of Cardiovascular Disease.
And some doctors say the findings of the new study are no reason to cut bait on fish oil.
"Meta-analysis, particularly when neutral, should not be used to draw a conclusion," said Melvyn Rubenfire of the University of Michigan.
Rubenfire said many of the studies included in this report did not have long enough follow-up, noting that heart and stroke prevention studies "are generally designed with five-year duration." Many patients studied here, he said, were followed for less than three years.
Rubenfire added that he believes this information "should dampen the enthusiasm for routine costly supplement in healthy persons" -- but that he and many experts agreed that omega-3 supplements are still a good strategy for patient with high triglycerides.
Some experts also note that the report is limited because the authors only included results from 20 of the thousands of studies on this topic, as many of these studies vary in terms of the types of patients and the doses of fish oil studied.
"This inherently makes it hard to group them together for one analysis," said Dr. Merle Myerson, director of cardiovascular disease prevention at Continuum Health Partners.
Myerson said she thinks that while government guideline committees will consider this study, they won't "change or challenge current recommendations."
ABC News' Carrie Gann contributed to this report.