Millions of Americans take fish oil supplements, hoping to keep their hearts at their healthiest. But a new study has raised questions about these popular dietary supplements, especially whether they can replace a healthy, balanced diet.

Fish oil, a combination of omega-3 fatty acids, is a centuries-old staple of pharmacy shelves, and scientists have devoted much research to investigating its effects on heart health. So far, the evidence has been inconclusive -- some studies have found fish oil has been major in preventing heart attacks, strokes and sudden cardiac death, while others have found fish oil has no benefits at all.

In the current study, published in the Archives of Internal Medicine researchers from South Korea analyzed 14 clinical trials involving more than 20,000 patients with cardiovascular disease who had taken fish oil supplements for at least one year and found the supplements did not reduce their risk of having another heart attack, stroke, congestive heart failure or any other cardiovascular catastrophe.

Fishy or not, fish oil is one of the most popular dietary supplements sold in the U.S. According to the Nutrition Business Journal, over-the-counter fish oil supplements reeled in $739 million in 2009 alone, according to a report in Forbes magazine. Foods fortified with extra omega-3s, such as margarine and peanut butter, roped in nearly $4 billion for manufacturers in 2010, according to Packaged Facts.

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