The theory that the supplements cause prostate cancer—first suggested in a paper published in 2013—has been debunked by researchers at the Intermountain Healthcare Heart Institute.
They tested 87 prostate cancer patients for levels of DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid), two common omega-3 fatty acids, and compared them with 149 healthy men, but couldn't find any link between omega-3 and the cancer.
In a second study, the researchers wanted to establish if the supplements could improve heart health—as they've been championed for doing. They tracked 894 patients who had no history of heart disease or any symptoms of heart problems, but when they had a coronary angiography—which shows how blood flows through the arteries to the heart—around 40 percent had severe heart disease and 10 percent had three-vessel disease, where three of the coronary arteries had become blocked.
Their levels of DHA and EPA were also measured, and those with the highest levels had the lowest risk of heart attack, stroke or heart failure later on.
Although those with high levels also might have some heart disease, they were invariably the survivors, the researchers added, suggesting that the omega-3s don't always have a preventative effect, but they do have a protective one.