The "accrual of high-level evidence" indicates "that the supplements lack efficacy across a range of health outcomes for which their use is advocated." That pronouncement, a conclusion that comes from an analysis of 24 studies based on randomized clinical trials and published in JAMA Internal Medicine in 2014, is hardly a ringing endorsement. But as the Washington Post reports, we buy those supplements anyway, and lots of them: Americans spend roughly $1.2 billion each year on fish oil pills and associated products; one of the authors of that JAMA research told Reuters in 2013 that about 10% of Americans take them. They're touted for the good fatty acids—omega-3s—they contain. But while they're generally considered safe to take, it's pretty unclear whether they're beneficial for heart health.
Writing for the Post, Peter Whoriskey astutely points out that even the National Institutes of Health and American Heart Association can't really make up their minds. The former endorses the supplements, then states "omega-3s in supplement form have not been shown to protect against heart disease" on its website; a scientific consultant with the NIH says the endorsement was supplied by a third-party contributor. As for the AHA, it advises people battling heart disease to ask their doctor about the supplements, but a former AHA president tells Whoriskey, "It would be a good time for that to be updated." As for those 24 aforementioned studies, all but two showed no benefit. But Whoriskey notes it's possible there is some, and our experiments on heart disease patients just can't pick up on it because heart medications cloud things. A 5-year study of 26,000 people—who the New York Times terms "more representative of the general population"—is due to be completed in 2016. (Another vitamin supplement could cause acne.)