Navigating the murky waters of supplements is no easy task, even with about half of all Americans taking some form of vitamins or minerals in pill form.
Fish-oil pills, which deliver omega-3 fatty acids that can have a blood-thinning effect, made about $1 billion in sales in 2012. A "Frontline" investigation released Tuesday looked into what actually goes into fish oils and whether those fish oils are actually doing what we think they do.
The short answer: It might be better to get your omega-3 fatty acids directly from fish than from a pill.
But the data it takes to arrive at this answer can get complicated. For one thing, it's hard to know what you're getting from the pills in terms of quality.
By the standards of the global fish-oil trade association GOED, about 20% of the 47 versions of fish-oil pills from New Zealand aren't up to industry standards for how intact the lipids, or fats, in the pills are, a spokesman for the organization told "Frontline." Fish oil is fairly sensitive, which means it can break down pretty easily into a form that's not helpful. But other studies have arrived at different conclusions — a different New Zealand-based study of the same types of pills found that roughly 83% were not of OK quality.
Despite these quality issues, there's also evidence that the supplements themselves — even those that are of a high quality — won't necessarily do the things they say they will.
For example, a 2002 study conducted by the American Heart Association said fish oil would help with reducing the risk of heart disease, and a clinical trial published through the Alzheimer's Association reported the supplements would improve brain health.
But other studies show otherwise. A 2012 study found that the evidence of omega-3 having an impact on the incidence of dementia is lacking. The supplement has been explored in trials to help such diseases as cancer and immune-system conditions. It's widely thought to help heart health, but an analysis of major fish-oil studies concluded that that's not the case. Only two of the 18 studies they looked at actually showed any benefit to taking the fish-oil supplement.
"For cardiovascular disease, one has to say there is no compelling evidence that taking fish oils protects against the first heart attack or a second heart attack," Dr. Andrew Grey, one of the authors of the study, told "Frontline."
But looking at much of the same evidence, the fish-oil trade association didn't come to the same conclusion.
"I think what you're looking at are the abstracts," Adam Ismail, GOED spokesman, told "Frontline." "Those papers are looking at large areas of cardiovascular disease. I think it's hard to argue that omega-3s aren't important for how your heart functions."
Watch a clip of the "Frontline"/PBS documentary:
More from Business Insider: