At issue are prescription-strength omega-3 fatty acids, which are naturally found in fish oil. The medications are often prescribed to people with very high triglycerides, a type of blood fat linked to increased risk of heart attack and stroke.
According to the American Heart Association, prescription omega-3s can lower triglycerides by 20% to 30% in most people.
But the medications are also controversial, because their ultimate benefits for the heart are unclear.
Now the new study — an analysis of five past clinical trials — suggests caution is in order. Overall, trial patients given omega-3s were over one-third more likely to develop atrial fibrillation (a-fib) than those given a placebo. The fish oil doses taken ranged from 0.84 grams to 4 grams per day.
A-fib is a common heart rhythm disorder, or arrhythmia, in which the heart’s upper chambers begin to quiver chaotically instead of contracting effectively.
A-fib is not immediately life-threatening, but it’s “not benign,” either, said Dave Dixon, one of the researchers on the study and an associate professor at Virginia Commonwealth University (VCU), in Richmond.
Over time, Dixon said, a-fib can lead to complications like heart failure or stroke.
Exactly how prescription-strength omega-3 could contribute to a-fib is unclear, according to Dixon.
However, the increased risk was fairly consistent across the trials — more consistent, in fact, than heart benefits were, said co-researcher Salvatore Carbone, an assistant professor at VCU.
In all five trials, there were more a-fib cases among omega-3 patients than placebo patients, though the difference in risk was not statistically significant in all studies.
But when the researchers pooled the results of all five trials, there was a clear result: Omega-3 patients were 37% more likely to develop a-fib than placebo patients were.
In contrast, only one trial showed that an omega-3 product could cut the risks of other heart conditions.
In that trial, dubbed REDUCE-IT, patients using a product called Vascepa (icosapent ethyl) saw their risk of “cardiovascular events” drop by 25%. That included heart attack, stroke and death from cardiovascular causes.