Fish oil supplements did not prevent atrial fibrillation in patients who had already experienced episodes of the heart rhythm malfunction, a new clinical trial has found.
The study, published in the Journal of the American College of Cardiology, adds to a growing pool of disappointing evidence regarding the protective effects of omega-3 fatty acids on heart health.
"The results for atrial fibrillation are important negative findings, answering key clinical and research questions," said Dr. Dariush Mozaffarian, an omega-3 expert at the Harvard School of Public Health, who was not involved in the current study.
The new research, combined with other trials, "indicates that short-term fish oil use is unlikely to prevent recurrent atrial fibrillation," he said.
But if the supplements don't prevent heart rhythm problems, they don't appear to be dangerous, either. "In all these studies, fish oil was safe and well-tolerated, with no evidence for increased bleeding," Mozaffarian told Reuters Health.
Atrial fibrillation, in which the heart's upper chambers beat out of step with those below, affects nearly one in 10 Americans in their 80s. The condition is linked to potentially life-threatening strokes and heart failure.
Although doctors prescribe certain medications to treat the condition, none to date has proven particularly effective. As a result, most drug treatment focuses on preventing strokes by administering blood thinners to dissolve clots caused by the fibrillation.
Some evidence suggests that omega-3 fatty acids, found in oily fish like sardines and tuna, might reduce the risk of atrial fibrillation, although exactly how they would produce their effect is not clear.
A study published earlier this year in Circulation, for example, found that people with the most omega-3s in their blood had a 30 percent lower chance of developing an irregular heart beat than those with the lowest concentrations of the substances.
That 30 percent difference would work out to eight fewer cases of atrial fibrillation per 100 people - which would be a meaningful benefit if it could be enjoyed by those with fibrillation or at risk for it, just by consuming more omega 3s.
But the latest study suggests that it probably can't. The trial included 586 men and women with a history of atrial fibrillation who were given a gram a day of fish oil or dummy capsules for a year. Participants also were allowed to take other drugs to control their heart rhythms, as prescribed by their doctors.
At the end of the study period, about 24 percent of the people who took fish oil, and 20 percent of those who did not, had experienced a recurrence of atrial fibrillation - a difference so small, statistically, it was likely due to chance.
The supplements also did not appear to reduce the risk of other cardiovascular ailments - including stroke, heart attack, heart failure - or death from any cause.
The findings on atrial fibrillation echo results from a study led by Mozaffarian published in November, of patients recovering from heart surgery.
Even so, Dr. Alejandro Macchia, a cardiologist at the GESICA Foundation in Buenos Aires, who led the current study and collaborated with Mozaffarian on the previous one, said fish oil may still prove beneficial for heart health, at least in some patients.
"I am not sure the story is over," Dr. Macchia told Reuters Health. "I think we have enough evidence to say that there is no role of (omega-3 fatty acids) for the prevention of atrial fibrillation" in patients with a history of the condition, he said. "However in the context of primary prevention - those people who had never had a previous episode of atrial fibrillation - there is a reasonable room for a well-designed and very large clinical trial."