The finding comes from European researchers including Ingeborg Brouwer, PhD, who works in the Netherlands at the Wageningen Centre for Food Sciences.
An ICD is an implanted electronic device that monitors the heart's rhythm. If the heart's electrical rhythm becomes abnormal, the ICD shocks the heart back to a normal rhythm.
Fish oil has been shown to have heart benefits in people without ICDs, but results have been mixed in people with ICDs, note Brouwer and colleagues.
Brouwer's team wanted to learn more about fish oil's heart effects on people with ICDs. So they studied 546 patients with ICDs for a year, on average.
The results, published in The Journal of the American Medical Association, show no heart benefits or risks from fish oil pills.
Fishing for Data
Between October 2001 and August 2004, Brouwer and colleagues recruited ICD patients from 26 cardiology clinics in eight European countries: Poland, Germany, the Netherlands, U.K., Czech Republic, Belgium, Austria, and Switzerland.
On average, participants were in their early 60s.
Brouwer's team randomly split them into two groups. They assigned one group to take 2 grams of fish oil per day in pills. That amount equals two to three portions of salmon or mackerel per week, the researchers note.
For comparison, they gave the other group placebo pills, which contained no fish oil.
Participants took the pills for a year, on average, not knowing if their pills contained fish oil. They also took a quarterly dietary survey to track their fish consumption and gave blood samples before and after the study.
Brouwer's team tested those blood samples for omega-3 fatty acids, fish oil's key type of fat. They also tracked patients' deaths from any cause and ICD heart shocks.
No Heart Benefits or Hazards Seen
Blood levels of omega-3 fatty acids rose in the fish oil group. But the study's most important measures -- survival and number of ICD heart shocks -- were similar in both groups.
In short, the patients taking fish oil didn't have any advantages or disadvantages in those areas.
During the study, 81 patients in the fish oil group died and/or got heart shocks from their ICDs, compared with 90 in the placebo group, the study shows.
That difference was so small that it might have been due to chance, according to the report.