THURSDAY, May 18, 2006 (HealthDay News) -- Putting a confusing twist on the health value of fish oil, a new study suggests that eating lots of fish may actually boost the risk of atrial fibrillation, a potentially dangerous heart condition, in certain people.
However, the heavy fish eaters in the study still had a lower risk of sudden death from heart problems, and the study's lead author said the research shouldn't stop anybody from eating fish.
In recent years, many doctors have urged patients to eat oily fish -- such as mackerel, herring, albacore tuna and salmon -- or take fish oil supplements. Both contain omega-3 fatty acids, which have been linked to better recovery from heart disease and a lower risk in older people of atrial fibrillation, in which the heart's electrical system malfunctions, and the muscle fails to beat in an orderly fashion.
But it's not entirely clear that omega-3 fats are good for the general population without heart disease. And some research has suggested they may actually boost the risk of atrial fibrillation in certain people, such as those younger than 60.
In the new study, researchers analyzed data from nearly 17,700 U.S. male doctors who took part in the Physicians' Health Study. The men answered questions about their fish consumption in 1983 and were asked in 1998 if they had developed atrial fibrillation.
After adjusting the data to account for factors like existing heart disease, the researchers found that men who ate fish more than five times a week were 61 percent more likely to develop atrial fibrillation, compared to those who ate fish once a month. In total, about 7 percent of all the men in the study said they developed the condition, which is somewhat common among the elderly but rarer among younger people.
The findings were to be released Thursday at the Heart Rhythm Society's annual meeting, in Boston.
What could explain the seemingly contradictory finding?
It's possible that omega-3 fatty acids may actually promote the development of atrial fibrillation in younger people but prevent it in older people who have other medical conditions, said study author Dr. Anthony Aizer, an electrophysiologist at New York University Medical Center.
He added that atrial fibrillation isn't as great a risk in people who don't have conditions like congestive heart disease and high blood pressure. "Younger people are significantly less likely to have these additional medical conditions," he said. "As a result, the risk in younger people as a whole is likely to be significantly lower."
Aizer acknowledged that the study didn't rely on "gold standard" methods, such as double-blind, placebo-controlled research. So, it's possible that another unknown factor could explain the rise in atrial fibrillation cases seen in study participants, he said.
That possibility makes sense to Dr. Marie-Noelle Langan, chief of electrophysiology at Lenox Hill Hospital in New York City. She said it's possible that the male doctors who ate a lot of fish each week were health-minded athletes, who can be prone to atrial fibrillation.
"It's possible this is a group of very fit people who run like maniacs," Langan said. "It doesn't take that many patients to throw off the statistics."
Langan's hospital plans to launch its own study into fish oil and atrial fibrillation.
So should you take fish oil supplements or eat a lot of oily fish?
"There is no evidence that it's dangerous for your life," said Dr. Francesco Santoni, who's also an electrophysiologist at Lenox Hill Hospital. However, "it's unclear what effect it has in the general population on arrhythmias," or heart rhythm disturbances.
Aizer had similar views. "The message of this study is not to stop eating fish," he said. "Fish may have different effects on different people. Lifestyle and dietary habits need to be tailored on an individual basis to promote overall health."
For now, he said, "clearly, more investigation is needed to reach a more definitive answer about the multiple effects of omega-3 fatty acid on the heart's electrical function."
Here's what the American Heart Association has to say about omega 3 fatty acids.