The study found problems.
LOS ANGELES TIMES
First, fish oil was credited with reducing the risk of sudden death after heart attacks. Then it was linked to decreases in depression, possible improvements in children's brain development, and even possible protection against Alzheimer's disease and cervical cancer.
It has looked so promising, in fact, that researchers have pursued a seemingly endless array of fish oil's positive health associations.
Such optimism may have been premature.
A study in the June 15 issue of Journal of the American Medical Association found that for certain high-risk cardiac patients, fish oil supplements may do more harm than good.
People with a history of arrhythmias, or abnormal heart rhythms, and implanted cardiac defibrillators who took daily fish oil supplements were more likely to experience episodes of those rhythms than similar patients receiving only a placebo, the researchers found.
"We got a result we didn't expect," said Dr. Merritt H. Raitt, the study's lead author.
The study highlights how little actually is known about the supplements' effects -- and that even a nutrient with dozens of potential health benefits might have a few risks, as well.
"We also always have to be a little cautious when we start giving very high levels of individual nutrients," said Alice Lichtenstein, a professor of nutrition at Tufts University in Boston.
In the study, 200 patients at six medical centers -- all of whom had received an implanted defibrillator -- were given either 1.8 grams of fish oil or a placebo pill containing olive oil every day for up to two years.
Those receiving the fish oil were more likely to suffer an episode of arrhythmia than those receiving the placebo, with 46 percent of the fish oil group having an episode after six months, as compared to 36 percent of the placebo group. Arrhythmias are unusually fast or irregular heartbeats that can lead to serious injury or death.
Raitt said that the difference between this study and previous research, which has shown positive cardiovascular effects for fish oil, might be due to the specific characteristics of the study participants.
The study is "a reminder that pretty much all medication that can affect heart rhythm is a doubled-edged sword," Raitt said.
He and other medical experts cautioned that the study doesn't mean fish and fish oil supplements are not healthy.
"I would want to make sure people don't get the impression that they should stop eating fish," Raitt said.
The health benefits of including fish are well established, Raitt said, and people shouldn't shy away from including more fish in their diet.
Even fish oil supplements are still beneficial for most patients, Raitt said, especially those who have recently had a heart attack.
To get the omega-3 fatty acids that are so beneficial, the American Heart Association recommends at least two servings of fish per week, especially from fatty fish such as salmon or mackerel.