Eating fish is good for your heart, but taking fish oil capsules does not help people at high risk of heart problems who are already taking medicines to prevent them, a large study in Italy found.
The work makes clearer who does and does not benefit from taking supplements of omega-3 fatty acids, the good oils found in fish such as salmon, tuna and sardines.
Previous studies have suggested that fish oil capsules could lower heart risks in people with heart failure or who have already suffered a heart attack.
The American Heart Association recommends them only for people who have high levels of fats called triglycerides in their blood, says the group's president, Dr. Donna Arnett.
Fish oil capsules failed to prevent flare-ups of atrial fibrillation, a common heart rhythm problem, in a large study in 2010.
The new study was led by the Mario Negri Institute for Pharmacological Research in Milan. It tested 1 gram a day of fish oil versus dummy capsules in 12,513 people throughout Italy.
Most already were taking cholesterol-lowering statins, aspirin and other medicines to lower their chances of heart problems.
Researchers at first planned to compare the rate of death, heart attacks and strokes in the two groups, but these were less frequent than anticipated. So they started measuring how long it was before people in either group suffered one of these fates or was hospitalized for heart-related reasons. After five years, the rate was the same — about 12 percent of each group had one of these problems.
“When you're being aggressively treated for all of your other risk factors, adding fish oil yielded no additional benefits,” Arnett said.
Results are published in this week's New England Journal of Medicine.
The results show that people can't rely on a pill to make up for a bad diet, said Alice Lichtenstein of Tufts University.
“It is sort of like breaking a fish oil capsule over a hot fudge sundae and expecting the effect of the calories and saturated fat to go away,” she said.