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 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.

The new study was led by the Mario Negri Institute for Pharmacological Research in Milan. It tested one gram a day of fish oil vs. dummy capsules in 12,513 people throughout Italy. They had not suffered a heart attack but were at high risk.

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.