In the study, carried out in 2010 in Italy with 12,513 patients, half the group took an omega-3 supplement and the other half an olive oil placebo.
Previous clinical trials have suggested that these supplements could reduce cardiovascular risks for patients suffering from cardiovascular disease or who have already suffered cardiac arrest.
But a major study in 2010 found that the fish oil supplements did not help prevent atrial fibrillation, a common problem with the heartbeat's rate or rhythm.
The latest research found that just under 12 percent of patients in both groups -- 11.7 percent of the omega-3 group and 11.9 percent of the placebo group -- experienced a stroke.
"In a large general-practice cohort of patients with multiple cardiovascular risk factors, daily treatment with n-3 fatty acids did not reduce cardiovascular mortality and morbidity," the study concluded.
The research was led by Mario Negri at the Societa Prodotti Antibiotici in Milan.