Initial Posting: 4/4/2015    Last Update: 1/26/2020
Answer: Yes and no. It depends on the person and the fish oil.
Taking fish oil supplements has generally not been shown to prevent heart attacks or stroke in people who have heart disease, nor has it been shown to prevent heart disease in healthy people. (There is evidence, however, that fish oil supplements can be beneficial for other conditions, including inflammatory diseases, eye disease, and mental health disorders). However, among people who have high levels of triglycerides (which contributes to total cholesterol), high-dose, high-concentration fish oil, such as from prescription fish oils, may be beneficial, as they can lower triglyceride levels. However, only one prescription fish oil has been found to reduce the risk of first-time heart attack, stroke or other major cardiac event among statin-treated adults with persistently elevated triglycerides.
Keep in mind that having high blood levels of omega-3s and regularly consuming fish high in omega-3s (such as tuna and salmon, anchovies, and mackerel) is associated with a lower risk of cardiovascular disease. In one long-term study, for example, healthy older people who were not taking fish oil supplements but had higher blood levels of omega-3s were found to be 40% less likely to have a heart attack. The American Heart Association recommends consuming at least 1 to 2 fish servings of non-fried, preferably oily fish, per week to reduce the risk of cardiac death, coronary heart disease, and ischemic stroke (the most common type of stroke).