Eating fish, seafood, seeds and nuts rich in omega-3 fatty acids regularly may help to lower the risk of dying from heart attacks, studies from 16 countries suggest.

A diet that includes fish and omega-3 is thought to be a heart-healthy eating pattern with benefits on measures such as blood pressure and heart rate. But studies on fish oil supplements haven't consistently shown the same benefits.

Our bodies use omega-3s for blood clotting, digestion, muscle activity and growth.

Now researchers have pooled studies that measured blood or tissue levels of omega-3 fatty acids in more than 45,000 people to take a more detailed look the relationships between the foods and heart health.

Fatty fish such as salmon, trout, tuna, sardines are the richest sources of omega-3 fatty acids, according to the U.S. Department of Agriculture's nutrient database.

A plant-based omega-3 fatty acid called alpha-linolenic acid is found in walnuts, flaxseed oil, and canola oil and some other seed and nuts and their oils.

Senior author Dr. Dariush Mozaffarian, dean of nutrition at Tufts University in Boston, and his team reviewed the studies on people in the U.S., Australia, Costa Rica, Finland, France, Germany, Ireland, Israel, Italy, Norway, Singapore, the former Soviet Union, Spain, Sweden, Switzerland, and the United Kingdom.

They found nearly 8,000 had a first heart attack over time, including 2,781 deaths.

Consuming omega-3s from plant and seafood sources several times a week was associated with about a 10 per cent lower risk of fatal heart attacks, the researchers said in Monday's issue of the journal JAMA Internal Medicine.

The researchers did not find a reduced risk of non-fatal heart attack with higher blood levels of seafood- and plant-based omega-3s.  

"At a time when some but not other trials of fish oil supplementation have shown benefits, there is uncertainty about cardiovascular effects of omega-3s,"  Mozaffarian said in a release.

"Consumption of omega-3 rich foods should be encouraged," the researchers wrote. 

The findings provide the most comprehensive picture of how omega-3s may influence heart disease, the researchers said.

Use of fish oil supplements was low in the studies that asked about it.

The study was funded by the U.S. National Institutes of Health and funders in Europe, Asia, and Australia. Some of the study's authors reported receiving grants, fees or honoraria from multinational food and pharmaceutical companies.