The meta-analysis study – published in JAMA Internal Medicine - included data from 45,637 participants in 19 trials throughout 16 countries.
People with the highest blood levels of omega-3 fatty acids had around a 25% lower risk of dying from a heart attack compares to those with the lowest levels. Overall, omega 3s from both plant and seafood sources were associated with a 10% lower risk of a fatal cardiac event.
However, higher levels of seafood and plant-based omega-3 fatty acids in the blood were generally not associated with non-fatal heart attacks. The team said this suggests a more specific mechanism for benefits of omega-3s related to death.
"These new results, including many studies which previously had not reported their findings, provide the most comprehensive picture to-date of how omega-3s may influence heart disease," said Dr Liana Del Gobbo, the cardiovascular research fellow at Stanford University School of Medicine who led the study.
Some trials have shown benefits of supplementation, though others have not, leading to uncertainty around the cardiovascular effects of omega-3s, Dr Dariush Mozaffarian, senior author on the study and a dean at Tufts University, Boston added.
"Our results lend support to the importance of fish and omega-3 consumption as part of a healthy diet," he said.
Victoria Taylor, senior dietician at the British Heart Foundation, agreed the study gives extra weight to recommendations over eating omega-3 rich oily fish like sardines, salmon and mackerel as part of a balanced diet and for heart health benefits.
“This study reinforces those recommendations and suggests there may also be a heart health benefit to omega-3 fats that come from vegetarian sources, such as flaxseed, rapeseed and soya oils, but more research would be needed to confirm these findings,” she said.
The analysis follows another recent meta-analysis, which suggested giving cardiac surgery patients omega-3 polyunsaturated fatty acids (PUFAs) beforehand had their hospital stays cut by as much as 2.4 days.
The researchers looked at biomarkers in participants’ blood of seafood-derived omega-3 fatty acids eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) in relation to coronary heart disease. Plant-derived omega-3 α-linolenic acid (ALA) was also a biomarker.
Specific blood measures were total plasma, phospholipids, cholesterol esters as well as adipose tissue.
The ALA biomarker was associated with a 9% lower risk of fatal heart attack, and DPA and DHA both had a 10% lower risk. DPA was also associated with a 6% lower risk of heart attack in general – not just fatal events – though ALA, EPA and DHA were not.
Dr Mozaffarian said measuring omega-3 levels in the blood is important since most previous study rely on participants reporting their intake, whereas the new study looks at impartial blood samples. Relying on participant diaries and self-reporting is not generally recognised as the most accurate form of data accumulation.
He said: "This new global consortium provides an unprecedented opportunity to understand how blood biomarkers of many different fats and fatty acids relate to diverse health outcomes, and many additional investigations are in progress."
However, despite the new research providing further evidence of omega-3 benefits, Taylor stressed there is still some way to go in educating consumers.
She said: “Although eating a portion of oily fish a week has been recommended as part of a healthy balanced diet for some time, we know that there is still a way to go before people are meeting these recommendations.
“At the moment we just eat around a third of a portion a week on average.”
'you need all omega-3s'
Harry Rice, PhD, vice-president of regulatory and scientific affairs at the Global Organisation for EPA and DHA Omega-3s (GOED) commented after publication.
"As confirmed by this research, you need all omega-3s in your diet. One does not substitute for the others. In fact, the strongest risk reductions you see in this paper are when
EPA/DHA reach the levels seen in the Japanese population. Keep in mind also that while we consume adequate ALA in our diet, the majority of populations don't get enough EPA and DHA."
A recent world map of omega-3 consumption globally showed most populations have levels too low for any cardiovascular benefits.
JAMA Internal Medicine
Published online June 27, 2016. doi:10.1001/jamainternmed.2016.2925
'ω-3 Polyunsaturated Fatty Acid Biomarkers and Coronary Heart Disease: Pooling Project of 19 Cohort Studies'
Authors: Del Gobbo LC, Imamura F, Aslibekyan S, et al.