Omega-3 intake for cardiovascular disease

By: Abdelhamid AS, Brown TJ, Brainard JS, Biswas P, Thorpe GC, Moore HJ, Deane KHO, Summerbell CD, Worthington HV, Song F, Hooper L
Published: 29 February 2020

Review question

We reviewed randomised trials (where participants have an equal chance of being assigned to either treatment) examining effects of increasing fish- and plant-based omega-3 fats on heart and circulatory disease (called cardiovascular diseases, which include heart attacks and stroke), fatness and blood fats (lipids, including cholesterol, triglycerides, high-density lipoprotein (HDL – 'good' cholesterol) and low-density lipoprotein (LDL – 'bad' cholesterol)).

Background

The main types of omega-3 fats are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), both found in fish, and alpha-linolenic acid (ALA) found in plant foods. Many people believe that taking omega-3 supplements reduces risk of heart disease, stroke and death.

Trial characteristics

The evidence is current to February 2019. The review included 86 trials involving 162,796 people. These trials assessed effects of greater omega-3 intake versus lower omega-3 intake for at least a year on heart and circulatory disease. Twenty-eight trials were very trustworthy (well-designed so as not to give biased results). Participants were adults, some with existing illness and some healthy, living in North America, Europe, Australia and Asia. Most EPA and DHA trials provided capsules, few gave oily fish.

Key results

Increasing EPA and DHA has little or no effect on deaths and cardiovascular events (high-certainty evidence) and probably makes little or no difference to cardiovascular death, stroke, or heart irregularities (moderate-certainty evidence). However, increasing EPA and DHA may slightly reduce risk of coronary death and coronary events (low-certainty evidence, coronary events are illnesses of arteries supplying the heart). To prevent one person having a coronary event, 167 people would need to increase their EPA and DHA, and 334 people would need to increase their EPA and DHA to prevent one person dying from coronary disease. EPA and DHA reduce triglycerides by about 15% but do not affect fatness or other lipids (high-certainty evidence).

Eating more ALA (for example, by increasing walnuts or enriched margarine) probably makes little or no difference to all-cause, cardiovascular or coronary deaths or coronary events but probably slightly reduces cardiovascular events and heart irregularities (moderate- or low-certainty evidence). To prevent one person having a coronary event, 500 people would need to increase their ALA, 91 people to prevent one person having arrhythmia.

There is little evidence of effects of eating fish. EPA and DHA reduce triglycerides. EPA, DHA and ALA may be slightly protective of some heart and circulatory diseases.