NIHR Signal Omega-3 supplements do not prevent heart disease, stroke or death
Published on 6 November 2018
Omega-3 fatty acid supplements from fish oils or plants have little or no effect on the risk of heart disease, stroke or overall death rates. This finding contradicts a widespread belief that omega-3 supplements are protective. Previous evidence in favour of omega-3 supplements is mainly derived from trials at high risk of bias. The better evidence identified in this review does not demonstrate any health benefit.
The review provides robust evidence confirming current guidance that omega-3 supplements should not be used to prevent cardiovascular disease. However, few of the trials included in this review looked at foodsources of omega-3. Other studies have demonstrated that intake of omega-3 is essential to human health, and it is possible that the intake of foods rich in omega-3 may have a place in a healthy balanced diet.
- Cardiovascular system disorders, Obesity and nutrition, Primary care
Why was this study needed?
Heart disease, stroke and arterial disease, all affect blood vessels. They account for one-third of deaths and, in 2010, cost NHS England £8 billion.
There is a widespread belief that omega-3 can protect against heart disease and stroke, and capsules containing purified omega-3 are widely used. Three different types of omega-3 are metabolically important for humans. These are eicosapentaenoic acid and docosahexaenoic acid, commonly found in marine algae, krill and fish; and alpha-linolenic acid found in seeds, nuts and legumes.
This review aimed to combine all trials of omega-3 supplementation to assess outcomes for all-cause mortality, cardiovascular events (except peripheral artery disease), lipid markers, and weight.
What did this study do?
This updated Cochrane review found 79 randomised controlled trials that compared increased omega-3 intake to usual or lower intake for at least 12 months. Most of the trials used supplements, but some used foods rich in omega-3 or offered dietary advice. Overall, 112,059 adults were included; participants included adults at low and high risk or with established cardiovascular disease. The trials took place in North America, Europe, Australia and Asia, with eight from the UK.
Twenty-five of the trials had a low risk of bias and can be considered highly trustworthy. The rest had a moderate or high risk of bias. Most of the studies assessed omega-3 supplementation with capsules but few examined the effects of other dietary sources, and so it is possible the health effects available from food sources differ.
What did it find?
- Increasing omega-3 intake showed no effect on overall risk of death (risk ratio [RR] 0.98, 95% confidence interval [CI] 0.90 to 1.03; 39 trials with 92,653 participants, high quality evidence). All-cause mortality was about 9% in both groups.
- Increasing omega-3 showed no effect on death from heart disease or stroke (RR 0.95, 95% CI 0.87 to 1.03; 25 trials with 67,772 participants, moderate quality evidence). Mortality from these causes was about 7% in both groups.
- Increasing omega-3 showed no effect on heart disease or stroke (RR 0.99, 95% CI 0.94 to 1.04; 38 trials with 90,378 participants, high-quality evidence). The risk of an event was about 16% in both groups.
- There is weak evidence that omega-3 may slightly affect serum lipid markers. No effect on body weight was found.
What does current guidance say on this issue?
NICE 2016 guidance on cardiovascular disease risk assessment and reduction states that there is no evidence that omega-3 fatty acid compounds help prevent cardiovascular disease.
It says that omega-3 should not be offered for primary or secondary prevention. It does, however, say that people at high risk of or with existing cardiovascular disease should eat at least two portions of fish each week, including a portion of oily fish, and 4-5 portions of nuts, seeds and legumes.
What are the implications?
This extensive systematic review provides evidence to support current NICE guidance that omega-3 supplements do not prevent heart disease or stroke. Previous claims for benefits of omega-3 supplements appear to come from trials with a higher risk of bias.
The findings do not mean that people should stop eating foods (such as oily fish, seeds, nuts, and legumes) that are rich in omega-3. These foods form an important part of a healthy diet.
Citation and Funding
Abdelhamid AS, Brown TJ, Brainard JS, et al. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev. 2018;7:CD003177.
Cochrane UK and the Cochrane Heart Group are supported by NIHR infrastructure funding.
Alhassan A, Young J, Lean MEJ et al. Consumption of fish and vascular risk factors: A systematic review and meta-analysis of intervention studies. Atherosclerosis. 2017;266:87-94.
NICE. Cardiovascular disease: risk assessment and reduction, including lipid modification. CG181. London: National Institute for Health and Care Excellence; 2016.
Fatty fish contain high amounts of long chain omega-3 fatty acids that have well-established effects in protecting against often fatal coronary events such as thrombosis and cardiac arrhythmia. How then can we explain this recent meta-analysis that found they had no effects on cardiac events, mortality or other measures of cardiovascular health?
These conclusions were based almost entirely on data from high dose purified capsule supplements of long chain omega-3 fatty acids and not oily fish. Also, we know that the benefits of these fatty acids are mostly seen in people with cardio-metabolic risk factors that were not specifically included in this meta-analysis.
Patients who could be seen to benefit from the protective effects of long chain omega-3 fatty acids were outnumbered by patients who showed no effects, producing an overall negative outcome.
Bruce A. Griffin, Professor of Nutritional Metabolism, University of Surrey