Increasing intake of polyunsaturated fats, for example with omega-3 fatty acid supplements, has little or no effect in preventing the onset of depression or anxiety symptoms in people without these conditions, but who might be at risk. These findings support dietary advice that omega-3 supplements are not needed in healthy people.
This review also highlights that evidence of the effect of omega-3 in people with existing anxiety or depression is lacking or very limited. There remains not enough evidence to recommend that omega-3 fatty acids are bought by patients or as alternatives to currently recommended treatments for diagnosed depression and anxiety.
Very few of the included trials used foods or diet to increase polyunsaturated fat intake, and the review was focused on mental health outcomes. The review does not, therefore, address the potential importance of dietary polyunsaturated fats for general health.
Why was this study needed?
Over five million adults in England had diagnosed depression in 2018/19, which is around 10% of all adults registered with a GP. Generalised anxiety disorder affects around 5% of people in the UK.
There is some evidence linking depression or anxiety with low omega-3 or fish consumption, though poor mental health may lead to poor diet rather than the other way round. Omega-3 is a polyunsaturated fatty acid (PUFA) and has a long-chain form found in oily fish, and a short-chain form (alpha-linolenic acid) found in vegetable oils. Other PUFAs include omega-6, also found in vegetable oils.
Previous reviews have examined omega-3 for treating depression and anxiety, but the evidence was limited. No reviews of randomised trials have examined omega-6, total PUFA, alpha-linolenic acid, or their use for preventing depression or anxiety.
What did this study do?
This systematic review and meta-analysis compared the effects of higher and lower intake of omega-3, omega-6 and total PUFA on prevention and treatment of depression and anxiety in adults with or without these conditions. Interventions could be dietary advice, supplements or foods.
The review included 32 randomised controlled trials (RCTs) lasting at least six months, with 46,467 participating adults. All but two trials assessed long-chain omega-3, and most trials gave capsules or oils. The trials took place in Europe, North America, Australia and Asia, with four from the UK.
The quality of individual meta-analyses was graded, and clinically relevant effect sizes were pre-agreed with nutritional experts, to help interpret findings. Excluding lower quality or smaller trials from analyses did not substantially affect results, increasing confidence in the findings.
What did it find?
- Higher intake of long-chain omega-3 had little or no effect on the risk of depression symptoms (risk ratio [RR] 1.01, 95% confidence interval [CI] 0.92 to 1.10; 13 trials, 26,528 participants). About 5% developed depression symptoms in each group.
- Higher intake of long-chain omega-3 had little or no effect on the risk of anxiety symptoms in people without anxiety at baseline (SMD 0.15, 95% CI 0.05 to 0.26; result favours lower long-chain omega-3 intake; 5 trials, 1,378 participants).
- The effect of increasing intake of long-chain omega-3 on depression severity in people with depression at baseline, and on depression remission, is unclear because the evidence was of very low quality.
- No evidence was found to assess the effect of increased intake of any type of PUFA on anxiety severity in people with anxiety at baseline, or on anxiety remission.
What does current guidance say on this issue?
The NICE guidelines on generalised anxiety (2011, updated 2019) and social anxiety (2013) recommend explaining to patients the potential for over-the-counter preparations to interact with other medications, and the lack of evidence to support their safe use. The NICE guideline on depression (2009) does not discuss over-the-counter preparations generally.
The Royal College of Psychiatrists (2015) state there is not enough evidence to recommend omega-3 fatty acids as an alternative to antidepressants or mood stabilisers. The British Dietetic Association (2017) states that supplement use is currently not recommended in healthy adults and children.
What are the implications?
The review indicates that omega-3 does not prevent depression or anxiety in people without these conditions, reinforcing advice that healthy people do not need to take omega-3. The review found very limited or no evidence of the effect of omega-3 in people with existing depression or anxiety, supporting recommendations to explain to patients the lack of evidence for over-the-counter preparations. There remains not enough evidence to recommend omega-3 fatty acids as alternatives to antidepressants or mood stabilisers.
The review does not undermine the potential importance of foods rich in omega-3, such as oily fish, for a healthy diet for general health.
Citation and Funding
Deane KHO, Jimoh OF, Biswas P et al. Omega-3 and polyunsaturated fat for prevention of depression and anxiety symptoms: systematic review and meta-analysis of randomised trials. Br J Psychiatry. 2019; Oct 24. doi: 10.1192/bjp.2019.234. [Epub ahead of print].
This study was funded by the World Health Organization Nutrition Guidance Expert Advisory Group (NUGAG) Subgroup on Diet and Health (via the University of East Anglia) (grant number 2017/695622-0).
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NICE. Depression in adults: recognition and management. CG90. London: National Institute for Health and Care Excellence; 2009.
NICE. Generalised anxiety disorder and panic disorder in adults: management. CG113. London: National Institute for Health and Care Excellence; 2011 (updated 2019).
NICE. Social anxiety disorder: recognition, assessment and treatment. CG159. London: National Institute for Health and Care Excellence; 2013.
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