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Risks and benefits of omega 3 fats for mortality, cardiovascular disease, and cancer: systematic review

BMJ 2006; 332 doi: http://dx.doi.org/10.1136/bmj.38755.366331.2F (Published 30 March 2006)
Cite this as: BMJ 2006;332:752
  1. Lee Hooper, lecturer (l.hooper{at}uea.ac.uk)1,
  2. Rachel L Thompson, senior research fellow2,
  3. Roger A Harrison, senior research fellow3,
  4. Carolyn D Summerbell, professor4,
  5. Andy R Ness, senior lecturer5,
  6. Helen J Moore, research fellow4,
  7. Helen V Worthington, professor7,
  8. Paul N Durrington, professor8,
  9. Julian P T Higgins, statistician9,
  10. Nigel E Capps, consultant chemical pathologist10,
  11. Rudolph A Riemersma, professor11,
  12. Shah B J Ebrahim, professor12,
  13. George Davey Smith, professor6
  1. 1 School of Medicine, Health Policy and Practice, University of East Anglia, Norwich NR4 7TJ
  2. 2 Institute of Human Nutrition, University of Southampton, Southampton SO16 6YD
  3. 3 Bolton Primary Care Trust, Bolton BL1 1PP
  4. 4 School of Health and Social Care, University of Teesside, Middlesbrough TS1 3BA
  5. 5 Department of Community-based Medicine, University of Bristol, Bristol BS8 1TQ
  6. 6 Department of Social Medicine, University of Bristol, Bristol BS8 2PR
  7. 7 School of Dentistry, University of Manchester, Manchester M15 6FH
  8. 8 Department of Medicine, University of Manchester
  9. 9 MRC Biostatistics Unit, Cambridge CB2 2SR
  10. 10 Department of Clinical Biochemistry, Princess Royal Hospital, Shrewsbury and Telford Hospital NHS Trust, Telford TF1 6TF
  11. 11 Centre for Cardiovascular Science, University of Edinburgh, Edinburgh EH16 4TJ
  12. 12 London School of Hygiene and Tropical Medicine, London WC1E 7HT Department of Epidemiology and Population Health
  1. Correspondence to: L Hooper
  • Accepted 11 February 2006

Abstract

Objective To review systematically the evidence for an effect of long chain and shorter chain omega 3 fatty acids on total mortality, cardiovascular events, and cancer.

Data sources Electronic databases searched to February 2002; authors contacted and bibliographies of randomised controlled trials (RCTs) checked to locate studies.

Review methods Review of RCTs of omega 3 intake for 3 6 months in adults (with or without risk factors for cardiovascular disease) with data on a relevant outcome. Cohort studies that estimated omega 3 intake and related this to clinical outcome during at least 6 months were also included. Application of inclusion criteria, data extraction, and quality assessments were performed independently in duplicate.

Results Of 15 159 titles and abstracts assessed, 48 RCTs (36 913 participants) and 41 cohort studies were analysed. The trial results were inconsistent. The pooled estimate showed no strong evidence of reduced risk of total mortality (relative risk 0.87, 95% confidence interval 0.73 to 1.03) or combined cardiovascular events (0.95, 0.82 to 1.12) in participants taking additional omega 3 fats. The few studies at low risk of bias were more consistent, but they showed no effect of omega 3 on total mortality (0.98, 0.70 to 1.36) or cardiovascular events (1.09, 0.87 to 1.37). When data from the subgroup of studies of long chain omega 3 fats were analysed separately, total mortality (0.86, 0.70 to 1.04; 138 events) and cardiovascular events (0.93, 0.79 to 1.11) were not clearly reduced. Neither RCTs nor cohort studies suggested increased risk of cancer with a higher intake of omega 3 (trials: 1.07, 0.88 to 1.30; cohort studies: 1.02, 0.87 to 1.19), but clinically important harm could not be excluded.

Conclusion Long chain and shorter chain omega 3 fats do not have a clear effect on total mortality, combined cardiovascular events, or cancer.

Footnotes

  • Embedded ImageA complete set of references is available on bmj.com

    Thanks to Theresa Moore and Margaret Burke from the Cochrane Heart Group, and to all of the authors of primary studies who helped us build up the data. This paper is based on a Cochrane review accepted for publication in The Cochrane Library (see www.theCochranelibrary.net/ for information).

  • Contributors All authors commented critically on the manuscript and agreed the final version. NEC helped design the review, provided a clinical perspective, and commented on the analysis and interpretation. GDS helped design the review, provided a methodological perspective and general advice, and commented on the analysis and interpretation. PND provided a methodological perspective and expertise on omega 3 biochemistry, and commented on the analysis and interpretation. SBJE helped design the review, provided a methodological perspective and general advice, and commented on the analysis and interpretation. RAH screened retrieved papers against inclusion criteria, appraised quality of papers, abstracted data from papers, provided general advice, and commented on the analysis and interpretation. JPTH helped design the review, provided a statistical perspective and general advice, and commented on the analysis and interpretation. LH conceived the review, designed and coordinated the review, developed the search strategy and undertook searches, screened the search results, organised retrieval of papers, screened retrieved papers against inclusion criteria, appraised study quality, abstracted data from included papers, wrote to authors and experts for additional information, managed the review data, entered data into RevMan, analysed and interpreted the data, and was the primary author. HJM screened retrieved papers against inclusion criteria, appraised quality of papers, abstracted data from papers and commented on the analysis and interpretation, ARN commented on the protocol, provided additional relevant articles, screened retrieved papers against inclusion criteria, appraised quality of papers, abstracted data from papers, and was involved in discussing the findings, interpreting the data, and writing up. RAR helped design the review, screen retrieved papers against inclusion criteria, appraise quality of papers, and interpret the data, provided general advice, and commented on the analysis and interpretation. CDS helped design the review, screen retrieved papers against inclusion criteria, appraise quality of papers, and abstract data from papers, and commented on the analysis and interpretation. RLT helped design the review, screen retrieved papers against inclusion criteria, appraise quality of papers, abstract data frompapers, provide general advice, and comment on the analysis and interpretation. HVW helped in the analysis and interpretation of the data and provided a methodological and statistical perspective and general advice. LH is guarantor.

  • Funding A northwest research and development research fellowship (UK Department of Health) and the British Dietetic Association.

  • Competing interests NC has received fees for speaking by Solvay Healthcare, who market Omacor.

  • Ethical approval Not required.

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