BMJ  2006;332:752-760 (1 April), doi:10.1136/bmj.38755.366331.2F (published 24 March 2006)

Research

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

¹ School of Medicine, Health Policy and Practice, University of East Anglia, Norwich NR4 7TJ, ² Institute of Human Nutrition, University of Southampton, Southampton SO16 6YD, ³ Bolton Primary Care Trust, Bolton BL1 1PP, ⁴ School of Health and Social Care, University of Teesside, Middlesbrough TS1 3BA, ⁵ Department of Community-based Medicine, University of Bristol, Bristol BS8 1TQ, ⁶ Department of Social Medicine, University of Bristol, Bristol BS8 2PR, ⁷ School of Dentistry, University of Manchester, Manchester M15 6FH, ⁸ Department of Medicine, University of Manchester, ⁹ MRC Biostatistics Unit, Cambridge CB2 2SR, ¹⁰ Department of Clinical Biochemistry, Princess Royal Hospital, Shrewsbury and Telford Hospital NHS Trust, Telford TF1 6TF, ¹¹ Centre for Cardiovascular Science, University of Edinburgh, Edinburgh EH16 4TJ, ¹² London School of Hygiene and Tropical Medicine, London WC1E 7HT Department of Epidemiology and Population Health

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.

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