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


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


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.


CONCLUSIONS
Long chain and shorter chain omega 3 fats do not have a clear effect on total mortality, combined cardiovascular events, or cancer.
Hooper
Lee
L
School of Medicine, Health Policy and Practice, University of East Anglia, Norwich NR4 7TJ. l.hooper@uea.ac.uk
Thompson
Rachel L
RL
Harrison
Roger A
RA
Summerbell
Carolyn D
CD
Ness
Andy R
AR
Moore
Helen J
HJ
Worthington
Helen V
HV
Durrington
Paul N
PN
Higgins
Julian P T
JP
Capps
Nigel E
NE
Riemersma
Rudolph A
RA
Ebrahim
Shah B J
SB
Davey Smith
George
G
D002318:Cardiovascular Diseases / Q000401:mortality*; D015331:Cohort Studies; D019587:Dietary Supplements; D015525:Fatty Acids, Omega-3 / Q000008:administration & dosage*; D005395:Fish Oils; D006801:Humans; D009369:Neoplasms / Q000401:mortality*; D011379:Prognosis; D016032:Randomized Controlled Trials as Topic; D012307:Risk Factors
D015525:Fatty Acids, Omega-3; D005395:Fish Oils