Context:

Clinical trials report differing effects of omega-3 fatty acids on lipids and glycemic control in type II diabetes and the metabolic syndrome and on inflammatory bowel disease (IBD), rheumatic arthritis, renal disease, systemic lupus erythemosus (SLE), and osteoporosis.

Objectives:

To assess the effect of omega-3 fatty acids on 1) total cholesterol, LDL cholesterol, HDL cholesterol, triglycerides, and insulin resistance in type-II diabetes and the metabolic syndrome, 2) clinical score, sigmoidoscopic score, histologic score and requirement for immunosuppressive therapy in IBD, 3) pain, swollen and tender joint counts, acute phase reactants, patient global assessment, and requirement for anti-inflammatory or immunosuppressive therapy in rheumatoid arthritis, 4) renal function, progression to end-stage renal disease, hemodialysis graft patency, mortality, and requirement for immunosuppressive therapy in renal disease, 5) disease activity, damage, patient's perception of disease activity, and requirement for immunosuppressive therapy in SLE, and 6) bone mineral density and fracture rates.

Data Sources:

We searched on-line databases to identify potentially relevant studies and contacted industry experts for unpublished data.

Study Selection:

We screened 4,212 titles, reviewed 1,097 articles, and included 83 articles. We restricted to randomized controlled trials (RCTs), but included case-control and cohort studies for bone/fracture. We had no language restrictions.

Data Extraction:

We abstracted data on study design, study population, and outcomes; source, amount, and duration of omega-3 fatty acid consumption; and randomization, dropouts, blinding, and allocation for RCTs.

Data Synthesis:

We performed meta-analyses for diabetes, rheumatoid arthritis, and IBD; and qualitative analyses for the other conditions.

For diabetes, omega-3 fatty acids had a favorable effect on triglyceride levels but no significant effect on total cholesterol, HDL cholesterol, LDL cholesterol, fasting blood sugar, or glycosylated hemoglobin. There was no effect on plasma insulin or insulin resistance in type II diabetics or the metabolic syndrome.

For IBD, omega-3 fatty acids had variable effects on clinical score, sigmoidoscopic score, histologic score, induced remission, and relapse, and no effect on the relative risk of relapse in ulcerative colitis. There was a statistically non-significant reduction in requirement for corticosteroids. No studies evaluated requirement for other immunosuppressive agents.

For rheumatoid arthritis, omega-3 fatty acids had no effect on patient report of pain, swollen joint count, Erythrocyte Sedimentation Rate, and patient's global assessment. There was no effect on joint damage, contrary to a previous meta-analysis. There was a reduced requirement for anti-inflammatory drugs or corticosteroids. No studies assessed requirements for disease modifying antirheumatic drugs.

For renal disease, omega-3 fatty acids had varying effects on serum creatinine and creatinine clearance. Single studies respectively demonstrated reduced progression to end-stage renal disease and improvements on hemodialysis graft patencyrelative. No studies assessed requirements for corticosteroids or other immunosuppressive drugs.

For SLE, omega-3 fatty acids had variable effects on clinical activity. No studies assessed the effect on end organ damage, patient perception of disease, or requirements for other immunosuppressive drugs. One study showed no effect on corticosteroid requirements.

For bone mineral density, the effect of omega-3 fatty acids was variable. No studies assessed the effect on fracture.

Conclusions:

The evidence for effects of omega-3 fatty acids on outcomes in the conditions assessed varies greatly. Omega-3 fatty acids appear to reduce serum triglycerides among type II diabetics, but have no effect on total cholesterol, HDL cholesterol, and LDL cholesterol. There appears to be no effect on most clinical outcomes in rheumatoid arthritis, although tender joint count may be reduced. There are insufficient data to draw conclusions about IBD, renal disease, SLE, bone density or fractures, requirement for anti-inflammatory or immunosuppressive drugs, or insulin resistance among type II diabetics.