Fish oil and glycemic control in diabetes - A meta-analysis

OBJECTIVE - Hypertriglyceridemia is associated with cardiovascular disease in diabetes. Fibrates effectively lower, but do not always normalize, serum triglyceride levels. Fish oil supplements may then be added to lower serum triglyceride levels. Doubt remains whether the net effect of fish oil intake on glycemic control is beneficial in diabetes. We therefore performed a meta-analysis from published clinical trials. RESEARCH DESIGN AND METHODS - Data sources were Medline (Cologne, Germany), Excerpta Medica, Current Contents, review articles, and published reference lists. Publications of 26 trials were selected, and all trials included more than five diabetes (IDDM and NIDDM) patients and addressed the effects of fish oil (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]) on serum lipids and glucose tolerance. We (C.E.F., M.J.F.M.J.) extracted data independently based on predetermined criteria. Studies were classified according to design. RESULTS - All studies combined showed a decrease in mean triglyceride concentrations in association with fish oil: -0.60 mmol/l (95% CI, -0.84 to -0.33, P < 0.01) and a slight but significant increase in serum LDL cholesterol: 0.18 mmol/l (95% CI, 0.04-0.32, P = 0.01), with both findings most prominent in NIDDM. No significant changes in HbA(1c) percentages occurred in diabetic subjects treated with fish oil. Fasting blood glucose levels were increased with borderline significance in NIDDM subjects (0.43 mmol/l [ 95% CI, 0.00 -0.87], P = 0.06) and were significantly lower in IDDM subjects (-1.86 mmol/l [95% CI, -3.1 to -0.61], P < 0.05). Significant dose-response effects of EPA (g/day) on HbA(1c) and triglycerides and of DHA (g/day) on fasting blood glucose levels, HbA(1c), and triglycerides were demonstrated only in NIDDM subjects. CONCLUSIONS - The use of fish oil has no adverse affects on HbA(1c) in diabetic subjects and lowers triglyceride levels effectively by almost 30%. However, this may be accompanied by a slight increase in LDL cholesterol concentration. Fish oil may be useful in treating dyslipidemia in diabetes.