BACKGROUND: n-3 Fatty acids lower blood pressure, improve lipids, and benefit other cardiovascular disease risk factors. Effects on glycemia in patients with type 2 diabetes are uncertain.

OBJECTIVE: We determined whether purified eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have differential effects on glycemic control, including insulin sensitivity and stimulated insulin secretion; 24-h ambulatory blood pressure; and serum lipids in type 2 diabetic patients with treated hypertension.

DESIGN: In a double-blind, placebo-controlled trial of parallel design, 59 subjects were randomly assigned to consume 4 g EPA, DHA, or olive oil/d for 6 wk while continuing to consume their usual diet.

RESULTS: Thirty-nine men and 12 postmenopausal women with a mean (+/- SE) age of 61.2 +/- 1.2 y completed the study. In comparison with the change from baseline in fasting glucose in the olive oil group, fasting glucose in the EPA and DHA groups increased 1.40 +/- 0.29 mmol/L (P = 0.002) and 0.98 +/- 0.29 mmol/L (P = 0.002), respectively. Neither EPA nor DHA had significant effects on glycated hemoglobin, fasting insulin or C-peptide, insulin sensitivity or secretion, or blood pressure. Serum triacylglycerols in the EPA and DHA groups decreased 19% (P = 0.022) and 15% (P = 0.022), respectively. There were no significant changes in serum total, LDL, or HDL cholesterol, although HDL(2) cholesterol in the EPA and DHA groups increased 16% (P = 0.026) and 12% (P = 0.05), respectively. HDL(3) cholesterol decreased 11% (P = 0.026) with EPA supplementation.

CONCLUSIONS: EPA and DHA had similar benefits on lipids but adverse effects on short-term glycemic control in hypertensive diabetic patients. The overall implications for cardiovascular disease require long-term evaluation.