Effects of fish oil supplements in NIDDM subjects. Controlled study. The aim of this study was to evaluate the effects of a fish oil preparation (MaxEPA) on hemostatic function and fasting lipid and glucose levels in non-insulin-dependent diabetic (NIDDM) subjects. Eighty NIDDM outpatients aged 55.9 yr (mean SD 11.5 yr) participated in a prospective double-blind placebo-controlled study of MaxEPA capsules (10 g/day) or olive oil (control) treatment over 6 wk. Patients received either MaxEPA or olive oil in addition to preexisting therapy. Metabolic and hemostatic variables were measured before treatment and after 3 and 6 wk. Platelet membrane eicosapentaenoic acid (EPA) content increased in the treatment group (P less than 0.001). MaxEPA supplementation was associated with a significant fall in total triglycerides (P less than 0.001) but did not affect total cholesterol (P = 0.7) compared with control treatment. Fasting plasma glucose increased after 3 wk (P = 0.01) but not after 6 wk (P = 0.17) treatment with MaxEPA. Spontaneous platelet aggregation in whole blood fell in the MaxEPA group (P less than 0.02) after 6 wk, but there were no changes in agonist-induced platelet aggregation, thromboxane generation in platelet-rich plasma, or plasma beta-thromboglobulin and platelet factor IV levels. An increase in clotting factor VII (P = 0.02), without changes in fibrinogen or factor X levels, occurred in the MaxEPA group. Similar reductions in blood pressure were observed in both groups. Dietary supplementation with MaxEPA capsules (10 g/day) in NIDDM subjects is associated with improvement in hypertriglyceridemia but with deleterious effects in factor VII and blood glucose levels. Most indices of platelet function are unaffected by this therapy. 