['Endothelial dysfunction and arterial stiffening are commonly observed in type 2 diabetes. These abnormalities might be secondary to increased plasma concentrations of homocysteine. We sought to determine whether oral folic acid supplementation, by lowering homocysteine levels, enhanced endothelial function and reduced arterial stiffness in type 2 diabetes.', 'Twenty-six type 2 diabetic patients (age 56.5 +/- 0.9 years, diabetes duration 5.5 +/- 0.6 years, means +/- SEM) with no history of cardiovascular disease received 5 mg/d of oral folic acid or placebo for 4 weeks in a double-blind, randomized controlled, parallel group trial. The following parameters were measured before and after treatment: 1) endothelial function (forearm arterial blood flow during local intra-arterial administration of endothelium-dependent [acetylcholine 1.5, 4.5, and 15 microg/min] and endothelium-independent [sodium nitroprusside 1, 2, and 4 microg/min] vasodilators); and 2) carotid-radial and carotid-femoral pulse wave velocity.', 'Folic acid reduced plasma homocysteine concentrations and enhanced endothelium-dependent vasodilatation during each acetylcholine infusion rate (mean and 95% confidence interval post versus pretreatment differences in forearm arterial blood flow ratio between the infused and control arm +0.19 (0.03-0.35), P < .01; +0.39 (0.02-0.81), P < .05; and +0.40 (0.09-0.89), P < .05, respectively). Endothelium-independent vasodilatation and pulse wave velocity were not affected. No significant changes in forearm arterial blood flow and pulse wave velocity were observed in the placebo group. Multiple regression analysis showed that changes in folic acid, but not homocysteine, concentrations independently described changes in maximal endothelium-dependent vasodilatation.'] Does short-term oral folic acid supplementation enhance endothelial function in patients with type 2 diabetes?