Prolonged antioxidant vitamin E and /or C supplementation could be effective to improve endothelial function in non-obese T2DM subjects
Controversy exists among trials assessing whether prolonged antioxidant vitamin supplementation improves endothelial function in type 2 diabetes mellitus ( T2DM ) subjects .
The aim of this study was to systematic ally review and quantify the effect of antioxidant vitamin supplementation on endothelial function in T2DM subjects .
High-dose oral vitamin C partially replenishes vitamin C levels in patients with Type 2 diabetes and low vitamin C levels but does not improve endothelial dysfunction or insulin resistance.
Endothelial dysfunction is a hallmark of Type 2 diabetes related to hyperglycemia and oxidative stress . Nitric oxide-dependent vasodilator actions of insulin may augment glucose disposal . Thus endothelial dysfunction may worsen insulin resistance . Intra-arterial administration of vitamin C improves endothelial dysfunction in diabetes . In the present study , we investigated effects of high-dose oral vitamin C to alter endothelial dysfunction and insulin resistance in Type 2 diabetes .  Plasma vitamin C levels in 109 diabetic subjects were lower than healthy ( 36 + /- 2 microM ) levels . Thirty-two diabetic subjects with low plasma vitamin C ( < 40 microM ) were subsequently enrolled in a r and omized , double-blind , placebo-controlled study of vitamin C ( 800 mg/day for 4 wk ) . Insulin sensitivity ( determined by glucose clamp ) and forearm blood flow in response to ACh , sodium nitroprusside ( SNP ) , or insulin ( determined by plethysmography ) were assessed before and after 4 wk of treatment . In the placebo group ( n = 17 subjects ) , plasma vitamin C ( 22 + /- 3 microM ) , fasting glucose ( 159 + /- 12 mg/dl ) , insulin ( 19 + /- 7 microU/ml ) , and SI(Clamp ) [ 2.06 + /- 0.29 x 10(-4 ) dl x kg(-1 ) x min(-1)/(microU/ml ) ] did not change significantly after placebo treatment . In the  vitamin C  group ( n = 15 subjects ) , basal plasma vitamin C ( 23 + /- 2 microM ) increased to 48 + /- 6 microM ( P < 0.01 ) after treatment , but this was significantly less than that expected for healthy subjects ( > 80 microM ) . No significant changes in fasting glucose ( 156 + /- 11 mg/dl ) , insulin ( 14 + /- 2 microU/ml ) , SI(Clamp ) [ 2.71 + /- 0.46 x 10(-4 ) dl x kg(-1 ) x min(-1)/(microU/ml ) ] , or forearm blood flow in response to ACh , SNP , or insulin were observed after vitamin C treatment . We conclude that high-dose oral vitamin C therapy , result ing in incomplete replenishment of vitamin C levels , is ineffective at improving endothelial dysfunction and insulin resistance in Type 2 diabetes
Prolonged antioxidant vitamin E and /or C supplementation could be effective to improve endothelial function in non-obese T2DM subjects
Controversy exists among trials assessing whether prolonged antioxidant vitamin supplementation improves endothelial function in type 2 diabetes mellitus ( T2DM ) subjects .
The aim of this study was to systematic ally review and quantify the effect of antioxidant vitamin supplementation on endothelial function in T2DM subjects .