Overall , vitamin C did not modify glucose , HbA1c and insulin concentrations .
Meta-regression analyses showed that age was a modifier of the effect of vitamin C on insulin concentration .
Furthermore , the effect size was associated with baseline BMI and plasma glucose levels , and with the duration of the intervention .
In conclusion , greater reduction in glucose concentrations observed in patients with diabetes , older individuals and with more prolonged supplementation .
R and omised controlled trials ( RCTs ) have observed contrasting results on the effects of vitamin C on circulating biomarkers of glycaemic and insulin regulation .
Long-term ascorbic acid administration reverses endothelial vasomotor dysfunction in patients with coronary artery disease.
BACKGROUND Loss of endothelium-derived nitric oxide ( EDNO ) contributes to the clinical expression of coronary artery disease ( CAD ) . Increased oxidative stress has been linked to impaired endothelial vasomotor function in atherosclerosis , and recent studies demonstrated that short-term ascorbic acid treatment improves endothelial function . METHODS AND RESULTS In a r and omized , double-blind , placebo-controlled study , we examined the effects of single-dose ( 2 g PO ) and long-term ( 500 mg/d ) ascorbic acid treatment on EDNO-dependent flow-mediated dilation of the brachial artery in patients with angiographically established CAD .  Flow-mediated dilation was examined by high-resolution vascular ultrasound at baseline , 2 hours after the single dose , and 30 days after long-term treatment in 46 patients with CAD .  Flow-mediated dilation improved from 6.6+/-3.5 % to 10.1+/-5.2 % after single-dose treatment , and the effect was sustained after long-term treatment ( 9 . 0+/-3.7 % ) , whereas flow-mediated dilation was 8.6+/-4.7 % at baseline and remained unchanged after single-dose ( 7.8+/-4.4 % ) and long-term ( 7.9+/-4.5 % ) treatment with placebo ( P=0.005 by repeated- measures ANOVA ) . Plasma ascorbic acid concentrations increased from 41.4+/-12 . 9 to 115.9+/-34.2 micromol/L after single-dose treatment and to 95 . 0+/-36.1 micromol/L after long-term treatment ( P<0.001 ) . CONCLUSIONS In patients with CAD , long-term ascorbic acid treatment has a sustained beneficial effect on EDNO action . Because endothelial dysfunction may contribute to the pathogenesis of cardiovascular events , this study indicates that ascorbic acid treatment may benefit patients with CAD
Overall , vitamin C did not modify glucose , HbA1c and insulin concentrations .
Meta-regression analyses showed that age was a modifier of the effect of vitamin C on insulin concentration .
Furthermore , the effect size was associated with baseline BMI and plasma glucose levels , and with the duration of the intervention .
In conclusion , greater reduction in glucose concentrations observed in patients with diabetes , older individuals and with more prolonged supplementation .
R and omised controlled trials ( RCTs ) have observed contrasting results on the effects of vitamin C on circulating biomarkers of glycaemic and insulin regulation .