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 .
FFA-induced endothelial dysfunction can be corrected by vitamin C.
Insulin resistance is associated with an inappropriate elevation of plasma FFA and endothelial dysfunction . FFA could stimulate formation of reactive oxygen species , which could be responsible for vascular impairment . In this r and omized , double-blind , cross-over study in 10 healthy volunteers ( 24 + /- 3 yr old ) , forearm blood flow ( FBF ) responses to intraarterial acetylcholine ( ACh ) and glyceryl trinitrate were assessed with coadministration of vitamin C ( 24 mg/ml ) or placebo , respectively , in the presence of increased plasma FFA induced by Intralipid/heparin infusion . The rise in plasma FFA from 320 + /- 64 to 1852 + /- 232 micromol/liter was associated with a reduced response of FBF to ACh by 55 % ( P < 0.01 ) . During coadministration of vitamin C , the impaired responsiveness of FBF to ACh was completely reversed and not different from that observed under baseline conditions . Vitamin C did not affect plasma FFA concentrations . Glyceryl trinitrate responsiveness was unchanged during FFA elevation , with or without vitamin C. These data suggest that FFA-induced vascular oxidative stress could contribute to endothelial dysfunction in insulin-resistant patients . High concentrations of antioxidants are able to reverse the local effects of FFA on endothelium-dependent vasodilation
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 .