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 .
Vitamin C and hyperglycemia in the European Prospective Investigation into Cancer--Norfolk (EPIC-Norfolk) study: a population-based study.
OBJECTIVE To examine the cross-sectional association between plasma vitamin C , self-reported diabetes , and HbA1c . RESEARCH DESIGN AND METHODS Data from a population -based study of diet , cancer , and chronic disease were analyzed . A total of 2,898 men and 3,560 women 45 - 74 years of age who were registered with general practice s in Norfolk , U.K. , were recruited to the European Prospect i ve Investigation Into Cancer-Norfolk study between 1995 and 1998 . RESULTS Mean plasma vitamin C levels were significantly higher in individuals with HbA1c levels < 7 % than in those with self-reported diabetes or prevalent undiagnosed hyperglycemia ( HbA1c > or = 7 % ) . An inverse gradient of mean plasma vitamin C was found in both sexes across quintiles of HbA1c distribution < 7 % . The odds ratio ( 95 % CI ) of having prevalent undiagnosed hyperglycemia per 20 micromol/l ( or 1 SD ) increase in plasma vitamin C was 0.70 ( 0.52 - 0.95 ) ( adjusted for sex , age , BMI , waist-to-hip ratio , tertiary education , any use of dietary supplements , vegetarian diet , alcohol consumption , physical activity , dietary vitamin E , dietary fiber , dietary saturated fat , and smoking history ) . The unadjusted change in HbA1c per 20 micromol/l increase in vitamin C estimated by linear regression was -0.12 % ( -0.14 to -0.09 ) in men and -0.09 % ( -0.11 to -0.07 ) in women . After adjusting for the possible confounders , these values were -0.08 % ( -0.11 to -0.04 ) in men and -0.05 % ( -0.07 to -0.03 ) in women . CONCLUSIONS An inverse association was found between plasma vitamin C and HbA1c .  Dietary measures to increase  plasma vitamin C  may be an important public health strategy for reducing the prevalence of diabetes
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 .