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 .
Effects of vitamins C and E and beta-carotene on the risk of type 2 diabetes in women at high risk of cardiovascular disease: a randomized controlled trial.
BACKGROUND Vitamin C , vitamin E , and beta-carotene are major antioxidants and as such may protect against the development of type 2 diabetes via reduction of oxidative stress . OBJECTIVE The purpose of this study was to investigate the long-term effects of supplementation with vitamin C , vitamin E , and beta-carotene for primary prevention of type 2 diabetes . DESIGN In the Women 's Antioxidant Cardiovascular Study , a r and omized trial that occurred between 1995 and 2005 , 8171 female health professionals aged > or = 40 y with either a history of cardiovascular disease ( CVD ) or > or =3 CVD risk factors were r and omly assigned to receive vitamin C ( ascorbic acid , 500 mg every day ) , vitamin E ( RRR-alpha-tocopherol acetate , 600 IU every other day ) , beta-carotene ( 50 mg every other day ) , or their respective placebos . RESULTS During a median follow-up of 9.2 y , a total of 895 incident cases occurred among 6574 women who were free of diabetes at baseline . There was a trend toward a modest reduction in diabetes risk in women assigned to receive vitamin C compared with those assigned to receive placebo [ relative risk ( RR ) : 0.89 ; 95 % CI : 0.78 , 1.02 ; P = 0.09 ] , whereas a trend for a slight elevation in diabetes risk was observed for vitamin E treatment ( RR : 1.13 ; 95 % CI : 0.99 , 1.29 ; P = 0.07 ) . However , neither of these effects reached statistical significance . No significant effect was observed for beta-carotene treatment ( RR : 0.97 ; 95 % CI : 0.85 , 1.11 ; P = 0.68 ) . CONCLUSION Our r and omized trial data showed no significant overall effects of vitamin C , vitamin E , and beta-carotene on risk of developing type 2 diabetes in women at high risk of CVD . This trial was registered at clinical trials.gov as NCT00000541
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 .