Antioxidant effects of vitamins in type 2 diabetes: A meta-analysis of randomized controlled trials.

Type 2 diabetes is associated with increased oxidative stress, and low concentrations of antioxidants might increase the risk of diabetic complications. Randomized controlled trials that have evaluated antioxidant supplementation in type 2 diabetes, however, have produced mixed results. To better understand whether antioxidant supplementation might benefit patients with type 2 diabetes, researchers conducted a systematic review and meta-analysis.

Methods

A total of 31 randomized controlled trials were identified for the review. All studies were conducted in adult participants with any stage of type 2 diabetes. The interventions were vitamin B, vitamin C, vitamin D, vitamin E, or a mixture of vitamins B, C, and E. Study durations ranged from 2 to 24 weeks. Outcomes included blood parameters of oxidative stress or blood sugar regulation.

Low concentrations of antioxidants might increase the risk of diabetic complications.

Results

Twelve studies were included in the meta-analysis. Results showed that vitamins C and E were associated with higher glutathione peroxidase (GPx), superoxide dismutase (SOD), and total antioxidant capacity (TAC) when compared with placebo. Vitamins C and E were also associated with reduced malondialdehyde (MDA) and thiobarbituric acid reactive substances (TBARS), which are end-products of lipid peroxidation. Vitamin E was associated with a significant reduction of blood glucose and glycosylated hemoglobin (HbA1c) when compared with placebo. No significant effects were found for vitamins B or D.   

Conclusions

Overall, these results suggest that vitamin E supplementation might support healthier parameters of antioxidant status and glycemic control in patients with type 2 diabetes. Vitamin C might provide additional antioxidant support. The dosages for vitamin E ranged from 400 to 1600 IU/day, and the dosages of vitamin C ranged from 500 to 3000 mg/day. 

Although these results are promising, this meta-analysis has some limitations. It included a small number of studies, and each of the studies included a small number of participants. Also, the methodology of the included trials was deemed to be only low-to-moderate quality, with questionable randomization and blinding. Further research is needed to fully understand whether antioxidant supplementation can support healthier metabolism and reduce the risk of complications in patients with diabetes.

Balbi, M. E., Tonin, F. S., Mendes, A. M., Borba, H. H., Wiens, A., Fernandez-Llimos, F., & Pontarolo, R. (2018). Antioxidant effects of vitamins in type 2 diabetes: A meta-analysis of randomized controlled trials. Diabetology & Metabolic Syndrome10, 18.