Context: Type 2 diabetes (T2D) is one of the fastest-growing global health emergencies of the 21st century. However, high antioxidant capacity of supplementation of vitamin C and/or E was inversely associated with insulin resistance. However, each antioxidant possesses a distinct biological function that may be influenced by both dosage and duration of supplementation, potentially resulting in significantly different effects.
Objective: This meta-analysis aimed to evaluate whether vitamin C, vitamin E, or their combination is more effective in improving glycemic control, blood lipids, and blood pressure in individuals with T2D.
Data sources and data extraction: A systematic search was conducted in PubMed, Scopus, and Web of Science databases for randomized clinical trials, identifying 52 studies (n = 1425 participants).
Data analysis: Random-effects models were used to assess the effects of vitamin C and/or E supplementation on glycemic control, blood lipid levels, and blood pressure. These findings indicate that supplementation with vitamin C, vitamin E, or their combination has a comparable effect on glycemic index values, systolic blood pressure, and blood lipid profiles. However, a significant reduction in systolic blood pressure was observed only with vitamin C and combined vitamin C + E supplementation. Additionally, a significant increase in high-density-lipoprotein (HDL) levels was noted exclusively with the combined vitamin C + E supplementation.
Conclusion: Consequently, supplementation with vitamin C, vitamin E, and their combination (C + E) exhibited differing effects on HDL levels and systolic blood pressure. However, their effects on glycemic control, diastolic blood pressure, and blood lipids other than HDL were comparable.
Systematic review registration: PROSPERO registration no. CRD42023399366.
Keywords: HDL; alpha-tocopherol; ascorbic acid; systolic blood pressure.
© The Author(s) 2025. Published by Oxford University Press on behalf of the International Life Sciences Institute.