Effects of Vitamin C Supplementation on Glycemic Control and Cardiovascular Risk Factors in People With Type 2 Diabetes: A GRADE-Assessed Systematic Review and Meta-analysis of Randomized Controlled Trials

Study answer

What this study found

Vitamin C supplementation produced statistically significant improvements in HbA1c (−0.54 percentage points) and fasting glucose (−0.74 mmol/L), and decreased systolic BP (−6.27 mmHg) and diastolic BP (−3.77 mmHg). Triglycerides (−0.20 mmol/L) and total cholesterol (−0.27 mmol/L) decreased; LDL cholesterol showed no significant change (−0.23 mmol/L; P=0.08); HDL cholesterol rose slightly (0.06 mmol/L; P=0.06). Plasma malondialdehyde decreased (standardized MD −1.25). Some lipid/oxidative markers showed no significant change. Overall certainty for primary outcomes ranged from very low to…

Study & population

Adults with type 2 diabetes; randomized controlled trials (including parallel and crossover designs); 28 trials with 1,574 participants; data extracted by two independent reviewers; risk of bias assessed; evidence certainty rated with GRADE.

Intervention

Oral vitamin C supplementation; regimens included 1,000 mg/day (commonly) and 500 mg/day in some trials; durations varied from short-term (<6 months) to longer-term (≥12 weeks); taken daily.

Key limitation

Predominantly short-term (<6 months) trials with small sample sizes; substantial heterogeneity and risk-of-bias concerns; dosing and duration of vitamin C varied across studies; many trials included concomitant diabetes therapies; adverse events rarely or inconsistently reported; potential publication bias and…

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Original abstract