The effect of vitamin C supplementation on lipid profile of type 2 diabetic patients: a systematic review and meta-analysis of clinical trials

BACKGROUND AND AIMS: We conducted a systematic review and meta-analysis of clinical trials evaluating the role of vitamin C supplementation on lipid profiles among diabetic patients to summarize the available findings. METHODS: A comprehensive search of PubMed, ScienceDirect, Google Scholar, and Cochrane Library databases was performed. Clinical trials conducted on adult type 2 diabetic patients evaluating the effect of vitamin C supplementation and reported lipid profiles (cholesterol (TC), triglycerides (TG), low density lipoprotein (LDL), high density lipoprotein (HDL)) were included. Weighted mean difference (WMD) was calculated. RESULTS: Vitamin C supplementation had no significant effect on TC (WMD = − 4.36 mg/dl (95% CI − 10.24, 1.52) p-value = 0.146), LDL level (WMD = 2.73 mg/dl (95% CI − 1.72, 7.17) p-value = 0.229), and HDL level (WMD = 0.91 mg/dl (CI − 0.45, 2.27) p-value = 0.191). However, it reduced TG and secondary outcomes (FBS and HgA1C): TG (WMD = − 11.15 mg/dl (95% CI − 21.58, − 0.71) p-value = 0.036), FBS (WMD = − 16.94 mg/dl CI − 21.84, − 12.04, p-value = 0.000), and HgA1C (WMD = − 1.01% CI − 1.18, − 0.83, p-value = 0.001. Subgroup analysis also depicted younger patients, longer duration of treatment and higher dose were important factors. In addition, meta-regression analysis indicated the significant role of patient age, duration of treatment, supplementation dose, BMI and other baseline variables. CONCLUSION: There is no adequate evidence to support vitamin C supplementation for dyslipidemias in diabetic patients. Specific group of patients might have benefited including younger diabetic patients. Future researches should give emphasis on the duration of treatment, the dose of vitamin C and baseline values. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13098-021-00640-9.