Effects of vitamin C supplementation on glycaemic control: a systematic review and meta-analysis of randomised controlled trials

Abstract

Randomised controlled trials (RCTs) have observed contrasting results on the effects of vitamin C on circulating biomarkers of glycaemic and insulin regulation. We conducted a systematic review and meta-analysis of RCTs testing the effect of vitamin C administration on glucose, HbA1c and insulin concentrations. Four databases (PubMed, Embase, Scopus and Cochrane Library) were used to retrieve RCTs published from inception until April 2016 and testing the effects of vitamin C in adult participants. The screening of 2008 articles yielded 22 eligible studies (937 participants). Overall, vitamin C did not modify glucose, HbA1c and insulin concentrations. However, subgroup analyses showed that vitamin C significantly reduced glucose concentrations (-0.44 mmol/l, 95% CI: -0.81, -0.07, P=0.01) in patients with type 2 diabetes and in interventions with a duration greater than 30 days (-0.53%, 95% CI: -0.79, -0.10, P=0.02). Vitamin C administration had greater effects on fasting (-13.63 pmol/l, 95% CI: -22.73, -4.54, P<0.01) compared to postprandial insulin concentration. 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. Personalised interventions with vitamin C may represent a feasible future strategy to enhance benefits and efficacy of interventions. Nevertheless, results need to be interpreted cautiously due to limitations in the primary studies analysed.

Ascorbic acid supplementation improves postprandial glycaemic control and blood pressure in individuals with type 2 diabetes: Findings of a randomized cross‐over trial

“…8 Improvements in insulin sensitivity with AA supplementation may subsequently promote improvements in glycaemic control. Indeed, findings of some studies, 7,[9][10][11][12] but not others, 13 support the efficacy of AA supplementation in improving glycaemic outcomes, including lowering of HbA1c and fasting glucose concentrations in individuals with T2D.…”

Vitamin C Inhibits Visceral Adipocyte Hypertrophy and Lowers Blood Glucose Levels in High-Fat-Diet-Induced Obese C57BL/6J Mice

“…Excess lipid accumulation in adipose tissues is promoted by a number of transcription factors, including PPARγ, SREBP-1c, and members of the CCAAT/enhancer-binding protein family (Ntambi et al, 2000;Rosen and MacDougald, 2006;Tang and Lane, 2012). These master regulators of adipogenesis and lipogenesis function by inducing transcription of targets such as SCD1, FAS, and acetyl-CoA carboxy-lase (Rosen and MacDougald, 2006;Strable and Ntambi, 2010 -Wahab et al, 2002;Garcia-Diaz et al, 2014;Ashor et al, 2017). Moreover, Williams et al (2016) reported that dietary supplementation with vitamins E and C attenuates dexamethasoneinduced glucose intolerance in rats.…”

Can vitamin C help in managing tuberculosis associated with diabetes mellitus?

“…11 In addition, diabetic subjects likely have increased requirement of vitamin C. 11 Several clinical studies have alluded to the improvement of glycaemic control in diabetics with vitamin C supplementation. 12 Importantly, low levels of vitamin C were also observed in some TB patients, 13 and in a sizable population-based cohort study, adequate dietary intake of vitamin C has been suggested to protect against developing active TB in current smokers. 14 Thus, it appears rewarding to consider exploration of the potential benefit of supplementation of this micronutrient in preventing active TB in diabetic subjects.…”