Influence of Ascorbic Acid Supplementation on Type 2 Diabetes Mellitus in Observational and Randomized Controlled Trials; A Systematic Review with Meta-Analysis

Abstract

-Purpose.There are controversial data regarding the beneficial effects of ascorbic acid (AA) supplementation in type 2 diabetes mellitus (T2DM). In this systematic review, we aimed to criticize the current relevant data from both observational and randomized controlled trials (RCTs). Methods. All observational and RCTs conducted to assess anti-hyperglycemic effects of AA in diabetics, published before January 2013, were included. To obtain all related studies Google Scholar, PubMed, Scopus, IranMedex, and Magiran web databases were searched. Exclusion criteria were animal studies, and studies conducted in Type 1 DM, children or pregnant women. Main outcome measures were fasting blood sugar (FBS), and glycated hemoglobin (HbA1c). According to degree of heterogeneity, fixed or random effect models were employed. Meta-analyses were done using Stats Direct software, version 3.0.97. The quality of included articles and publication bias were also assessed. Results. We selected 38 articles; 26 observational studies and 12 RCTs. Due to severe methodological heterogeneity in all observational studies and some of RCTs, we could pool data from only 5 RCTs in a meta-analysis. Single intake of AA versus placebo showed a significant effect on FBS; with the standardized mean difference (SMD): -20.59, 95% confidence intervals (95% CI): -40.77 to -0.4 (p= 0.04), but non-significant effect on HbA1c; SMD: -0.46, 95% CI: -1.75 to 0.84 (p= 0.4). Effect of other antioxidants with/without AA supplementation on FBSwere nonsignificant; SMD: -4.26 (p= 0.8), and SMD: -12.04 (p= 0.3), respectively. Also, their effect on HbA1c was non-significant; SMD: 0.53 (p= 0.11), and SMD: 0.28 (p= 0.34), respectively. Conclusions. Our study supports the positive effect of AA in reduction of FBS in diabetics, however, due to insufficient evidence ragarding long term safety of AA supplementation and limited number of RCTs, the long term use of this vitamin for its anti-diabetic properties cannot be strongly recommended.

Effect of vitamins C and E on insulin resistance in diabetes: a meta‐analysis study

“…In addition, the protective effect of VC against NO was not observed in subjects with diabetes , which may indicate that VC produces beneficial effects when administered during the early onset of CVD . Our results are in line with the results of meta‐analysis studies conducted with VE and VC supplementations in T2DM . The meta‐analysis of RCTs with VE supplementation in T2DM did not show any significant beneficial effects on HbA1c, fasting glucose and fasting insulin.…”

“…The meta‐analysis of RCTs with VE supplementation in T2DM did not show any significant beneficial effects on HbA1c, fasting glucose and fasting insulin. But, the meta‐analysis of RCTs with VC supplementation showed a significant beneficial effect on fasting glucose and a nonsignificant effect on HbA1c. In that study, pooling data of fasting insulin was impossible due to the less number of eligible studies.…”

Hormetic and regulatory effects of lipid peroxidation mediators in pancreatic beta cells

“…Meta-analyses of several clinical trials on the efficacy of different antioxidants have yet failed to provide sufficient evidence for beneficial effects of antioxidant supplementation in diabetes or other chronic diseases. Worrisome are some trials that were interrupted prematurely due to adverse effects of some antioxidants that appeared to increased mortality (Bjelakovic et al, 2007;Han et al, 2012;Khodaeian et al, 2015;Kim et al, 2015;Tabatabaei-Malazy et al, 2014).…”

Witamina C – budowa, właściwości, funkcje i występowanie

“…leków będących związkami aromatycznymi) [2], ȇ zwiększa przyswajanie żelaza niehemowego oraz wap nia -kwas askorbinowy redukuje żelazo(III) do żelaza(II) w jednoelektrodowej reakcji, samemu przekształcając się w kwas monodehydroaskorbinowy [2], co z kolei ma istotne RYCINA 4. Przemiany kwasu askorbinowego [12] znaczenie, ponieważ żelazo jest absorbowanie w dwunastnicy w postaci zredukowanej Fe(II) [16], ȇ jest niezbędna w przebiegu prawidłowej oksydatywnej degradacji tyrozyny [2], ȇ regeneruje tokoferol z jego postaci wolnorodnikowej [7], ȇ bierze udział w biosyntezie karnityny (kwasu 4 -N -trim etylo -3 -hydroksymasłowego) [2], ȇ bierze udział w odbudowie tkanek podczas gojenia się ran [17], ȇ reguluje ciśnienie tętnicze [17], ȇ pomaga w utrzymaniu zdrowych dziąseł [17], ȇ obniża stężenie glukozy we krwi w stanach hiperglike mii [17] oraz obniża poziomu cukru we krwi na czczo u chorych na cukrzycę [18].…”