Mousa Aya
Published: 2017
Total Pages:
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BACKGROUND: Chronic low-grade inflammation is common in obesity and related chronic conditions, including type 2 diabetes. Vitamin D has been proposed to have anti-inflammatory properties; however the effect of vitamin D supplementation on inflammation in type 2 diabetes has not been established. AIM: We conducted a systematic review and meta-analysis to examine the effect of vitamin D supplementation on inflammatory markers compared to placebo or usual care in patients with type 2 diabetes, and to identify relevant knowledge gaps. METHODS: Medline, CINAHL, EMBASE and All EBM were systematically searched (from inception to 25 January 2017) for randomized controlled trials (RCTs) investigating the effects of vitamin D supplementation on inflammatory markers in type 2 diabetes patients. Two independent reviewers screened all full text articles (no date or language limits) for RCTs of vitamin D supplementation (any form, route, duration, and co-supplementation) compared to placebo or usual care on all inflammatory marker outcomes in patients with type 2 diabetes (on any treatment regimen and with or without comorbidities). Meta-analyses and meta-regression were conducted using random-effects models to calculate standardized mean differences (SMD) and 95%CIs. Two independent reviewers extracted data and assessed risk of bias and quality using the grading of recommendations, assessment, development and evaluation (GRADE) approach.RESULTS: Twenty-nine RCTs (n=1,780) met the inclusion criteria, 20 of which had available data for pooling. In meta-analyses of 20 RCTs (n=1,270), vitamin D-supplemented groups had lower follow-up levels of C-reactive protein (SMD: -0.23 mg/L (-0.37,-0.09); p=0.002), tumor necrosis factor-alpha (SMD: -0.49 pg/ml (-0.84,-0.15); p=0.005), and erythrocyte sedimentation rate (SMD: -0.47 mm/hr (-0.89,-0.05); p=0.03), and higher levels of leptin (SMD: 0.42 u00b5g/L (0.04, 0.81); p=0.03), compared to placebo. No differences were observed for adiponectin, interleukin-6, or E-selectin (all p>0.05). In meta-regression and subgroup analyses, age, sex, BMI, diabetes duration, baseline vitamin D status, and supplementation dose and duration did not alter the results. There was no evidence of heterogeneity (p>0.1) or publication bias (p>0.1) and most studies were low to moderate risk of bias. CONCLUSIONS: Our meta-analysis provides level one evidence that vitamin D supplementation may improve chronic low-grade inflammation in patients with type 2 diabetes. Further studies are needed to establish whether improved inflammation following vitamin D supplementation would translate into improved health outcomes for patients with type 2 diabetes. PROSPERO registration number: CRD42016047755.