Abstract：
Plasma 25-dihydroxyvitamin D levels appear reduced in patients with obesity or type 2 diabetes, as reported in several observational studies. However, the association between these reduced hormone levels and metabolic parameters is unclear. In any case, vitamin D supplementation in patients with Metabolic Syndrome is standard. Still, the impacts of this supplementation on conditions such as glycemia, blood pressure, and lipidemia are debatable. Based on this question, we carried out a systematic review and meta-analysis of randomized clinical trials in Brazil, Europe, and the United States that analyzed the effects of vitamin D supplementation on Metabolic Syndrome parameters in patients with obesity or type 2 diabetes. Our search yielded 519 articles and included 12 randomized controlled trials in the meta-analysis. Vitamin D supplementation had no effect on any of the outcomes analyzed (fasting blood glucose and insulinemia, glycated hemoglobin, HOMA index, systolic and diastolic blood pressure, weight, waist circumference, total cholesterol, LDL and HDL, and triglycerides). However, subgroup analyses indicated that using vitamin D up to 2000 IU daily reduced participants\' fasting blood glucose and glycated hemoglobin. Furthermore, the intervention reduced diastolic blood pressure only in participants with vitamin D deficiency. At least two studies showed a high risk of bias using the Rob2 protocol. According to the GRADE protocol, the evidence quality varied from moderate to very low. These results indicate that vitamin D supplementation does not improve patients\' metabolic parameters and that the association between plasma 25-dihydroxyvitamin D levels and Metabolic Syndrome may not be causal but caused by other confounding characteristics. However, in any case, the quality of evidence is still low, and more randomized clinical trials are essential to clarify these relationships.
摘要：
肥胖或2型糖尿病患者血浆25-二羟维生素D水平降低，正如一些观察性研究报告的那样。然而,这些降低的激素水平与代谢参数之间的关联尚不清楚.无论如何,代谢综合征患者补充维生素D是标准的。尽管如此，这种补充对血糖等疾病的影响，血压,和血脂是有争议的。基于这个问题,我们对巴西的随机临床试验进行了系统评价和荟萃分析，欧洲,和美国分析了补充维生素D对肥胖或2型糖尿病患者代谢综合征参数的影响。我们的搜索产生了519篇文章，并在荟萃分析中包括12项随机对照试验。补充维生素D对分析的任何结果均无影响（空腹血糖和胰岛素血症，糖化血红蛋白,HOMA指数,收缩压和舒张压,体重,腰围,总胆固醇,LDL和HDL,和甘油三酯）。然而,亚组分析显示,每天使用维生素D至2000IU可降低参与者的空腹血糖和糖化血红蛋白.此外，干预措施仅降低了维生素D缺乏参与者的舒张压。至少两项研究显示，使用Rob2方案的偏倚风险很高。根据GRADE协议,证据质量从中等到非常低。这些结果表明，补充维生素D不能改善患者的代谢参数，血浆25-二羟维生素D水平与代谢综合征之间的关联可能不是因果关系，而是由其他混杂特征引起的。然而,无论如何,证据质量仍然很低，和更多的随机临床试验是必要的，以澄清这些关系。
