Vitamin D insufficiency and deficiency are associated with a higher level of serum uric acid: A systematic review and meta-analysis

<b>Introduction/objectives:</b> Several epidemiological studies have suggested that patients with vitamin D insufficiency and deficiency tend to have a higher level of serum uric acid compared with those with adequate vitamin D level although the results were inconsistent across the studies. The current systematic review and meta-analysis was conducted with the aim to summarize all the available data. <b>Methods:</b> A systematic review was conducted using MEDLINE and EMBASE database from inception to May 2018 to identify all studies that compared the level of serum uric acid between individuals with normal vitamin D level and patients with vitamin D insufficiency/deficiency. Eligible studies must be cohort or cross-sectional studies that consisted of two groups of adult participants, one with normal level of vitamin D (vitamin D level &gt;30 ng/ml) and one with vitamin D insufficiency (vitamin D level 20–30 ng/ml) or vitamin D deficiency (vitamin D level of &lt;20 ng/ml). Mean serum uric acid level and standard deviation of participants were extracted from each study to calculate mean difference (MD). Pooled MD was then calculated by combining MDs of each study using random-effects model. <b>Results:</b> A total of seven cross-sectional studies were eligible for the meta-analyses. Individuals with normal vitamin D level had a significantly lower serum uric acid level than patients with vitamin D insufficiency with the pooled MD of –0.33 mg/dl (95%CI, –0.61, –0.04), and also had a significantly lower serum uric acid level than patients with vitamin D deficiency with the pooled MD of –0.45 mg/dl (95%CI, –0.82, –0.08). The statistical heterogeneity of these meta-analyses was high with the <i>I</i>² of 78% and 89%, respectively. Funnel plots of both meta-analyses were fairly symmetric and did not provide a suggestive evidence for the presence of publication bias. <b>Conclusion:</b> Both patients with vitamin D insufficiency and patients with vitamin D deficiency had a significantly higher level of serum uric acid compared with individuals with normal vitamin D level.

<b>引言/研究目的:</b> 多项流行病学研究提示，维生素D不足与缺乏患者的血清尿酸水平往往高于维生素D水平充足者，但不同研究的结果并不一致。本系统评价（systematic review）与荟萃分析（meta-analysis）旨在整合所有可用的相关研究数据。
<b>研究方法:</b> 本研究系统检索了MEDLINE与EMBASE数据库自建库至2018年5月的文献，以筛选所有对比维生素D水平正常者与维生素D不足/缺乏者血清尿酸水平的研究。纳入的研究需为队列研究或横断面研究，且包含两组成人受试者：一组为维生素D水平正常者（维生素D浓度＞30 ng/ml），另一组为维生素D不足者（维生素D浓度20~30 ng/ml）或维生素D缺乏者（维生素D浓度＜20 ng/ml）。从每项研究中提取受试者的平均血清尿酸水平与标准差，以计算均数差（mean difference, MD）。随后采用随机效应模型（random-effects model）合并各项研究的均数差，得到合并后的均数差。
<b>研究结果:</b> 共计7项横断面研究符合荟萃分析的纳入标准。与维生素D不足者相比，维生素D水平正常者的血清尿酸水平显著更低，合并均数差为-0.33 mg/dl（95%置信区间（95% confidence interval, 95%CI）：-0.61, -0.04）；与维生素D缺乏者相比，维生素D水平正常者的血清尿酸水平亦显著更低，合并均数差为-0.45 mg/dl（95%置信区间（95% confidence interval, 95%CI）：-0.82, -0.08）。两项荟萃分析的统计学异质性较高，I²分别为78%与89%。两项荟萃分析的漏斗图（funnel plots）均较为对称，未提示存在发表偏倚（publication bias）。
<b>研究结论:</b> 与维生素D水平正常者相比，维生素D不足与维生素D缺乏患者的血清尿酸水平均显著更高。