GRADE assessment.

Background
Acute respiratory infections (ARIs) have a substantial impact on morbidity, healthcare utilization, and functional decline among older adults. Therefore, we systematically reviewed evidence from randomized controlled trials (RCTs) to evaluate the efficacy and safety of vitamin D supplementation in preventing ARIs in older adults.
Methods
PubMed, Embase, the Cochrane Library, and ClinicalTrials.gov were searched until 1 February 2024. RCTs evaluating the use of vitamin D supplements to protect older adults from ARIs were included. Two reviewers independently screened papers, extracted the data and assessed the risk of bias. Data were summarised as relative risks (RRs) or odds ratios (ORs) with corresponding 95% confidence intervals (CIs). Random effects meta-analyses were used to synthesise the results. GRADE was used to evaluate the quality of evidence. All the analysis were performed with Stata version 17.
Results
Twelve trials (41552 participants) were included in the meta-analysis. It showed that vitamin D supplementation probably does not reduce the incidence of ARIs (RR, 0.99; 95% CI, 0.97–1.02, I2 = 0%; moderate certainty). No significant effect of vitamin D supplementation on the risk of ARI was observed for any of the subgroups defined by baseline 25(OH)D concentration, control treatments, dose frequency, study duration, and participants’ condition. However, there was a possibility, although not statistically significant, that vitamin D may reduce the risk of ARI in patients with a baseline 25(OH)D concentration <50 nmol/L (OR, 0.90; 95% CI, 0.79–1.04, I2 = 14.7%). Additionally, vitamin D supplements might result in little to no difference in death due to any cause, any adverse event, hypercalcinemia, and kidney stones.
Conclusions
Vitamin D supplementation among older adults probably results in little to no difference in the incidence of ARIs. However, further evidence is needed, particularly for individuals with vitamin D deficiency and populations residing in low and middle income countries.
Trial registration
This study was registered on PROSPERO (CRD42023451265).

背景
急性呼吸道感染（acute respiratory infections, ARIs）对老年人的发病率、医疗资源利用及功能衰退具有显著影响。为此，本研究通过系统综述随机对照试验（randomized controlled trials, RCTs）的相关证据，评估补充维生素D对老年人预防急性呼吸道感染的有效性与安全性。
方法
检索截至2024年2月1日的PubMed、Embase、Cochrane图书馆及ClinicalTrials.gov数据库。纳入评估补充维生素D以保护老年人免受急性呼吸道感染的随机对照试验。由两名研究者独立完成文献筛选、数据提取及偏倚风险评估。研究数据以相对风险（relative risks, RRs）、比值比（odds ratios, ORs）及对应的95%置信区间（confidence intervals, CIs）进行汇总统计。采用随机效应模型Meta分析对研究结果进行合并。采用GRADE分级工具（Grading of Recommendations Assessment, Development and Evaluation, GRADE）评估证据质量。所有数据分析均采用Stata 17统计软件完成。
结果
本Meta分析共纳入12项试验，涉及41552名受试者。分析结果显示，补充维生素D或许并不能降低急性呼吸道感染的发病率（相对风险RR=0.99，95%置信区间CI：0.97~1.02，I²=0%，证据确定性等级为中等）。按基线25(OH)D浓度、对照干预措施、给药频率、研究时长及受试者基础健康状况划分的所有亚组中，均未观察到补充维生素D对急性呼吸道感染发病风险存在显著影响。不过，对于基线25(OH)D浓度＜50nmol/L的受试者，补充维生素D或可降低其急性呼吸道感染发病风险，尽管该差异未达到统计学显著性（比值比OR=0.90，95%置信区间CI：0.79~1.04，I²=14.7%）。此外，补充维生素D对全因死亡、任意不良事件、高钙血症及肾结石的发生风险均无显著影响，或仅存在极小差异。
结论
老年人补充维生素D或许对急性呼吸道感染的发病率无显著影响，或仅存在极小差异。不过仍需更多高质量研究证据，尤其是针对维生素D缺乏人群及低收入和中等收入国家的研究人群。
试验注册
本研究已在PROSPERO平台注册，注册号为CRD42023451265。