Abstract: Background　Epidemiological surveys show that about 1 billion people worldwide suffer from vitamin D deficiency，which is particularly serious in China.Recurrent upper respiratory tract infection （URTI），with vitamin D deficiency a trigger，is a common and frequently-occurring disease in children，seriously affecting their physical and mental health.Vitamin D deficiency is the main reason for the down regulation of LL-37.As an important incentive，vitamin D deficiency has drawn more and more attention.Objective　To explore the changes in LL-37 level in children with recurrent URTI after vitamin D supplementation.Methods　54 children with recurrent URTI and vitamin D deficiency were selected from the outpatient clinic of Affiliated Hospital of Hebei University from May to November 2017.They were equally randomized into the experimental group and control group，receiving regular treatment with vitamin D supplementation，regular treatment with placebo，respectively.All of them were followed up for 12 months.Episodes of URTI before treatment and during the follow-up period，plasma 25-hydroxyvitamin D3 and LL-37 in sputum supernatant before treatment and at the end of the follow-up were measured and recorded.Results　Forty-five cases completed the follow-up （23 in the experimental group，and 22 in the control group）.Before treatment，both groups showed no significant differences in episodes of URTI，plasma 25-hydroxyvitamin D3 and LL-37 in sputum supernatant （P>0.05）.After 12 months of treatment，episodes of URTI were less，and plasma 25-hydroxyvitamin D3 and LL-37 in sputum supernatant were much higher in the experimental group （P<0.05）.Self-controlled comparisons showed that episodes of URTI，plasma 25-hydroxyvitamin D3 and LL-37 in sputum supernatant changed insignificantly in the control group （P>0.05），while episodes of URTI decreased，and plasma 25-hydroxyvitamin D3 and LL-37 in sputum supernatant increased significantly in the experimental group （P<0.05）.Pearson correlation analysis showed that there was a positive correlation between 25-hydroxyvitamin D3 and LL-37 after one-year treatment in the experimental group （r=0.505，P<0.05）.Conclusion　Vitamin D supplementation helps reduce the possibilities of having recurrent URTI，which may be associated with the increase in LL-37 production.

Key words: Respiratory tract infections, Vitamin D, Child, LL-37, Treatment outcome

摘要： 背景　流行病学调查显示全球大约有10亿人存在维生素D缺乏或不足，我国维生素D缺乏尤为严重。反复上呼吸道感染作为小儿常见病及多发病，严重影响小儿身心健康，维生素D缺乏是导致抗菌肽LL-37下调的主要原因，因此维生素D缺乏越来越引起人们的重视。目的　探讨反复上呼吸道感染患儿补充维生素D后LL-37水平变化。方法　选取2017年5—11月河北大学附属医院门诊就诊的反复上呼吸道感染并存在维生素D不足或缺乏的患儿54例，采用随机数字表法分为试验组及对照组，每组各27例。试验组给予常规治疗联合补充维生素D，对照组给予常规治疗联合安慰剂，随访12个月，记录治疗前和治疗后12个月时上呼吸道感染次数，检测血浆25-羟维生素D3及痰上清LL-37的变化。结果　45例患儿完成了随访，试验组23例，对照组22例。治疗前，两组患儿上呼吸道感染次数、血浆25-羟维生素D3及痰上清LL-37水平比较，差异均无统计学意义（P>0.05）；治疗后12个月，试验组患儿上呼吸道感染次数少于对照组，血浆25-羟维生素D3、痰上清LL-37水平高于对照组（P<0.05）。对照组患儿治疗前后上呼吸道感染次数、血浆25-羟维生素D3及痰上清LL-37水平比较，差异均无统计学意义（P>0.05）；试验组患儿治疗后12个月上呼吸道感染次数少于治疗前，血浆25-羟维生素D3、痰上清LL-37水平高于治疗前（P<0.05）。Pearson直线相关分析结果显示，试验组治疗后12个月血浆25-羟维生素D3与痰上清LL-37呈正相关（r=0.505，P<0.05）。结论　补充维生素D有助于减少反复上呼吸道感染患儿上呼吸道感染次数，这种作用可能与LL-37产生增加有关。

关键词: 呼吸道感染, 维生素D, 儿童, LL-37, 治疗结果