Interventional prospective research design.~The study will be conducted on patients with moderate and severe COPD. The material for the study will be the blood and sputum of patients with COPD.~Research methods: biochemical, enzyme immunoassay, bacteriological, radiological, spirography, clinical, statistical analysis.~The recruitment of patients is carried out in the pulmonology department of the hospital according to the inclusion and exclusion criteria. Patient participation is voluntary. First, the patient is told about the study. If he agrees, he signs an informed consent to conduct research.~Clinical examination of the patient, anthropometry, standard COPD assessment tests will be conducted in the hospital.~Laboratory tests will be conducted in medical institutions in Karaganda and will include a detailed general blood test, determination of fibrinogen and CRP (C-reactive protein) levels, general sputum analysis and bacteriological sputum examination.~Instrumental studies are carried out in medical institutions of the city: spirometry (determination of FEV1 (forced exhalation volume), Gensler index and Tiffno), lung radiography.~The study of vitamin D and cathelicidin is carried out by the ELISA method in the laboratory of the Medical University. Assessment of vitamin D status will be carried out by determining the level of total 25(OH)D (circulating serum, total D2 and D3) with verification of the method relative to international standards (National Institute of Standards and Technology - National Institute of Standards and Technology (NIST), Vitamin D External Quality Assessment Scheme (DEQAS)). The interpretation of vitamin D levels will be carried out according to international standards:~less than 10 ng/ml severe deficiency; 10-20 ng/ml moderate deficiency; 20-30 ng/ml mild deficiency; 30-100 ng/ml Norm; more than 100 ng/ml toxic level.~Quantitative determination of the level of antimicrobial peptide cathelicidin (LL-37) in blood serum will be carried out using enzyme immunoassay (NK321, HumanLL-37 ELISA Kit, Hycult biotech, the Netherlands) in accordance with the manufacturer's instructions. . Normal levels of LL-37: 50-80 ng/ml.~Among the patients with COPD selected at the outpatient stage, persons with vitamin 25(OH) deficiency were identifiedD in the blood (insufficiency/deficiency). In this group, patients received a therapeutic dose of an aqueous solution of cholecalciferol for three months. The therapeutic dose of an aqueous solution of cholecalciferol will be calculated individually according to clinical recommendations for the treatment of vitamin D deficiency and insufficiency.~Patients will continue treatment of the underlying COPD disease according to the clinical protocol. Vitamin therapy is an addition to the main treatment, it should strengthen the immunity and protective abilities of the body. After three months of replacement therapy with cholecalciferol and the next 3 months without it, clinical, laboratory and instrumental research methods will be repeated to assess the effectiveness.~Statistical processing of the research results is supposed to be carried out using statistical packages Excel 2010 (Microsoft, USA), Statistica 10.0 (StatSoft, Inc., USA). Methods of parametric and nonparametric statistics will be used: Student's criterion (t), Mann-Whitney (U), Wilcoxon; correlation analysis with calculation of Spearman's correlation coefficient (R). To compare the case-control groups with a quantitative assessment of the relationship between the factor and the outcome, the odds ratio (OR) with 95% CI will be calculated.
Recruitment of patients with COPD. Assessment of clinical status, determination of vitamin D and cathelicidin levels. In the group with vitamin D deficiency, patients receive cholecalciferol (vitamin D) daily for 3 months. After 3 months, the clinical status was assessed again, the level of vitamin D and cathelicidin was determined. When vitamin D levels normalize, cholecalciferol replacement therapy is discontinued for 3 months. After that, a control inspection and laboratory tests are performed.