Дисертація присвячена питанню підвищення ефективності профілактики розвитку повторних епізодів гострого обструктивного ларингіту. Обстежено 128 дітей віком від 4-х місяців до 3-х років із діагнозом «гострий обструктивний ларингіт».Встановлено, що частота рекурентних епізодів гострого обструктивного ларингіту зростає у дітей із обтяженим алергологічним анамнезом (до 46,4 %), із дисфункцією шлунково-кишкового тракту (до 41,1 %) та із дефіцитом/недостатністю вітаміну D (до 46,1 %).У обстежених дітей виявлені поліморфні варіанти гену VDBP, які можуть впливати рівень метаболітів вітаміну D у сироватці крові. Низькі концентрації 25(ОН)D мали переважно діти з генотипами СА rs 4588 та GT rs 7041, найвищі рівні 25(ОН)D – носії генотипів АА rs 4588 та ТТ rs 7041 гена VDBP.Застосування комбінації вітаміну D3 з пробіотичним штамом Lactobacillus reuteri DSM 17938 протягом 12 тижнів дозволило підвищити медіану концентрацій 25(OH)D у сироватці крові на 32,2 %, досягти його рівня понад 30 нг/мл у 75,0 % обстежених.Досягнення рівня 25(OH)D > 30 нг/мл сприяло зниженню частоти рекурентних респіраторних вірусних інфекцій (р=0,023), зменшувало шанси на виникнення повторних епізодів гострого обструктивного ларингіту (OR=9,00), а у разі розвитку захворювання – створювало умови для його більш легкого перебігу (OR=11,40).^UThe dissertation dedicated to the problems of improving efficiency of recurrent croup prevention. It was demonstrated that the rate of recurrent croup increases in children with a history of allergies, with dysfunction of the gastrointestinal tract and with a vitamin D insufficiency/deficiency. Insufficient levels of vitamin D were recorded in 46.1% of children with viral croup.Performed tests indicate the presence of polymorphic variants of the VDBP gene in children in Ukraine, which may affect the effectiveness of prevention of rickets by supplementation of vitamin D. Compared with the international database, the TT genotype rs 7041 and T allele rs 7041 were significantly more common in the examined children and the GG genotype rs 7041 and G allele rs 7041 were significantly less common. Optimal levels of 25(OH)D in serum, regardless of the dose of supplements, were demonstrated in all examined young children with genotype GG rs 7041 gene VDBP. Low concentrations of 25(OH)D were determined mainly in the examined children with genotypes CA rs 4588 and GT rs 7041 of the VDBP gene. The highest levels of 25(OH)D were recorded in children with genotypes AA rs 4588 and TT rs 7041 of the VDBP gene, which showed high absorption when taking vitamin D supplements at a dose of 500 IU and even excessive concentrations of 25(OH)D with long-term use supplements in a higher dose. For final conclusions on the potential impact of VDBP gene polymorphism on the effectiveness of prevention of vitamin D deficiency, it is necessary to conduct research on large cohorts of children and adults in Ukraine.The follow-up examinations showed that the use of a combination of vitamin D3 at a dose of 400 IU with the probiotic strain Lactobacillus reuteri DSM 17938 in children of the treatment group made it possible to reach a statistical difference in the median concentration of 25 (OH) D after 12 weeks of use compared to the same indicator at baseline: 37.4 ng/mL (30.2–52.3) versus 28.3 ng/mL (20.8–42.9), respectively (p = 0.000). The level of 25(OH)D in all these children exceeded 20 ng/mL; the concentration level of 25(OH)D exceeded 30 ng/mL in 75.0% of these.The use of vitamin D supplements in combination with Lactobacillus reuteri DSM 17938 had a positive effect on the functional activity of the gastrointestinal tract in young children and significantly reduced the frequency of parents' complaints of stool retention and anxiety during defecation in their children.There was a certain correlation between IgE levels, vitamin D status and intake of supplements containing L. reuteri DSM 17938.The use of 400 IU of vitamin D supplements in combination with L. reuteri for 12 weeks made it possible to reduce the median concentration of total IgE by almost half — from 64.1 IU/mL (9.2–120.0) to 31.9 IU/mL (6.4–143.6), but no significant difference was reached due to the substantial variability of data. The level of IgE increased significantly in 16.7 % of patients who had exacerbations of an allergic disease just before the follow-up examination. At the same time, 45.8 % of children had a clear positive dynamics. Given the small sample size, the comparison with the control group made it impossible to draw final conclusions. But children with high IgE levels responded more slowly to supplementation with pure vitamin D. Moreover, none of these patients reached the level of 25 (OH) D more than 30 ng/mL during the 12-week follow-up.When the concentration of 25(OH)D in serum increased to > 30 ng/mL, the frequency of recurrent ARIs decreased (p=0.023); the risks for recurrent episodes of viral croup decreased (OR=9.00), as well as the risks of more mild viral croup course (OR=11.40).