Objectives - the associations between vitamin D concentrations and respiratory diseases have been assessed in a large and rapidly expanding literature. Observational studies and numerous randomized trials. Data sources: - Medline, Embase, the Cochrane Central Register of Controlled Trials, Web of Science, ClinicalTrials.gov, and the International Standard Randomized Controlled Trials Number registry from 2011 to 2021. Vitamin D plays an essential role in maintaining bone health through regulating calcium concentrations in the body. The development of vitamin D deficiency is associated with deteriorating bone health and in severe cases, hypocalcemia, rickets, and osteomalacia in children and adults. Those at greatest risk of vitamin D deficiency include patients with chronic illnesses (e.g., chronic kidney disease, cystic fibrosis, asthma, and sickle cell disease), dark-pigmented skin, poor nutrition, and infants who are exclusively breastfed. The primary source of vitamin D is sunlight exposure with nutritional intake. However, the composite literature is often confusing and has led to heated debates about the optimal concentrations of vitamin D and related guidelines for supplementation. According to the last period of research, the impact of vitamin D is actively discussing the correct functioning of the immune system. It is established that it participates in the formation of the innate and adaptive immune response. In last years appeared data from controlled trials where there are confirmed D hypovitaminosis correlations with infections. The systemic review of the randomized controlled trials and meta analysis showed the effectiveness of vitamin D supplementation for reducing morbidity with respiratory diseases. In literary sources, the impact of Vitamin D is considered to influence the duration and severity of pneumonia. The authors note that in the cases of severe and complicated pneumonia, the concentrations of vitamin D was significantly lower than in control cases. It has been proposed that the activation of the vitamin D receptor (VDR) signaling pathway may generate beneficial effects in ARDS caused by SARS-CoV-2 with decreasing the cytokine/chemokine storm, regulating the renin‑angiotensin system, modulating neutrophil activity. The systemic review of the randomized controlled trials and meta analysis showed the effectiveness of vitamin D supplementation for reducing morbidity with respiratory diseases. But most of researchers have concluded that data remain uncertain and requires confirmation in farther well designed randomized controlled trials.