Vitamin D supplementation in patients with urolithiasis and hypercalciuria is considered to be unsafe. We analyzed the impact of vitamin D supplementation on selected health status parameters in children with idiopathic hypercalciuria. The study included 36 children with urolithiasis resulting from excessive calcium excretion. The level of calcium and 25(OH)D (hydroxylated vitamin D - calcidiol) in serum, urinary calcium excretion and the presence of stones in urinary tract were assessed prospectively. Blood and urine samples were collected at the time when the patient was qualified for the study and every three months up to 24 month of vitamin D intake at a dose of 400 or 800 IU/day. At time zero and at 12, and 24 months of vitamin D supplementation, densitometry was performed. Supplementation with vitamin D caused a statistically significant increase in the concentration of 25(OH)D in serum. There were no significant changes in calcium concentration in serum, excretion of calcium in urine but also in bone density. There was no significant increase in the risk of formation or development of stones in the urinary tract. Supplementation with vitamin D (400–800 IU/day) in children with idiopathic hypercalciuria significantly increases 25(OH)D concentration, does not affect calciuria, but also does not improve bone density.

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Vitamin D is a fat-soluble steroid hormone. Its main role is to regulate calcium and phosphate levels, which are strictly associated with ossification and bone homeostasis. However, due to the presence of a nuclear vitamin D receptor (VDR) in the majority of cells of the human body, vitamin D also displays multiple effects beyond the bones. Calcitriol (1,25(OH)2D) not only affects cell growth and differentiation, but also stimulates the immune system by, for example, modulating the production of IL-4 and IL-5 anti-inflammatory cytokines. High numbers of VDRs have been found on macrophages, dendritic cells and lymphocytes, among other cells, which can be considered a very strong argument for the participation of vitamin D in autoimmune and anti-inflammatory processes. In recent months we have been witnessing the development of the COVID-19 pandemic. One of the most dangerous consequences of SARS-CoV-2 infection is acute respiratory distress syndrome caused by the activation of lung macrophages and the so-called cytokine storm. A recent study on COVID-19 patients suggests that vitamin D activates the innate immune response and suppresses the acquired immune response; the resultant decreased cytokine expression can reduce the severity of inflammation associated with COVID-19. Among older children and adults, vitamin D deficiency is widespread and observed worldwide, including in the Polish population. Based on numerous studies, normal serum vitamin D levels were established. Vitamin D concentration below 20 ng/mL is considered deficient and a level between 20 and 30 ng/mL is regarded as suboptimal. An optimal vitamin D concentration is 30–50 ng/mL.