Introduction and objective:
Vitamin D3 is one of the most essential endogenous compounds synthesized in the human body. Originally, its deficiency was associated with the occu-rrence of rickets in children. However, a number of studies carried out over the last decades indicated that vitamin D3 is much more important than previously thought. The aim of this study was to analyze the available scientific literature on vitamin D3 and its effects on human health.

Review methods:
The following combinations of key words were used to search the Pubmed database: [vitamin D] + [synthesis, metabolism, receptor, epidemiology, deficiency, SARS-CoV-2]. After applying exclusion criteria, 67 articles were selected for review.

Abbreviated description of the state of knowledge:
About 90% of vitamin D3 is produced in the skin as a result of exposure to UVB radiation. The remaining portion is supplied from food or dietary supplements. It is postulated that vitamin D3 deficiency is one of the most pressing health problems today. Literature data indicate that vitamin D3 deficiency severely disrupts the body’s homeostasis and increases the risk of certain cancers, cardiovascular diseases, and type 2 diabetes. Since the 2019 outbreak of the SARS-CoV-2 coronavirus pan-demic, clinical studies have been initiated on the effects of vitamin D3 on susceptibility to infection and disease course. It has been found to have beneficial effects in preventing infection and mitigating the effects of COVID-19.

With the progress of medicine it has been under-stood how important vitamin D3 is for the proper functioning of the body and what health consequences its deficiency entails. Therefore, from the point of view of public health it is important to make the general public aware of the im-portance of this vitamin for health and the advantages of its regular intake.

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