Molecules from vitamin D group belong to organic, lipid-soluble substances classifed as secosteroids which are characterized by cleavage of the B ring of the core structure. Vitamin D receptors are localized on cells in many different types of tissues and organs which makes vitamin D has pleiotropic functions and influences on functioning of whole body and modifies course of different diseases. Calcitriol affects the biology of cells with two different pathways: genomic and non-genomic actions. Results of many surveys suggest the correlation between vitamin D concentration and risk of many different tumors. Vitamin D deficiency can play role in breast cancer, prostate cancer, colorectal cancer or malignant melanoma. Furthermore, vitamin D is crucial for calcium and phosphate homeostasis and it’s deficiency may cause musculoskeletal, cardiovascular and respiratory disorders.