The vitamin D endocrine system modulates an arsenal of important biological functions in more than 30 different tissues in short- and long-term perspectives. Two membrane receptors and one nuclear receptor are suggested to be involved in the vitamin D signaling system, but the function and physiological relevance of the receptors are debated. The complexity of the vitamin D endocrine system makes it necessary to combine experimental data with in silico simulations to get a holistic view of vitamin D-dependent regulation of tissue and cell physiology. This review focus on binding characteristics for the three putative vitamin D receptors and proposes a future systems biology approach including mathematical modeling that will be helpful together with experimental methods in depicting antitumoral and other biological effects promoted by the vitamin D endocrine system.