Non-classical effects of Vitamin D (cholecalcipherol), related to its immunomodulating and antiproliferative activity have been known for 25 years. However, only recent years brought a better understanding of how these non-classical effects of cholecalcipherol influence patophysiology and prevention of many diseases. Review of scientific reports on vitamin D point out to three fundamental facts: 1) numerous population data prompt a reinterpretation of our understanding of physiological levels of Vitamin D and raise awareness of vitamin D deficiency becoming a global problem, 2) epidemiological data linked a vitamin D deficiency with a higher susceptibility to many diseases and increased mortality, 3) a much wider than previously considered existence of vitamin D receptors and an extra-renal, biochemical machinery capable of synthesizing an active form of vitamin D - 1,25-(OH)2-D3, (including lymphoid tissue, CNS, pancreas, parathyroid gland etc.). All this suggest that so called extra-skeletal function of vitamin D and its physiological impact may play an important role in human physiology, extending far beyond the skeletal and calcium homeostasis. In light of an accumulating evidence, appropriate supplementation of vitamin D (which seems to be higher than most of current recommendations) could lower or even prevent the prevalence of various clinical disorders.