Vitamin D - „the sunshine vitamin” is essential for the good functioning of the human body. The most important forms of the vitamin D are the vitamin D2 and the vitamin D3, both biologically inactived. Vitamin D can come from: diet or nutritiv suplimentts and skin. The activation of vitamin D is effect in two steps to the physiologically active 1,25-dihydroxyvitamin D [1,25(OH)2D]. The biological actions of Vitamin D involve regulation of gene expression at the transcriptional level and are mediated through binding to a Vitamin D Receptor (VDR). Vitamin D has multiple roles: hormonale/ nonhormonale, skeletale/nonscheletale, genomice/nongenomice. Interesting is inversely corelation between Vitamin D and total body fat (BMI) and correlation between Vitamin D and cognitive impairment, especially Alzheimer Disease or delirium during hospitalisation. The curent recomandations regarding the supplying with Vitamin D are different for regions of the globe, also differ depending on the baseline serum Vitamin D and on the desired effect. So, potential nonskeletal effects occur at levels >30ng/ml, above 50-75ng/ml, serum level who should become the target of the supplementation. The loading dose should be considered perioperatively for rapid effects. In conclusion, Vitamin D is more than just a vitamin. It is a substance with multiple roles in body’s economy, and in recent years there has been an interest in the relation be tween vitamin D deficiency and obesity or cognitive impairment. The majority of the data supports association, not causation, of low vitamin D levels. In other words, much of data does not clearly support the idea that vitamin D supplementation in a patient with low vitamin D levels reduces the risk of these diseases. But, the supplimentation is very easy and no harm might be done.