It has been several years since the discovery of the pleiotropic effects of vitamin D, and there is still hot debate as to the role of vitamin D and attempts to standardise methods of determining 25(OH)D concentrations as well as supplementation with vitamin D. Many studies, both observational and randomised controlled trials, have revealed a whole range of opportunities of active vitamin D metabolite contribution to the treatment of common diseases. A relationship between high concentrations of vitamin D and a low risk of incidence of colorectal cancer, cardiovascular diseases, hypertension, ischaemic stroke, depression,metabolic syndrome and type 2 diabetes has been suggested for a long time, although recently published meta-analyses have created some doubts. There is no consensus regarding vitamin D supplementation and the optimum concentration of serum 25(OH)D. The Institute of Medicine’s 2011 report recommends achieving serum 25(OH)D concentration of 20 ng/mL as optimal, at a dosage of 600 IU of vitamin D per day. International recommendations suggest for individuals at risk a dosage of vitamin D of 2,000 IU per day. Polish experts advise that the optimal concentration of 25(OH)D should be greater than 30 ng/mL for adults
