Vitamin D plays a significant role in regulating the metabolism of the bone tisuse and has been associated with several diseases. Rickets and osteomalacia are classical vitamin D deficiency diseases. There is considerable discussion about the serum concentrations of 25(OH)D (50 vs. 75 nmol/l) associated with optimaal overall health while there has not been consensus regarding adequate cut-off points. At present, based on the results of several studies, the Board of the Institute of Medicine has concluded that a level of no less than 50 nmol/l (20 ng/ml) is sufficient. Considering the geographical location (exposure to sunlight is limited) of Estonia and the indoor lifestyle, it is recommended to consider vitamin D supplementation. Vitamin D is a fat-soluble vitamin which is present in fish-oils, eggs, fortified dairy products, f lesh of fatty fishes and butter.