Conclusion:
The overall prevalence of vitamin D deficiency in hospital admitted subjects is similar to those in hospital-derived studies from national Turkish and European populations. In this cohort, over half of the subjects admitted to the general hospitals in Turkey had vitamin D deficiency requiring vitamin D supplementation. Although this retrospective study was not able to exclude vitamin D-related diseases and vitamin D-treated patients, the highest prevalence of hypervitaminosis D is observed in the elderly population that may indicate overtreatment vitamin D supplementation in the tertiary care hospitals in Turkey. Further prospective studies are needed to guide appropriate vitamin D supplementation for subgroups and to prevent overtreatment.