Even in developed countries the prevalence of subjects with suboptimal vitamin D levels is high. The aim of this retrospective data analysis was to evaluate the prevalence of severe and moderate vitamin D deficiencies (defined as vitamin D levels<15 ng/ml and 15-30 ng/ml, respectively) among patients evaluated at Semmelweis University during a period between April, 2009 and March, 2010. Methods and results: The average vitamin D level of 5808 subjects (3936 women and 1872 men) was 25.5 +/- 10.9 ng/ml. The prevalence of moderate and severe vitamin D deficiency in whole population was 72% and 12%, respectively. Higher than normal vitamin D levels were measured in 0.8% of subjects. Female gender, older age and winter season were independent risk factors for vitamin D deficiency. Vitamin D levels were measured repeatedly in 1307 subjects. Interestingly, vitamin D levels measured later were lower compared to those measured at the first time (27.07+/-13.2 vs. 25.9+/-9.11 ng/ml, p<0.001). The prevalence of severe and moderate vitamin D deficiency was 8.1 and 71.5 per cent when vitamin D levels were measured at the second time. Of the 110 patients with severe vitamin D deficiency measured repeatedly only 11 patients (10%) presented with normal vitamin D levels at the second time. Conclusions: These data indicate that severe and moderate vitamin D deficiencies are common in patients evaluated at Semmelweis University. Repeated measurements of vitamin D levels raise the notion that the efficacy of supplementation used for correction of vitamin D levels is not optimal
