Introduction Vitamin D deficiency consequences may go beyond altered calcium homeostasis and musculoskeletal disease. Medical inpatients are often vitamin D-deficient, but little information is available about the relation of vitamin D status with extra-skeletal disorders in this population. Methods We analysed the relationship between the concentrations of 25-hydroxyvitamin D [25(OH)D], the marker of vitamin D status, and the conditions most commonly causing admission in 115 consecutive medical inpatients. Results Sixty-five subjects (56.5%) had severe vitamin D deficiency [25(OH)D <8 ng/ml]. Age (β = -0.35, p = 0.01) and hepatic disease (β = -0.21, p = 0.02) were significant correlates of 25(OH)D levels. Compared with patients with ≥ 8 ng/ml 25(OH)D, those with <8 ng/ml 25(OH)D had significantly higher parathyroid hormone (PTH) concentrations [123 (92.7-208.2) ng/l vs. 88 (68.5-129.5) ng/l, p <0.001], were significantly more likely to have arterial hypertension (OR 2.76, 95% CI 1.16-6.58), heart failure (HF) (OR 2.49, 95% CI 1.14-5.47), cerebrovascular disease (OR 3.23, 95% CI 1.41-7.39), and infections (OR 2.44, 95% CI 1.02-5.87), and stayed in hospital significantly longer (10 days vs. 7.5 days, p = 0.01). Only the probability of having an infection remained significantly higher in cases with severe vitamin D deficiency after adjustment for age (OR 2.41, 95% CI 1.03-5.68) and persisted after further correcting for presence of hepatic disease and PTH values (OR 2.66, 95% CI 1.03-6.88). A significant association between PTH and HF (OR 2.32, 95% CI 1.05-5.09) and length of hospitalisation (β = 0.22, p = 0.04) emerged in the fully adjusted regression models. Conclusions Severe vitamin D deficiency is associated with commonly presenting extra-skeletal diseases in medical inpatients. With the exception of infections, this association is mainly driven by age. Additional studies are needed to determine whether vitamin D testing on admission may help stratifying specific categories of patients by clinical severity.
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