Elderly patients with hip fracture and subnormal renal function have inadequate response to vitamin D supplementation

Introduction: All Danish citizens aged >70 years are recommended to take vitamin D supplements. We hypothesized that renal insufficiency may impair the activation and effect of vitamin D supplements. We aimed to investigate the association between use of vitamin D supplements, and levels of 25-hydroxy-vitamin D and parathyroid hormone (PTH) in elderly patients according to estimated glomerular filtration rate (eGFR). Methods: The study was a sub-analysis of 164 patients with 25-hydroxy-vitamin D levels measured in a crosssectional study of 200 consecutive patients aged >= 65 years admitted to hospital with hip fracture. Results: Vitamin D supplement-users (n = 68) had significantly higher 25-hydroxy-vitamin D levels regardless of eGFR < or>60 ml/min. In patients with eGFR>60 ml/min (n = 103), median PTH levels were significantly lower in vitamin D supplement-users compared to non-users (4.8 [4.2-6.7] vs 6.25 [4.9-8.3] pmol/l, P = 0.039), while there was no difference in patients with eGFR<60 ml/min (9.5 [5.4-16.7] vs 9.8 [5.9-16.9] pmol/l, P = 0.66 (n = 61)). Conclusions: Use of vitamin D supplements was associated with increased levels of 25-hydroxy-vitamin D, but only associated with decreased levels of PTH in patients with eGFR>60 ml/min. Thus, renal function may be essential to gain effect of vitamin D supplements, and 25-hydroxy-vitamin D levels may not reflect active Vitamin D status in elderly vitamin D supplement-users with hip fracture and decreased renal function. In addition to current guidelines for prescription of vitamin D supplements, it may be considered to monitor PTH or active vitamin D in elderly patients with eGFR<60 ml/min and adjust dose accordingly.