25-hydroxyvitamin D, parathyroid hormone, and functional recovery after hip fracture in elderly patients

There is increasing interest in the effects of vitamin D and parathyroid hormone (PTH) on extraskeletal tissues, including the muscle. These effects may explain impairment in functional ability found in vitamin D-deficient subjects. Our aim was to investigate the roles of vitamin D and PTH in affecting the ability to perform activities of daily living after hip fracture. We studied 456 of 521 hip-fracture patients admitted consecutively to a rehabilitation hospital. Functional outcome was assessed after acute inpatient rehabilitation by using the Barthel index score. The functional scores were significantly correlated with serum levels of 25-hydroxyvitamin D (rho = 0.190; P < 0.001) and PTH (rho = -0.164; P < 0.001) and the 25-hydroxyvitamin D/PTH ratio (rho = 0.261; P < 0.001). At multiple regression, 25-hydroxyvitamin D and PTH levels were independently associated with Barthel index scores. The correlation between the 25-hydroxyvitamin D/PTH ratio and Barthel index scores was significantly stronger than the one between 25-hydroxyvitamin D and Barthel index scores (difference between the two correlation coefficients = 0.071; 95% CI = 0.009-0.133; P = 0.011). The significant association between the 25-hydroxyvitamin D/PTH ratio and the Barthel index scores persisted after adjustment for 12 prognostic factors (P = 0.012). On the whole, the panel of prognostic factors we studied predicted 50.1% of the variance of the functional score. Data shows that PTH and 25-hydroxyvitamin D were significantly associated with the ability to function after hip fracture and suggest that the two hormones act through independent mechanisms. The 25-hydroxyvitamin D/PTH ratio significantly contributed to a predictive model of functional outcome.