Appendicular Lean Mass Does Not Mediate the Significant Association Between Vitamin D Status and Functional Outcome in Hip-Fracture Women

Abstract

Di Monaco M, Castiglioni C, Vallero F, Di Monaco R, Tappero R. Appendicular lean mass does not mediate the significant association between vitamin D status and functional outcome in hip-fracture women. Objective To investigate whether muscle mass mediates the significant association between vitamin D status and functional recovery after hip fracture in women. Design Observational study. Setting Rehabilitation hospital in Italy. Participants We investigated white women (N=280) of 305 who were consecutively admitted to a rehabilitation hospital because of their first fracture of the hip. Interventions Not applicable. Main Outcome Measures To assess muscle mass, we measured appendicular lean mass (aLM) by dual-energy x-ray absorptiometry (DXA), 21.2±6.2 (mean ± SD) days after hip fracture occurrence in the 280 women. On the same day, we assessed serum levels of 25-hydroxyvitamin D and parathyroid hormone (PTH). Ability to function in activities of daily living was evaluated by the Barthel Index both before and after acute inpatient rehabilitation. Results After adjustment for 8 confounders, including age, cognitive impairment, pressure ulcers, neurologic impairment, infections, fracture type, Barthel Index score at admission to rehabilitation, and aLM/height 2 (aLM/ht 2), 25-hydroxyvitamin D levels were significantly associated both with Barthel Index scores after rehabilitation ( P=.003) and their changes during rehabilitation ( P=.008). Similar results were obtained when the 25-hydroxyvitamin D/PTH ratio was substituted for 25-hydroxyvitamin D levels. Conversely, aLM/ht 2 was not significantly correlated with Barthel Index scores and their changes during rehabilitation. Furthermore, we found no significant associations between either 25-hydroxyvitamin D levels or the 25-hydroxyvitamin D/PTH ratio and aLM/ht 2. Conclusions The significant association between 25-hydroxyvitamin D levels (and 25-hydroxyvitamin D/PTH ratio) and the ability to function in women with hip fractures was not mediated by aLM assessed by DXA.