Association of Serum Vitamin D Levels With Inflammatory Response Following Hip Fracture: The Baltimore Hip Studies

BACKGROUND: Vitamin D, known for its role in calcium homeostasis, may also regulate immune function. Whether vitamin D deficiency at the time of hip fracture is associated with the inflammatory response postfracture is not known. METHODS: In a cohort from the Baltimore Hip Studies, women aged >or= 65 years were evaluated at baseline and 2, 6, and 12 months after hip fracture repair. Serum at baseline was analyzed for 25-hydroxyvitamin D [25(OH)D], and serum from all time points was analyzed for interleukin-6 (IL-6). Participants were divided into two groups based on their baseline 25(OH)D levels. Vitamin D deficiency was defined as a 25(OH)D level of <or= 15 ng/mL (<37.5 nmol/L). We examined IL-6 level as a function of vitamin D status using generalized estimating equations, adjusting for covariates. RESULTS: Women deficient in vitamin D at baseline had higher IL-6 levels in the year postfracture (p=.02). On average, participants with low 25(OH)D levels had adjusted serum IL-6 levels that were 6.0 pg/mL (95% confidence interval [CI]: -6.7, 18.7 pg/mL), 11.9 pg/mL (95% CI: 3.5, 20.4), 13.1 pg/mL (95% CI: 4.6, 21.6), and 13.4 pg/mL (95% CI: 2.3, 24.5) higher at baseline, 2, 6, and 12 months after hip fracture, respectively. CONCLUSIONS: Women with vitamin D deficiency at the time of hip fracture had higher serum IL-6 levels in the year after hip fracture. Whether the proinflammatory state of vitamin D deficiency explains the association of this deficiency with adverse outcomes in older adults warrants further study.