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.
Miller
Ram R
RR
Division of Gerontology , Department of Epidemiology and Preventive Medicine, University of Maryland School of Medicine, Baltimore, MD 21201, USA. rrmiller@epi.umaryland.edu
Hicks
Gregory E
GE
Shardell
Michelle D
MD
Cappola
Anne R
AR
Hawkes
William G
WG
Yu-Yahiro
Janet A
JA
Keegan
Achsah
A
Magaziner
Jay
J
D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D005260:Female; D006620:Hip Fractures / Q000097:blood*; D006801:Humans; D007249:Inflammation / Q000209:etiology*; D015850:Interleukin-6 / Q000097:blood; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood*
D015850:Interleukin-6; D014807:Vitamin D; C104450:25-hydroxyvitamin D