C-reactive protein, bone strength, and 9-year fracture risk: Data from the study of womens health across the nation (SWAN)

Journal of Bone and Mineral Research, 03/12/2013

The authors aimed to test the hypotheses that composite indices of femoral neck strength relative to load, which are inversely associated with fracture risk, would also be inversely associated with C–Reactive Protein (CRP), and would explain part of the association between CRP and fracture risk. They conclude that fracture risk increases with increasing CRP, only above the threshold of 3mg/L. Unlike bone mineral density (BMD), composite strength indices are inversely related to CRP levels, and partially explain the increased fracture risk associated with inflammation.

Methods

  • The authors analyzed data from a multi-site, multi-ethnic prospective cohort of 1872 community-dwelling women, pre- or early peri-menopausal at baseline.
  • Femoral neck composite strength indices in three failure modes were calculated using DXA-derived femoral neck width (FNW), femoral neck axis length (FNAL), femoral neck BMD and body size at baseline, as BMD*FNW/weight for compression strength, BMD*(FNW)2/(FNAL*weight) for bending strength, and BMD*FNW*FNAL/(height*weight) for impact strength.
  • Incident non-digital, non-craniofacial fractures were ascertained annually over median follow up of 9 years.

Results

  • In analyses adjusted for age, race/ethnicity, diabetes, menopause transition stage, body mass index, smoking, alcohol use, physical activity, medications, prior fracture and study site, CRP was associated inversely with each composite strength index (0.035 to 0.041SD decrement per doubling of CRP, all p<.001), but not associated with femoral neck or lumbar spine BMD.
  • During the follow-up, 194 women (10.4%) had fractures. In Cox proportional hazards analyses, fracture hazard increased linearly with log(CRP), only for CRP levels ? 3 mg/L.
  • Addition of femoral neck or lumbar spine BMD to the model did not attenuate the CRP-fracture association.
  • However, addition of any of the composite strength indices attenuated the CRP-fracture association and made it statistically non-significant.

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