Associations between blood inflammatory markers and bone mineral density and strength in the femoral neck: findings from the MIDUS II study

Chronic and systematic inflammation have been related to increased risks of osteopenia and related fracture. However, studies concerning the association between low-grade inflammation and the bone mineral density (BMD) and strength of the femoral neck are still few and inconsistent. This study aimed to examine the relationships between blood inflammatory biomarkers and BMD and femoral neck strength in an adult-based cohort. We retrospectively analyzed a total of 767 participants included in the Midlife in the United States (MIDUS) study. The blood levels of inflammatory markers, including interleukin-6 (IL6), soluble IL-6 receptor, IL-8, IL-10, TNF-α and C-reactive protein (CRP), in these participants were measured, and their associations with the BMD and strength of the femoral neck were determined. We analyzed these 767 subjects with data concerning the BMD, bending strength index (BSI), compressive strength index (CSI), and impact strength index (ISI) in the femoral neck and inflammatory biomarkers. Importantly, our results suggest that strongly negative associations exist between the blood soluble IL6 receptor levels and the BMD (per SD change, Sβ = −0.15; P < 0.001), CSI (per SD change, Sβ = −0.07; P = 0.039), BSI (per SD change, Sβ = −0.07; P = 0.026), and ISI (per SD change, Sβ = −0.12; P < 0.001) in the femoral neck after adjusting for age, gender, smoked cigarettes regularly, number of years drinking, BMI and regular exercise. However, the inflammatory biomarkers, including blood IL-6 (per SD change, Sβ = 0.00; P = 0.893), IL-8 (per SD change, Sβ = −0.00; P = 0.950), IL-10 (per SD change, Sβ = −0.01; P = 0.854), TNF-α (per SD change, Sβ = 0.04; P = 0.260) and CRP (per SD change, Sβ = 0.05; P = 0.137), were not strongly associated with the BMD in the femoral neck under the same conditions. Similarly, there was no significant difference in the relationships between the inflammatory biomarkers (IL-6, IL-8, IL-10, TNF-α and CRP) and the CSI, BSI, and ISI in the femoral neck. Interestingly, in concomitant inflammation-related chronic diseases, only arthritis affected the soluble IL-6 receptor and the CIS (interaction P = 0.030) and SIS (interaction P = 0.050) in the femoral neck. In this cross-sectional analysis, we only observed that high blood levels of soluble IL-6 receptor were strongly associated with reduced BMD and bone strength in the femoral neck. The independent associations between the other inflammatory indicators, including IL-6, IL-8, IL-10, TNF-α and CRP, and the BMD and femoral neck strength in an adult-based cohort were not significant.