Association between combined interleukin-6 and C-reactive protein levels and pulmonary function in older women: results from the Women's Health and Aging Studies I and II.

OBJECTIVES: To determine whether combined higher interleukin-6 (IL-6) and C-reactive protein (CRP) levels are associated with lower pulmonary function levels in older women, accounting for chronic inflammatory diseases, physical function, and other factors associated with inflammation. DESIGN: Cross-sectional study using data from two prospective cohorts. SETTING: Baltimore, Maryland. PARTICIPANTS: Eight hundred forty disabled and 332 higher-functioning community-dwelling women aged 65 and older from the Women's Health and Aging Studies (WHAS) I and II, respectively. MEASUREMENTS: IL-6 and CRP, combined according to their tertile concentrations, and pulmonary function measures, assessed according to forced expiratory volume in 1 second (FEV₁) and forced vital capacity (FVC). RESULTS: In WHAS I and II, similar dose-response trends were observed between combined higher IL-6 and CRP levels and lower pulmonary function levels. In WHAS I (disabled women), the combined highest IL-6 and CRP levels were associated with the lowest levels of FEV₁ (mean 137.0 mL, 95% confidence interval (CI)=128.4-145.7 mL) and FVC (mean 191.7 mL, 95% CI=180.4-202.9 mL). Similarly, in WHAS II (higher-functioning women), the combined highest IL-6 and CRP levels were associated with the lowest levels of FEV₁ (mean 1,543 mL, [corrected] 95% CI=146.3-170.4 mL) and FVC (mean 224.2 mL, 95% CI=209.9-238.5 mL). CONCLUSION: Combined elevations in IL-6 and CRP were associated with the lowest pulmonary function levels in older women. These findings suggest that high IL-6 and CRP levels may be an indication of prevalent impaired pulmonary function. Future studies should determine whether measurement of IL-6 and CRP could enhance current methods of monitoring respiratory diseases beyond that provided by pulmonary function measures.