Association between Serum Interleukin-6 Concentrations and Mortality in Older Adults: The Rancho Bernardo Study

Background: Interleukin-6 (IL-6) may have a protective role in acute liver disease but a detrimental effect in chronic liver disease. It is unknown whether IL-6 is associated with risk of liver-related mortality in humans. Aims: To determine if IL-6 is associated with an increased risk of all-cause, cardiovascular disease (CVD), cancer, and liver-related mortality. Methods: A prospective cohort study included 1843 participants who attended a research visit in 1984-87. Multiple covariates were ascertained including serum IL-6. Multivariable-adjusted Cox proportional hazards regression analyses were used to examine the association between serum IL-6 as a continuous (log transformed) variable with all-cause, CVD, cancer, and liver-related mortality. Patients with prevalent CVD, cancer and liver disease were excluded for cause-specific mortality. Results: The mean (+/- standard deviation) age and body-mass-index (BMI) of participants was 68 (+/- 10.6) years and 25 (+/- 3.7) Kg/m(2), respectively. During the 25,802 person-years of follow-up, the cumulative all-cause, CVD, cancer, and liver-related mortality were 53.1% (N = 978), 25.5%, 11.3%, and 1.3%, respectively. The median (+/- IQR) length of follow-up was 15.3 +/- 10.6 years. In multivariable analyses, adjusted for age, sex, alcohol, BMI, diabetes, hypertension, total cholesterol, HDL, and smoking, one-SD increment in log-transformed serum IL-6 was associated with increased risk of all-cause, CVD, cancer, and liver-related mortality, with hazard ratios of 1.48 (95% CI, 1.33-1.64), 1.38 (95% CI, 1.16-1.65), 1.35 (95% CI, 1.02-1.79), and 1.88 (95% CI, 0.97-3.67), respectively. CRP adjustment attenuated the effects but the association between IL-6 and all-cause and CVD mortality remained statistically significant, independent of CRP levels. Conclusions: In community-dwelling older adults, serum IL-6 is associated with all-cause, CVD, cancer, and liver-related mortality.