Associations of elevated interleukin-6 and C-reactive protein levels with mortality in the elderly

PURPOSE: To investigate whether interleukin-6 and C-reactive protein levels predict all-cause and cause-specific mortality in a population-based sampl e of nondisabled older people. SUBJECTS AND METHODS: A sample of 1,293 healthy, nondisabled participants i n the Iowa 65+ Rural Health Study was followed prospectively for a mean of 4.6 years. Plasma interleukin-6 and C-reactive protein levels were measured in specimens obtained from 1987 to 1989. RESULTS: Higher interleukin-6 levels were associated with a twofold greater risk of death [relative risk (RR) for the highest quartile (greater than o r equal to 3.19 pg/mL) compared with the lowest quartile of 1.9 [95% confid ence interval, CI, 1.2 to 3.11]. Higher C-reactive protein levels (greater than or equal to 2.78 mg/L) were also associated with increased risk (RR = 1.6; CI, 1.0 to 2.6). Subjects with elevation of both interleukin-6 and C-r eactive protein levels were 2.6 times more likely (CI, 1.6 to 4.3) to die d uring follow-up than those with low levels of both measurements. Similar re sults were found for cardiovascular and noncardiovascular causes of death, as well as when subjects were stratified by sex, smoking status, and prior cardiovascular disease, and for both early (<2.3 years) and later follow-up . Results were independent of age, sex, body mass index, and history of smo king, diabetes, and cardiovascular disease, as well as known indicators of inflammation including fibrinogen and albumin levels and white blood cell c ount. CONCLUSIONS: Higher circulating levels of interleukin-6 and C-reactive prot ein were associated with mortality in this population-based sample of healt hy older persons. These measures may be useful for identification of high-r isk subgroups for anti-inflammatory interventions. (C) 1999 by Excerpta Med ica, Inc.