Purpose: To investigate whether interleukin-6 and C-reactive protein levels predict all-cause and cause-specific mortality in a population-based sample of nondisabled older people.
Subjects and methods: A sample of 1,293 healthy, nondisabled participants in 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 (> or = 3.19 pg/mL) compared with the lowest quartile of 1.9 [95% confidence interval, CI, 1.2 to 3.1]). Higher C-reactive protein levels (> or = 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-reactive protein levels were 2.6 times more likely (CI, 1.6 to 4.3) to die during follow-up than those with low levels of both measurements. Similar results 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 smoking, diabetes, and cardiovascular disease, as well as known indicators of inflammation including fibrinogen and albumin levels and white blood cell count.
Conclusions: Higher circulating levels of interleukin-6 and C-reactive protein were associated with mortality in this population-based sample of healthy older persons. These measures may be useful for identification of high-risk subgroups for anti-inflammatory interventions.