Serum IL-6 level and the development of disability in older persons

BACKGROUND: The serum concentration of interleukin 6 (IL-6), a cytokine tha t plays a central role in inflammation, increases with age. Because inflamm ation is a component of many age-associated chronic diseases, which often c ause disability, high circulating levels of IL-6 may contribute to function al decline in old age. We tested the hypothesis that high levels of IL-6 pr edict future disability in older persons who are not disabled. METHODS: Participants at the sixth annual follow-up of the Iowa site of the Established Populations for Epidemiologic Studies of the Elderly aged 71 y ears or older were considered eligible for this study if they had no disabi lity in regard to mobility or in selected activities of daily living (ADL), and they were re-interviewed 4 years later. Incident cases of mobility-dis ability and of ADL-disability were identified based on responses at the fol low-up interview. Measures of IL-6 were obtained from specimens collected a t baseline from the 283 participants who developed any disability and from 350 participants selected randomly (46.9%) from those who continued to be n on-disabled. FINDINGS: Participants in the highest IL-6 tertile were 1.76 (95% CI, 1.17- 2.64) times more likely to develop at least mobility-disability and 1.62 (9 5% CI, 1.02-2.60) times more likely to develop mobility plus ADL-disability compared with to the lowest IL-6 tertile. The strength of this association was almost unchanged after adjusting for multiple confounders. The increas ed risk of mobility-disability over the full spectrum of IL-6 concentration was nonlinear, with the risk rising rapidly beyond plasma levels of 2.5 pg /mL. INTERPRETATION: Higher circulating levels of IL-6 predict disability onset in older persons. This may be attributable to a direct effect of IL-6 on mu scle atrophy and/or to the pathophysiologic role played by IL-6 in specific diseases.