Associations between plasma insulin-like growth factor-I and the markers of inflammation interleukin 6, C-reactive protein and YKL-40 in an elderly background population

The objective of the present study was to test the hypothesis that circulating levels of insulin-like growth factor-I (IGF-I) are inversely associated with inflammatory processes in an elderly background population. We conducted a population-based study comprising 629 individuals, aged 50-89 years. Associations between plasma IGF-I versus interleukin 6 (IL-6) and the acute phase proteins high sensitive C-reactive protein (hsCRP) and YKL-40 were evaluated by linear regression analyses. Subsequently, the population was dichotomised at a CRP level of 3.0 mg/L and the associations were re-evaluated in the two subgroups. Adjusted for confounding variables, plasma IGF-I was inversely related to IL-6, hsCRP and YKL-40 (all P < 0.001). The strongest association was found for YKL-40 with a 34% reduction in YKL-40 per twofold increase in IGF-I. A significant inverse association between IGF-I and all markers of inflammation persisted in individuals with hsCRP below 3.0 mg/L whereas only YKL-40 was significantly associated with IGF-I in individuals with hsCRP above 3.0 mg/L. The data support the hypothesis of an inverse association between GH/IGF-I signalling and inflammation, and suggest that the relationship between the IGF-I and inflammation might be more predominant in healthy individuals with a low inflammatory activity.