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Keywords:

  • aging;
  • cognition;
  • inflammation;
  • interleukin-6

Abstract

Background

Inflammation is involved in the pathogenesis of cardiovascular disease and cognitive decline. Interleukin-6 (IL-6) has a role in cardiovascular disease, but the association of IL-6 concentration and the functional IL-6 -174 polymorphism with cognitive decline has not been demonstrated unequivocally. The objective of this study was to investigate the associations between both high concentration of IL-6 and the -174 promoter polymorphism, and increased cognitive decline in old age.

Methods

Over 5000 participants of the Prospective Study of Pravastatin in the Elderly at Risk (PROSPER) with a mean age of 75 years and a history of cardiovascular disease or its risk factors were included in this study. We determined baseline concentrations of IL-6 and genotype of the IL-6 -174 polymorphism, of which the C allele was previously shown to be associated with higher circulating concentrations of IL-6. A cognitive test battery was administered at baseline and repeatedly during follow-up (mean 39 months).

Results

In the cross-sectional analysis of 5653 participants, higher IL-6 concentration was associated with worse executive cognitive function (< 0.001), independent of cardiovascular disease status and risk factors. No association was found between IL-6 concentration and memory function (> 0.14). In the prospective analysis, higher IL-6 concentration was associated with an increased rate of cognitive decline in both executive function (= 0.002) and memory function (= 0.002), again independent of cardiovascular disease status and risk factors. Although not associated with IL-6 concentrations, the IL-6 -174 CC genotype was associated with worse performance on the Stroop test (= 0.045).

Conclusions

Higher circulating levels of IL-6 were associated with worse cognitive function and steeper cognitive decline and provide preliminary genetic evidence for a potential causal association. The findings support the importance of the need for further investigation of the IL-6 pathway in cognitive decline.