Background: Patients with dementia have higher levels of peripheral inflammatory markers. We investigated whether midlife levels of interleukin-6 (IL-6) and C-reactive protein (CRP) predicted concurrently evaluated intelligence and eventual cognitive impairment in order to determine their causal function.
Method: In the cohort study, the mean values of IL-6 and CRP were measured in 100 individuals taking irregular supplements of vitamins (27.8% of whom were women) between Oct 2019 and May 2020 and June 2020 and Oct 2020. These values were then divided into tertiles to examine a 1-year decline in the mean (mean = 1, SD = 2) standardised scores of verbal fluency, memory, and reasoning. Logistic regression was used to model declines greater than 2 points. For the baseline age, sex, and education, as well as for subsequent analyses, adjustments were made to the analyses.
Result: In cross-sectional research, participants with high IL-6 levels had poorer reasoning scores (0.08 SD; 95% [CI] 20.13, 20.02). In a retrospective study, participants with high IL-6 had a 1-year reduction in reasoning that was larger (p-value = 0.02) than that of those with low IL-6 (20.28; 90% CI 20.30, 20.26) (20.34; 90% CI 20.36, 20.32). In none of the tests, CRP was connected to deterioration.
Conclusion: The overall cross-sectional and long term impacts across the 1-year observation time approximated to an age effect of 2.5 months; elevated IL-6 but not CRP in midlife indicates cognitive deterioration.
Key words: Interleukin-6, C-reactive protein, Dementia, cognitive impairment
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