Long-term variability of inflammatory markers and associated factors in a population-based cohort

Objectives: To investigate long-term variability in serum high-sensitivity C-reactive protein (CRP) and interleukin-6 (IL-6) and to determine associated risk factors for high-risk inflammatory profiles.

Design: Prospective population-based cohort study.

Participants: Participants (N = 1,443) of the Epidemiology of Hearing Loss Study and the Beaver Dam Eye Study, two population-based prospective studies of aging in the same cohort.

Measurements: In participants aged 43 to 79 at the initial examination (1988-1990), serum high-sensitivity CRP was measured from three time-points (1988-1990, 1998-2000, 2009-2010), and serum IL-6 was measured from two (1998-2000, 2009-2010).

Results: When IL-6 levels were categorized into tertiles, 50.8% of participants were in the same group 10 years later (weighted kappa (κ) = 0.34). When CRP was categorized into three risk groups, 53.4% of participants were in the same group 10 years later (κ = 0.36), and 32.4% were in the same group at all three examinations (κ = 0.27). IL-6 increased from a geometric mean of 1.54 pg/L to 1.78 pg/L over 10 years, whereas CRP increased from a geometric mean of 1.67 mg/L to 2.25 mg/L over 10 years and then decreased to 1.93 mg/L over the next 10 years. These 10-year decreases in CRP were not observed in those not reporting statin use. Factors associated with long-term higher levels of IL-6 and CRP were older age (IL-6), obesity, smoking, lower physical activity (IL-6), lower high-density lipoprotein cholesterol (IL-6), and a history of statin (non)use (CRP).

Conclusion: Inflammatory marker levels tracked over the long term into older age with within-person increases were observed. Several potentially modifiable risk factors were associated with long-term higher levels of inflammatory markers.