The relationship between interleukin-6 levels and physical performance in mobility-limited older adults with chronic low-grade inflammation: The ENRGISE Pilot study

Abstract

Previous studies have found an inverse relation between serum concentrations of interleukin (IL)-6 and physical performance in seniors, however this was limited to higher functioning older adults with low to moderate levels of inflammation. We explored the consistency of this association in a cohort of mobility limited older adults with chronic low-grade inflammation. This study included 289 participants (≥ 70 years old) with IL-6 level between 2.5 and 30 pg/mL and a walking speed < 1.0 m/sec from the ENRGISE Pilot study. Physical performance was assessed using the short physical performance battery (SPPB), usual gait speed over 400 m, grip strength, and knee extensor and flexor strength measured by isokinetic dynamometry at 60 and 180°/sec. There was a significant inverse correlation between log IL-6 and knee extensor strength at 60°/sec (r= -0.20, p = 0.002), at 180°/sec (r = -0.14, p = 0.037), and knee flexor strength at 60°/sec (r = -0.15, p = 0.021). After adjustment for potential confounders, the values of knee extensor strength at 60°/sec showed a trend toward a progressive reduction across IL-6 tertiles as IL-6 levels increased (p = 0.024). No significant association was found between IL-6 and other objectively measured physical performance. The findings were generally of smaller magnitude and less consistent than previously reported, which suggests that the associations are attenuated in those with both elevated inflammation and mobility limitations. These results have implications for planning and interpreting future intervention studies in older adults with low-grade inflammation and mobility limitations.

Keywords: Chronic low-grade inflammation; Interleukin-6; Knee muscle strength; Physical performance.

Figure 1.

Adjusted knee extensor strength at 60°/sec across IL-6 tertiles from ANCOVA model adjusted for age, gender, race, BMI, former smoker status, ≥ 2 comorbidities, use of renin angiotensin system inhibitors, use of lipid-lowering drugs, and use of anti-inflammatory medications. The box indicates the 25^th to 75^th percentile; the line inside the box, the median; the symbol inside the box, the mean; the bars, the largest and smallest non-outlier values; the symbols outside the bars, the outliers.