Beyond Inflammaging: The Impact of Immune System Aging on Age-Related Muscle Decline, Results From the InCHIANTI Study

Aging is characterized by chronic low-level inflammation and is associated with geriatric syndromes such as sarcopenia and frailty. Our aim was to evaluate the longitudinal variation of muscle area, muscle quality, and muscle strength, relative to the variation of leukocyte-derived markers, and to assess the presence of a pathway of associations among derived leukocyte ratios, and the components of muscle health. The InCHIANTI is a longitudinal cohort study of aging that began in 1998 with follow-up visits every 3 years. Out of the 1 453 participants enrolled at baseline, this study includes 1 179 participants with complete data. Muscle strength was assessed by hand grip strength test, whereas muscle density and fat area were considered as indirect markers of muscle quality, derived from peripheral quantitative computed tomography of the calf. Muscle area was associated with neutrophil-to-lymphocyte ratio (NL-ratio), age, gender, comorbidities, and body mass index (BMI). Muscle density variation over time was inversely associated with age, comorbidities, and BMI, while being positively associated with monocyte-to-lymphocyte ratio (ML-ratio) and male gender. Fat area was inversely associated with age, interleukine-6 (IL-6), male gender, and NL-ratio, while being positively associated with ML-ratio, comorbidities, and BMI. Handgrip strength decreased with age, IL-6 levels, comorbidities, and NL-ratio, but increased with ML-ratio, being male, and having a higher BMI. In a path-analysis model, ML-ratio positively correlates with muscle mass, density, and strength, while NL-ratio only correlates inversely with muscle mass and density. NL-ratio and ML-ratio are associated with aging and may be implicated in age-related mechanisms that affect body composition and muscle strength. These ratios may represent a link between aging of the immune system and decline of muscle health with aging. However, further studies are needed to identify their usefulness for early detection of sarcopenia, myosteatosis, and frailty in the older adult.