Skeletal Muscle Function Deficit Longitudinal Associations With Inflammation and Caloric Intake in Elderly. The...

The Skeletal Muscle Function Deficit (SMFD) score integrates muscle mass, strength, power and quality into a single construct that evaluates the multidimensional status of muscle health. The aim of the study is to investigate the longitudinal associations of systemic inflammation and caloric intake with SMFD-score trajectories in older adults from the InCHIANTI study.

Data were obtained from the InCHIANTI population-based longitudinal cohort. A total of 1035 community-dwelling older adults (mean age 74.97 ± 7.39 years; 44.25% men) contributed 3196 repeated observations across four study waves. SMFD-score (range 0-20) was derived from sex-specific quintiles of lower-limb muscle mass, muscle density, grip strength and lower-limb power; participants unable to perform a test received a score of 0 for that component. Interleukin-6 (IL-6) and caloric intake (kcal/day) were assessed at all study waves. Longitudinal associations between time-varying IL-6 tertiles, caloric intake tertiles and SMFD-score trajectories were evaluated using linear mixed-effects models adjusted for baseline age and sex and time-varying multimorbidity and body mass index.

Across follow-up, SMFD-score declined significantly from 9.60 ± 4.20 at baseline to 7.07 ± 4.00 at the last wave (p < 0.001), whereas IL-6 increased from 3.65 ± 2.50 pg/mL to 4.39 ± 3.10 pg/mL (p < 0.001). Mean caloric intake showed a non-significant upward trend (1912.83 ± 562.37 to 1976.00 ± 580.54 kcal/day; p = 0.07). In mixed-effects models, higher IL-6 levels were associated with accelerated SMFD decline over time (IL-6 tertile × time interaction β = -0.31 ± 0.02; p < 0.001). Higher caloric intake was associated with higher SMFD-score and a slower functional decline (caloric intake tertile main effect β = 1.19 ± 0.16; p < 0.001; caloric intake tertile × time interaction β = 0.24 ± 0.03; p < 0.001). In the model including the combined IL-6 × caloric intake × time interaction was statistically significant (β = 0.14 ± 0.04; p < 0.001), indicating that higher caloric intake partially attenuated the negative longitudinal association between IL-6 and SMFD-score.

SMFD-score captures longitudinal muscle function decline during aging and reflects the opposing influences of inflammation and caloric intake. These findings support the SMFD-score as a clinically relevant construct for identifying potentially modifiable determinants of muscle health and functional decline in older adults.