To Örebro University

While age-related elevations in systemic inflammation may contribute to the accelerated loss of skeletal muscle mass, previous findings have been based on a limited number of biomarkers. Moreover, whether links between inflammation and muscle mass are independent of protein intake and habitual physical activity (PA) remain unknown.

PURPOSE: The aim of the study was to explore links between skeletal muscle mass and inflammatory biomarkers in older women with different metabolic risk status, while accounting for adherence to guidelines on protein intake and PA.

METHODS: Skeletal muscle mass index (SMI) was assessed in 112 women (67±1.5 years) by bioelectrical impedance together with the equation of Janssen et al. (2002) to obtain muscle mass expressed in relation to body weight. Fasting blood samples were obtained following standardized protocols. Acute-phase proteins C-reactive protein (CRP) and fibrinogen were determined, together with the following inflammatory biomarkers: Adiponectin, Oncostatin-M (OSM), Leukemia inhibitory factor-receptor (LIF-R), Interleukin-6 (IL-6), IL-8, IL-12, and IL-18. Protein intake and PA were determined during 6 days by food record and accelerometry, respectively. Classification of metabolic risk status was based on the metabolic syndrome. Multivariate regression models were used to explore links between SMI and inflammatory biomarkers while adjusting for adherence to PA and protein intake guidelines and metabolic risk status.

RESULTS: Variations in SMI were inversely linked to levels of CRP (β-coefficient: -0.47; p< 0.05) and OSM (-0.20 p< 0.05), where the OSM link was attenuated after further adjustment for PA. In contrast, positive links between SMI and adiponectin (0.19 p< 0.05) and LIF-R (0.24 p< 0.05) were observed, which both remained significant in fully adjusted models. Links to other biomarkers were non-significant.

CONCLUSIONS: Several inflammatory markers are linked to skeletal muscle mass in older adults, where detrimental or beneficial actions are indicated depending on the biomarker. While adherence to PA guidelines moderates some of these links, others seem unaffected by either PA and protein intake or metabolic risk status. Further research is needed to elucidate mechanisms underlying these observations.