Sex differences in the association between muscle quality, inflammatory markers, and cognitive decline

Abstract

Objective: Aspects of frailty such as sarcopenia and dementia are associated with a proinflammatory state; however, little research has examined the concurrence of these pathologies. This study examined sex-specific differences in the relationship between low muscle quality and impaired cognitive functioning, while considering the role of inflammatory markers.

Design: The nationally representative sample was drawn from a cross-sectional study.

Participants: Four hundred forty-five females and four hundred twenty-two males over age 60 from the National Health and Nutrition Examination Survey for 2001-2002 were included.

Measurements: Muscle quality was calculated as isokinetic strength per unit muscle mass. Skeletal muscle mass of the legs was measured using dual energy x-ray absorptiometry and isokinetic strength of the knee extensors was estimated using a Kin-Com dynamometer. Participants were assessed for cognitive functioning using the Wechsler Adult Intelligence Scale, Third Edition (WAIS-III) Digit Symbol - Coding module. High sensitivity C-reactive protein (CRP) assays were performed on blood samples using a Behring Nephelometer to estimate levels of inflammation. Sex stratified ordinary least squares regression models were utilized to estimate the relationship between muscle quality and cognitive functioning, while examining CRP as a possible mechanism and controlling for potential confounds.

Results: In the first model a statistically significant positive relationship was found between cognitive functioning and muscle quality for both sex groups. In the second model, CRP was found to have a statistically significant negative association with cognitive functioning for females but not males. Furthermore, the inclusion of CRP in the second model significantly reduced the predictive power of muscle quality for females, as compared to model 1.

Conclusion: Measures of sarcopenia are associated with lower cognitive functioning in older adults, and for females, this association may be partly due to systemic inflammation. Further research is need to examine the relationship between these frailty-related pathologies, which have substantial health and economic implications.