Associations of Skeletal Muscle Mass, Lower-Extremity Functioning, and Cognitive Impairment in Community-Dwelling Older People in Japan

ObjectiveWe examined whether skeletal muscle mass and lower extremity functioning are closely associated with multiple cognitive domains, including global cognition, memory, attention, executive functioning, and processing speed, in community-dwelling older Japanese adults.DesignA cross-sectional, population-based community study.SettingThis study was conducted among community-living older people enrolled in the Obu Study of Health Promotion for the Elderly.ParticipantsParticipants comprised 5,104 adults ( 65 years, mean age: 71 years).MeasurementsData from 4273 participants were analyzed. Appendicular skeletal muscle mass was estimated from bioelectrical impedance analysis and expressed as appendicular skeletal muscle mass index (ASMI). Lower-extremity functioning was assessed by the Five-Times-Sit-to-Stand test (FTSS) and Timed Up and Go test (TUG). Cognitive functions were assessed by the Mini Mental State Examination, word list memory, Trail Making Test parts A and B, and Symbol Digit Substitution Task. Logistic regression analysis were performed to calculate odds ratios (ORs) of cognitive impairment in various domains among skeletal muscle mass, lower-extremity functioning levels adjusted for important demographic variables, and comorbidities.ResultsParticipants with lower ASMI and slower FTSS and TUG groups had lower cognitive functioning scores than did participants with higher ASMI and faster FTSS and TUG. The slowest quartiles (Q4) of FTSS and TUG were significantly associated with impaired global functioning (MMSE score < 24) compared to the fastest quartile (Q1) after multivariate adjustment (FTSS, OR = 1.46, 95% confidence interval (CI) = 1.12-1.90; TUG, OR = 1.65, 95% CI = 1.25-2.17). In other dimensions of cognitive functioning, FTSS and TUG were significantly associated with all cognitive impairment in the full adjustment model.ConclusionLower-extremity functioning, rather than skeletal muscle mass, is closely related to multiple cognitive domains. This study suggests that maintaining lower-extremity functioning, rather than skeletal muscle mass, may be required for detecting and preventing cognitive impairment.