Functional decline in cognitive impairment--the relationship between physical and cognitive function.

Background: Physical function decline is associated with dementia, which might either be mediated by the coexisting sarcopenia or directly related to the impaired cognition. Our objectives are to examine the relationship between cognitive function and performance-based physical function and to test the hypothesis that cognitive function is related to poor physical function independent of muscle mass.

Methods: We measured muscle strength, performance-based physical function and muscle mass using dual-energy X-ray absorptiometry and cognitive function using the cognitive part of the Community Screening Instrument of Dementia (CSI-D) in 4,000 community-dwelling Chinese elderly aged >65 years. A CSI-D cognitive score of >28.40 was considered as cognitively impaired. The effect of cognitive impairment on muscle strength and physical function was analyzed by multivariate analysis with adjustment for age, appendicular skeletal mass (ASM), the Physical Activity Scale for the Elderly (PASE) and other comorbidities.

Results: In both genders, the cognitively impaired (CSI-D cognitive score >28.40) group had a weaker grip strength (-5.10 kg, p < 0.001 in men; -1.08 kg in women, p < 0.001) and performed worse in the two physical function tests (in men, 6-meter walk speed, -0.13 m/s, p < 0.001, chair stand test, 1.42 s, p < 0.001; in women, 6-meter walk speed, -0.08 m/s, p < 0.001, chair stand test, 1.48 s, p < 0.001). After adjustment for age, ASM, PASE and other comorbidities, significant differences in grip strength (-2.60 kg, p < 0.001 in men; -0.49 kg, p = 0.011 in women) and the two physical function tests persisted between the cognitively impaired and nonimpaired group (in men, 6-meter walk speed, -0.072 m/s, p < 0.001, chair stand test, 0.80 s, p = 0.045; in women, 6-meter walk speed, -0.049 m/s, p < 0.001, chair stand test, 0.98 s, p < 0.001).

Conclusions: Poor physical function and muscle strength coexisted with cognitive impairment. This relationship was independent of muscle mass. It is likely therefore that the functional decline in dementia might be related directly to factors resulting in cognitive impairment independently of the coexisting sarcopenia.