Muscle degeneration and cognitive decline among Chinese older adults

Abstract

As age-related syndromes, sarcopenia and neurodegenerative disorders develop insidiously and are associated with poor health outcomes. To date, the pooled prevalence of sarcopenia among older Chinese in communities is well-reported, but estimates in clinical settings and nursing home settings remain unknown. Besides, epidemiological information about possible sarcopenia among Chinese community-dwelling older adults is limited. Handgrip strength (HGS) asymmetry may be useful to predict impaired neurocognitive function, but no research examines its association with neurodegenerative disorders. Furthermore, although motoric cognitive risk syndrome (MCR) is a simple tool for identifying dementia risk at the population level, assessing gait speed may burden primary care services and MCR subtypes with motoric domains more conveniently measurable are under-explored. Moreover, both low HGS and abdominal obesity (AO) are associated with cognitive impairment. However, it remains unclear whether low HGS and AO interact to affect cognition, and whether the interaction varies by gender.

The first objective of this thesis was to estimate the pooled prevalence rates of sarcopenia among older Chinese in different settings separately and explain the heterogeneity. The second to fifth objectives focused on the community-dwelling older Chinese and were to investigate the prevalence, incidence, and associated factors of possible sarcopenia; examine the association between HGS asymmetry and incident neurodegenerative disorders; examine associations between HGS-based MCR subtypes and incident cognitive impairment; and examine the gender-specific moderating role of AO on the association between low HGS and incident cognitive impairment.

I first performed meta-analysis to estimate the pooled sarcopenia prevalence among Chinese older adults in communities, hospitals, and nursing homes separately, and used meta-regression to identify factors of the heterogeneous estimates. Then, based on the community-dwelling sample from the China Health and Retirement Longitudinal Study, I investigated associated factors of the prevalence and incidence of possible sarcopenia using multivariable logistical model and parametric proportional hazard model. Next, I performed competing risk analysis to examine the association between HGS asymmetry and incident neurodegenerative disorders. I then examined associations between HGS-based MCR subtypes and incident cognitive impairment using the Cox proportional hazards model. Finally, I examined the gender-specific interaction between low HGS and AO on incident cognitive impairment using a subdistribution hazards model.

The pooled sarcopenia prevalence in communities, hospitals, and nursing homes was 12.9%, 29.7%, and 26.3% among men, and 11.2%, 23.0%, and 33.7% among women. Meta-regression showed different settings might explain the heterogeneous prevalence of sarcopenia among both genders, whereas assessment methods of muscle mass and regions might explain it among men only. In our study, 46% of community-dwelling older adults had possible sarcopenia, with the four-year incidence of 11.9 per 100 person-years. Advancing age, not receiving education, physical inactivity, and depression symptoms were associated with the higher prevalence or incidence of possible sarcopenia. HGS asymmetry and HGS-based MCR subtypes were associated with an increased risk of neurodegenerative disorders or cognitive impairment. Low HGS combined with AO was associated with the elevated risk of cognitive impairment among older men, but not in women.

Chinese older adults, particularly those in hospitals and nursing homes, are vulnerable to sarcopenia. Besides, a large proportion of Chinese community-dwelling older adults suffer from possible sarcopenia. Early sarcopenia screening and timely lifestyle intervention are recommended for at-risk populations. HGS asymmetry and HGS-based MCR subtypes may be considered in the early risk detection of neurodegenerative disorders or cognitive impairment. AO and low HGS may interact to increase the risk of cognitive impairment among Chinese older men. Screening the highest-risk subpopulation, who may benefit most from neurocognitive prevention strategies, may maximize potential public health gains.