Moderation effect of handgrip strength on cognition and functional independence associations in adults over 90 years

Introduction: The causal relationship between cognitive impairment and functional decline seems bidirectional in older adults. This study aimed to determine the moderating effect of handgrip strength on the relationship between cognition and functional independence among Brazilian nonagenarians and centenarians. Methods: A cross-sectional study was performed on 150 older adults aged > 90 years (141 nonagenarians and nine centenarians). A total of 105 participants (70%) were female. Cognitive function was assessed using the Mini-Mental State Examination (MMSE), and functional independence was evaluated using the Katz Index score. The maximal isometric grip strength was measured using a handgrip dynamometer. A moderation analysis was performed to test whether handgrip strength moderated the association between cognition and functional independence, stratified by biological sex and adjusted for body weight. Results: Handgrip strength moderated the relationship between cognition and functional independence in both male and female older adults (p < 0.05). When handgrip strength was < 24.40 kg for males (42% of the study sample) and < 17.30 kg for female participants (60% of the study sample), the influence of cognitive function on functional independence was significant. Conclusion: Handgrip strength moderates the relationship between cognition and functional independence in Brazilian nonagenarians and centenarians. This attenuating effect of muscle strength on the impact of cognitive function on functional independence was observed in both weaker male and female individuals. Longitudinal studies are needed to validate our findings, as the cross-sectional design limits the causal inferences.