Association of year-to-year grip strength variability with risk of cognitive trajectories: Longitudinal evidence from a nationally representative cohort study

Background: Grip strength is a reliable marker of overall muscle strength and nutritional status. This study aimed to investigate the relationship between year-to-year grip strength variability and subsequent cognitive trajectories among middle-aged and older Chinese adults. Methods: We analyzed longitudinal grip strength data from the first three waves (W1–W3) of the China Health and Retirement Longitudinal Study (CHARLS). Annual grip strength variations were assessed using the Variance Independent of Mean (VIM). To analyze the developmental trajectories of different subgroups in the longitudinal data, group-based trajectory modeling (GBTM) was used to systematically investigate age-related changes in cognitive aging trajectories. Associations between trajectory membership and grip strength variability were examined using multinomial logistic regression. Results: The study included 4205 participants aged 50–75 years, whose longitudinal cognitive trajectories were classified into four distinct patterns according to global cognitive performance. The largest subgroup, the “persistently high” trajectory (n = 1406, 33.4 %), maintained superior cognitive function throughout the follow-up period. A “fluctuating moderate” trajectory was identified in 976 participants (23.2 %), while the remaining participants were nearly evenly split between “persistently moderate” (n = 937, 22.3 %) and “persistently low” (n = 886, 21.1 %) trajectories, demonstrating stable intermediate and poor cognitive function, respectively. Participants exhibiting greater grip strength variability had significantly increased odds (odds ratio [OR]: 2.37, 95 % confidence interval [CI]: 1.69–3.30) of belonging to the “persistently low” trajectory of global cognitive function. Conclusions: The cumulative evidence from these analyses demonstrates that sustaining stable muscle strength over time is strongly associated with favorable cognitive aging outcomes. Elevated variability in grip strength was significantly linked to a higher likelihood of following a persistently low cognitive trajectory, regardless of overall trends or baseline values. Participants with high baseline grip strength who also exhibited low but increasing variability over time appeared to maintain a “persistently high” cognitive trajectory.