Blood biomarkers of Alzheimer's disease and 12-year muscle strength trajectories in community-dwelling older adults: a cohort study

Background: Age-related muscle function decline is a major impediment to healthy ageing. We aimed to investigate the association between a panel of Alzheimer's disease-related biomarkers and longitudinal trajectories of muscle strength, while exploring the influence of cognitive function. Methods: In this cohort study, we gathered data from the Swedish National study on Aging and Care in Kungsholmen (SNAC-K), an ongoing prospective study that includes adults aged 60 years and older, from central Stockholm, Sweden. We included data from baseline to the fourth follow-up (March 21, 2001, to Dec 31, 2016). Seven Alzheimer's disease-related blood biomarkers were measured in dementia-free, community dwelling participants: total tau, phosphorylated tau181 (p-tau181), phosphorylated tau217 (p-tau217), amyloid β 40 and 42, neurofilament light chain, and glial fibrillary acidic protein (GFAP). Muscle strength was measured through the handgrip strength and chair-stand tests. Linear mixed models were used to explore the association between baseline Alzheimer's disease-related biomarkers and muscle strength trajectories. Findings: The baseline SNAC-K cohort included 3363 individuals, of whom 1953 participants were included in our analyses (mean age 70·2 [SD 9·1] years; 780 [39·9%] male and 1173 [60·1%] female participants). In adjusted models, higher concentrations of p-tau181 (β per year 0·93 [95% CI 0·71 to 1·16]; p<0·0001), p-tau217 (β per year 1·31 [1·03 to 1·58]; p<0·0001), neurofilament light chain (β per year 0·76 [0·56 to 0·96]; p<0·0001), and GFAP (β per year 0·37 [0·21 to 0·53]; p<0·0001) were associated with an accelerated decline of chair-stand performance over time. The adjustment for Mini-Mental State Examination (MMSE) score led to the attenuation of these associations. Higher concentrations of p-tau181 (β per year –0·12 [95% CI –0·17 to –0·07]; p<0·0001), p-tau217 (β per year –0·13 [–0·20 to –0·07]; p<0·0001), and neurofilament light chain (β per year –0·05 [–0·09 to –0·001]; p=0·047) were also associated with faster handgrip strength decline, with no attenuation after adjusting for MMSE score. Sex-specific differences were observed, with female participants showing a stronger association between biomarker concentrations and muscle strength decline than male participants, particularly in the chair-stand test. Interpretation: Our findings suggest that blood Alzheimer's disease-related biomarkers might help estimate progressive muscle strength decline among older adults, elucidating the influence of brain pathology and cognitive ageing on this association. These Alzheimer's disease-related biomarkers could aid in identifying individuals for early intervention to prevent sarcopenia. Funding: The Swedish Research Council, the Swedish Ministry of Health and Social Affairs, and the County Councils and Municipalities.