Objectives: frail older adults may be more vulnerable to stressors, resulting in steeper declines in cognitive function. Whether the frailty-cognition link differs by cognitive domain remains unclear; however, it could lend insight into underlying mechanisms.

Methods: we tested whether domain-specific cognitive trajectories (clock-drawing test, (CDT), immediate and delayed recall, orientation to date, time, president and vice-president naming) measured annually (2011-2016) differ by baseline frailty (physical frailty phenotype) in the National Health and Aging Trends Study (n = 7,439), a nationally representative sample of older adult U.S. Medicare beneficiaries, using mixed effects models to describe repeated measures of each cognitive outcome. To determine if the association between frailty and subsequent cognitive change differed by education, we tested for interaction using the Wald test.

Results: we observed steeper declines for frail compared to non-frail participants in each domain-specific outcome, except for immediate recall. Largest differences in slope were observed for CDT (difference = -0.12 (standard deviations) SD/year, 95%CI: -0.15, -0.08). By 2016, mean CDT scores for frail participants were 1.8 SD below the mean (95%CI: -1.99, -1.67); for non-frail participants, scores were 0.8 SD below the mean (95%CI: -0.89, -0.69). Associations differed by education for global cognitive function (Pinteraction < 0.001) and for each domain-specific outcome: CDT (Pinteraction < 0.001), orientation (Pinteraction < 0.001), immediate (Pinteraction < 0.001) and delayed (Pinteraction < 0.001) word recalls.

Conclusion: frailty is associated with lower levels and steeper declines in cognitive function, with strongest associations for executive function. These findings suggest that aetiologies are multifactorial, though primarily vascular related; further research into its association with dementia sub-types and related pathologies is critical.