Conscientiousness, dementia related pathology, and trajectories of cognitive aging.

The study aim was to determine the contribution of dementia related pathologies to the association of conscientiousness with late-life cognitive health. At enrollment in 2 longitudinal clinical-pathologic cohort studies, 309 older individuals without cognitive impairment completed a standard conscientiousness measure. Annually thereafter, they completed a battery of 17 cognitive tests. On death, they underwent a uniform neuropathologic examination from which measures of neurofibrillary tangles, Lewy bodies, chronic gross cerebral infarction, and hippocampal sclerosis were derived. The relation of conscientiousness and the neuropathologic markers to cognitive decline was assessed in mixed-effects change point models to accommodate nonlinear cognitive decline. During a mean of 10.7 years of follow-up, annual decline on a composite measure of global cognition (baseline M = 0.082, SD = 0.499) was gradual (estimated M = -0.036, 95% CI [-0.046, -0.025]) until a mean of 3.2 years before death (95% CI [-3.6, -2.8]) when it accelerated to a mean annual loss of 0.369 unit (95% CI [-0.426, -0.317]), a tenfold increase. Higher conscientiousness (baseline M = 33.6, SD = 5.1) was associated with slower terminal decline (estimate = 0.064, 95% CI [0.024, 0.103]) but not preterminal decline (estimate = 0.005, 95% CI [-0.003, 0.013]). After adjustment for neuropathologic burden, conscientiousness was still related to terminal decline (estimate = 0.057, 95% CI [0.019, 0.094]) and accounted for 4% of the variance in terminal slopes. In addition, the association of neocortical Lewy bodies with terminal cognitive decline was attenuated in those with higher conscientiousness. The results suggest that higher conscientiousness is protective of late-life cognitive health.