Cognitive Reserve and Mild Cognitive Impairment: Predictors and Rates of Reversion to Intact Cognition vs Progression to Dementia.

Little is known about the effect of education or other indicators of cognitive reserve on the rate of reversion from mild cognitive impairment (MCI) to normal cognition (NC), or the relative rate of reversion from MCI to NC vs. progression from MCI to dementia. Our objectives were to: 1) estimate transition rates from MCI to NC and dementia, and 2) determine the effect of age, apolipoprotein E (APOE), and indicators of cognitive reserve on the relative rate (RR) of reversion vs. progression using multistate Markov modelling.We estimated instantaneous transition rates between NC, MCI and dementia after accounting for transition to death across up to 12 assessments in the Nun Study, a cohort study of religious sisters aged 75+ years. We estimated RRs of reversion vs. progression for age, APOE, and potential cognitive reserve indicators: education, academic performance (high school grades), and written language skills (idea density, grammatical complexity).Of the 619 participants, 472 were assessed with MCI during the study period. Of these 472, 143 (30.3%) experienced at least one reverse transition to NC, and 120 of the 143 (83.9%) never developed dementia (mean follow-up=8.6 years). In models adjusted for age group and APOE, higher levels of education more than doubled the RR ratio of reversion vs. progression. Novel cognitive reserve indicators were significantly associated with a higher adjusted RR of reversion vs. progression (higher vs. lower levels for English grades: RR Ratio = 1.83; idea density: RR ratio=3.93; and grammatical complexity: RR ratio=5.78).Knowledge of frequent reversion from MCI to NC may alleviate concerns of inevitable cognitive decline in those with MCI. Identification of characteristics predicting the rate of reversion from MCI to NC vs. progression from MCI to dementia may guide population-level interventions targeting these characteristics to prevent or postpone MCI and dementia. Research on cognitive trajectories would benefit from incorporating predictors of reverse transitions and competing events, such as death, into statistical modelling. Finally, these results may inform the design and interpretation of MCI clinical trials, given that a substantial proportion of participants may experience improvement without intervention.