Lifetime risk of incident dementia and incident mild cognitive impairment in older adults.

Background and Objectives: To estimate the lifetime risk of dementia and mild cognitive impairment (MCI) from age 55 to 105, accounting for competing risk of death, and to examine differences by sex and race. Methods: We analyzed data from five harmonized longitudinal cohort studies at the Rush Alzheimer's Disease Center, including 4611 community dwelling older adults for lifetime dementia risk estimation and 3915 for lifetime MCI risk estimation. Incident dementia and MCI were identified through annual clinical evaluations. Nonparametric cumulative incidence function curves estimated lifetime risk, adjusting for competing risk of death and left truncation. Additional analyses assessed lifetime risk from index ages 55, 65, 75, and 85 and examined differences by sex and race. Results: The lifetime risk of incident dementia after age 55 was 43% (95% CI: 38-47), with a median age at diagnosis of 88 years(IQR: 83-92). For MCI, the lifetime risk was 62% (95% CI: 57-67), with a median age at diagnosis of 86 years(IQR: 80-90). Females had higher lifetime risks than males for both dementia (45% vs. 39%) and MCI (63% vs. 60%). Racial differences were smaller for dementia (45% in Black vs. 44% in White participants). For MCI, Black adults had higher lifetime risk before age 90. Discussion: These findings extend dementia lifetime risk estimation beyond age 90 among diverse older adults to provide lifetime risk estimates for MCI while accounting for the competing risk of death, highlighting the importance of prevention, and equitable public health strategies to reduce the burden of cognitive impairment.