Association of Plasma Amyloid-β and Dementia Among Black and White Older Adults.

Background: Plasma amyloid-β (Aβ) has emerged as an important tool to detect risks of Alzheimer's disease and related dementias, although research in diverse populations is lacking. Objective: We compared plasma Aβ42/40 by race with dementia risk over 15 years among Black and White older adults. Methods: In a prospective cohort of 997 dementia-free participants (mean age 74±2.9 years, 55% women, 54% Black), incident dementia was identified based on hospital records, medication, and neurocognitive test over 15 years. Plasma Aβ42/40 was measured at Year 2 and categorized into low, medium, and high tertile. We used linear regression to estimate mean Aβ42/40 by race and race-stratified Cox proportional hazards models to assess the association between Aβ42/40 tertile and dementia risk. Results: Black participants had a lower age-adjusted mean Aβ 42/40 compared to White participants, primarily among APOE ɛ4 non-carriers (Black: 0.176, White: 0.185, p = 0.035). Among Black participants, lower Aβ 42/40 was associated with increased dementia risk: 33% in low (hazard ratios [HR] = 1.77, 95% confidence interval 1.09-2.88) and 27% in medium tertile (HR = 1.67, 1.01-2.78) compared with 18% in high Aβ 42/40 tertile; Increased risks were attenuated among White participants: 21% in low (HR = 1.43, 0.81-2.53) and 23% in medium tertile (HR = 1.27, 0.68-2.36) compared with 15% in high Aβ 42/40 tertile. The interaction by race was not statistically significant. Conclusions: Among community-dwelling, non-demented older adults, especially APOE ɛ4 non-carriers, Black individuals had lower plasma Aβ 42/40 and demonstrated a higher dementia risk with low Aβ42/40 compared with White individuals.