The Demographic and Medical Correlates of Plasma Aβ40 and Aβ42

Plasma amyloid -42 (A42) and A42/A40 are increasingly recognized as biomarkers for dementia, with low levels indicating increased risk. Little is known about the demographic and medical correlates of plasma A40 or A42. In 997 community-dwelling, nondemented older adults from the Health, Aging, and Body Composition Study, we determined the cross-sectional association between a wide range of demographic and medical variables with A40 and A42. In multivariate stepwise linear regression models, A40 was significantly associated with race (=-14.70, F=22.01, P<0.0001), age (=1.34, F=6.39, P=0.01), creatinine (=52.91, F=151.77, P<0.0001), and the serum brain-derived neurotrophic factor (=-0.0004, F=7.34, P=0.007); A42 was significantly associated with race (=-3.72, F=30.83, P<0.0001), sex (=1.39, F=4.32, P=0.04), education (=1.50, F=4.78, P=0.03), apolipoprotein E e4 genotype (=-2.82, F=16.57, P<0.0001), and creatinine (=9.32, F=120.09, P<0.0001). These correlates should be considered as potential confounders in future studies investigating plasma A as a biomarker of dementia. Understanding fully how these correlates mediate or modify the association between plasma A and dementia will be a fundamental step in determining the biological pathways through which plasma A40 and A42 are associated with dementia, and in determining their full potential as biomarkers.