Eligible participants will have the option to participate in the core ADCC study and also in a biomarker-intensive substudy that will collect additional measurements of brain function and chemical markers of AD pathology. While all participants enrolled in the core ADCC study will receive brain magnetic resonance imaging (MRI) and a DEXA scan to measure fat and bone densities within the body, those enrolled in the substudy will complete a lumbar puncture (LP) to permit quantification of AD biomarkers in cerebrospinal fluid (CSF). Participants enrolled in the substudy will be referred to as the Biomarker-Intensive Group, or ADCC-BIG.