According to a 2013 study Oxysterols in the pathogenesis of major chronic diseases, hypercholesterolemia (specifically oxidized cholesterol) is a primary risk factor for Alzheimer's disease.

Oxidized cholesterol can penetrate the blood brain barrier, allowing long - term accumulation within the brain. This process is enhanced by an oxidative imbalance in the body (lack of antioxidants).

According to a 2012 study, plaque build up in the brain is a larger indicator of Alzheimer's progression than the APOE gene, often associated with the disease. It's just that testing for genotypes is easier than plaque imaging.

Brain autopsies in Alzheimer's patients show significantly more plaque build up in age-controlled brains vs controls. This study "strongly suggest that atherosclerosis-induced brain hypoperfusion (lack of blood flow) contributes to the clinical and pathological manifestations of AD."