BACE1 and Alzheimer disease: It is now admitted that vitamin D reduces the accumulation of β-amyloid peptide in AD brains by (i) modulating the activity or expression of ADAM10, APP, BACE, Nicastrin, and Presenilin 1/2 [23, 29] and (ii) increasing its clearance by macrophages or through the brain-blood barrier [20, 60].