ALB and Alzheimer disease: In terms of barrier functionality, by aging, the human BBB permeability increases, in particular to albumin,[91] with human albumin having a diameter of 8.5 nm.[92] During aging of the human brain, the BBB breakdown begins in the hippocampus, which leads to damage to pericytes.[93] However, the BBB permeability increases further in patients with either vascular dementia or AD compared with age‐matched controls.[91] There are several factors that contribute to the BBB breakdown by aging.