Fig. 2.

Aging: the cause, a contributor or a confounder of Alzheimer’s disease? a Age is the dominant risk factor in Alzheimer’s disease. Recently it was suggested by two groups that accelerated biological aging is associated with cognitive decline [12, 16]. Based on current available data, it cannot be distinguished whether accelerated biological aging is a cause (upper scenario), contributor (mid scenario) or confounder (lower scenario) of Alzheimer’s disease. Red-framed text-boxes indicate cause(s). b Longitudinal cohort studies are necessary to determine whether biological aging is the cause, a contributor or a confounder of Alzheimer’s disease, and possibly to find other new sensitive and specific predictive markers capable of describing the start and length of the preclinical incubation period of Alzheimer’s disease within an individual. *Start of pathological process; preclinical, asymptomatic phase of AD; **start of clinical, symptomatic AD. AD Alzheimer’s disease. Red arrow with series of red triangles Samples taken during longitudinal study. (Color figure online)