Capillaries, Old Age and Alzheimer’s Disease

Diminished blood flow to the brain and other organ systems may result from an impaired microcirculation due to pathological changes in the capillaries or reduced numbers of capillaries. The former are reflected in twisting, kinking, andlooping of capillaries in the cerebral cortex. Whether these changes progress to reduced capillary numbers by cellular atrophy has not been demonstrated and is not considered further here. However, the widespread reduced capillary density (CD) found in aged animals and people has been correlated with diminished levels of angiogenic growth factors (AGFs).

The association between CD and AGFs during old age is the focus of this essay, which advances two ideas. 1) The reduced CD of old age may be the main, primary cause of many symptoms and signs of the elderly, i.e., the ‘lesser ailments of aging’. 2) A reduced CD may also be an underlying, secondary condition for other diseases associated with aging and may facilitate the action of factors postulated to cause them -- e.g. amyloid plaques, neurofibrillary tangles, etc. of Alzheimer’s disease (AD) or Lewy bodies, proposed malfunctioning mitochondria, etc. of Parkinson’s disease (PD).