It is uncontroversial that the age-related deterioration of the vascular system leads to damage to the brain, causing cognitive decline and then dementia. Progressive stiffening due to cross-links and calcification and inflammation-driven remodeling of blood vessel walls reduces structural integrity at the same time as it causes hypertension, raised blood pressure that puts more stress on those same blood vessel walls. This paper presents a novel way of looking at this contribution to the aging process:
The brain and its blood vessels are very different tissues. The nerve and glial cells of the brain (its processing machinery) develop from the ectoderm of the embryo; the brain's blood vessels (its system of oxygen supply and metabolite removal) develop from mesoderm, growing from the heart to surround and then penetrate the developing brain. By birth, vessels have branched through every millimeter of brain tissue, and they become involved in most, if not all, diseases or injuries of the brain.
Age-related dementia has seemed, to Alois Alzheimer and to most observers since, to be a degeneration of the brain, of its nerve cells. This review brings together two bodies of evidence, from which we propose that the dementia is primarily vascular, caused by the destructive effective of the pulse on cerebral blood vessels, with the loss of neurons occurring secondarily to vascular breakdown. We argue, further, that dementia is age-related because the pulse becomes more intense and more destructive with age.
The idea is uncongenial and counterintuitive. It is uncongenial because it does not appear to offer a simple path to therapy, counter-intuitive because we are used to thinking of the brain as a dependent ward of the heart, not as a victim of its beat. The idea may be correct, however counter-intuitive, for its explanatory power is considerable. It links the puse to hemorrhage, and to the neuropathology and arteriosclerosis that Alzheimer described; it explains the link from age to dementia, in the stiffening of the walls of the great arteries, and the effect of that stiffening on blood pressure. Here we review the evidence that pulse-induced destruction of the brain, and of another highly vascular organ, the kidney, are becoming the default forms of death, the way we die if we survive the infections, cardiovascular disease, and malignancies, which still, for a decreasing minority, inflict the tragedy of early death.
There are, in fact, comparatively straightforward paths to therapies that can mitigate this contribution to the aging process, though at present their development is given far too little attention and support by the research community. Firstly prevent and reverse loss of elasticity in blood vessels, such as by breaking down persistent cross-links, and secondly target the mechanisms of atherosclerosis responsible for remodeling blood vessel walls to suppress inflammation and clear plaques. Target the root causes and natural repair mechanisms should do much to clean up the rest of the issue.