The relationship between blood pressure and Alzheimer’s disease is complex. However, we do know that blood pressure raised in mid-life (hypertension) is a risk for the development of Alzheimer’s disease later on. Uncontrolled hypertension is a risk for dementia in general. In fact, stroke related dementias are primarily caused by either clotting or small bleeds in the brain. Hypertension can lead to bleeding, primarily in the brain, but can also damage the heart triggering the release of small clots that lodge in the brain, thus depriving the nerve cells (neurons) of oxygen supply.
It remains unclear to scientists why hypertension is a risk for Alzheimer’s disease, but we do know that in spontaneously hypertensive rats, there is a tendency to accumulate some of the pathology of Alzheimer’s disease.
In 1996, researchers at the Roskamp Institute discovered that the causative protein in Alzheimer’s (the amyloid protein) has a drastic effect on blood vessels. The effect is to increase the propensity of blood vessels to constrict. Subsequently, others show that after a small stroke (when blood vessels close down temporarily) the presence of amyloid tends to keep the blood vessels closed. It is assumed that the consequence of reduced blood flow to the brain, secondary to closed blood vessels, causes deprivation of oxygen and glucose to the neurons, thus causing more damage in a brain with high amyloid levels than one with not.
Translated into clinical terms, this means that the effect of a small stroke on somebody who is in the early stages of Alzheimer’s can be more devastating than somebody who is not. In fact, a study of nuns who were asked to complete mental state questionnaires in life and who subsequently died has revealed an important interaction between small strokes and the clinical signs of Alzheimer’s. Even though some nuns had amyloid deposits in their brain, they did not exhibit the symptoms of amyloid in life. Those nuns that had amyloid deposits but did exhibit the clinical symptoms of Alzheimer’s in life also had multiple small strokes.
Thus, damage to the blood vessels in the presence of amyloid is more devastating than if amyloid is absent. Hypertension tends to damage blood vessels throughout the body, but it is only in the brain that amyloid accumulates and can contribute to poor recovery after vascular injury.
What does this mean for patients treated at the Roskamp Institute? Patients are advised to take particular care to have their blood pressure and cardiovascular status monitored. High lipid or triglyceride levels can contribute to cerebrovascular (brain/blood vessel) damage and uncontrolled or poorly monitored high hypertension can also be highly detrimental. In addition, we know that other cardiac problems, such as arrhythmias can contribute to cerebrovascular damage, as mentioned, by throwing off small clots.
As we await effective treatments to combat Alzheimer’s directly, we need to ensure that we control other disorders which can contribute significantly to rapid declines in mental status. Interestingly, some antihypertensives seem to be able to control the risk for Alzheimer’s disease as well as controlling blood pressure.
Researchers at the Roskamp Institute have clearly shown that this does not apply to all antihypertensives and they are investigating why some are able to regulate both blood pressure and can reduce the incidence of Alzheimer’s disease while others cannot. This is an important area of research and clearly one that holds out hope for Alzheimer’s sufferers as the search for new treatments continues.