It is well known that hypertension, raised blood pressure, results in greater risk of a range of age-related conditions, particularly cognitive decline and dementia. The mechanisms of interest include damage to the blood-brain barrier, allowing unwanted molecules and cells into the brain, where they can spur chronic inflammation, and rupture of small blood vessels in the brain, resulting in microbleeds that are effectively tiny strokes, destroying small regions of tissue. Over time, this all adds up, and is why even methods that force a lowering of blood pressure without addressing the underlying causes of hypertension can produce a sizable reduction in risk of age-related disease and mortality. As noted in the data presented here, this is a matter of accumulated damage over time, so maintaining a lower blood pressure is a life-long concern.
In a study that spanned two and a half decades and looked at data from more than 4,700 participants, researchers have added to evidence that abnormal blood pressure in midlife persisting into late life increases the likelihood of developing dementia. Although not designed to show cause and effect, the study suggests that maintaining a healthy blood pressure throughout life may be one way to help decrease one's risk of losing brain function. In their study, they found that those people with the high blood pressure condition hypertension during middle age and during late life were 49% more likely to develop dementia than those with normal blood pressure at both times. But, putting one at even greater risk was having hypertension in middle age and then having low blood pressure in late life, which increased one's dementia risk by 62%.
High blood pressure was considered any measurement more than 140/90 millimeters of mercury, whereas low blood pressure was defined as less than 90/60 millimeters of mercury. A cognitive exam, caregiver reports, hospitalization discharge codes, and death certificates were used to classify participant brain function and determine cognitive impairment. High blood pressure can be genetic, but can also be the result of not enough exercise and poor diet. As people age, the top blood pressure number (systolic) oftentimes increases while the bottom number (diastolic) can decrease due to structural changes in the blood vessels. Dementia itself may lead to a lowering of blood pressure, as it may disrupt the brain's autonomic nervous system. Further, stiffening of the arteries from disease and physical frailty can also lead to low blood pressure in late life.