Controlling Hypertension Reduces Dementia Risk, but Only if Done Early
The connection between raised blood pressure and dementia is well established. Controlling hypertension via the usual combination of lifestyle choice and medications slows cognitive decline, and any number of epidemiological studies show that dementia patients are more likely to have a history of hypertension. The data noted in this review is interesting for making the point that the pressure damage to the brain and its vasculature that results from high blood pressure occurs over the course of late life, and thus reducing blood pressure has little to no effect on patients already exhibiting dementia. This is one of many areas in aging in which prevention is key, and it is well worth considering that hypertension contributes to overall mortality, not just to incidence of dementia.
Mid-life hypertension is reported to be a factor inducing dementia. Mid-life is typically defined as 45-64 years old. In this manuscript, mid-life hypertension means hypertension in individuals approximately 50 years old, and late-life hypertension means hypertension in those approximately more than 70 years old. The Atherosclerosis Risk in Communities (ARIC) cohort showed that high blood pressure in mid-life (around 48-67 years old) induces poorer cognitive function or dementia 20 years later. Moreover, the Honolulu Heart Program or Honolulu Asia Aging Study demonstrated that subjects less than 50 year old, even those with prehypertension, had an increased risk for dementia only in the untreated group.
Interestingly, subjects receiving antihypertensive medication showed no increased risk for dementia, even in those with systolic blood pressure of more than 140 mmHg, indicating that early intervention in hypertension is one approach to prevent late-life dementia. So, what is the target level of blood pressure in mid-life to prevent dementia? It was reported that systolic blood pressure elevation at age 50 years is associated with increased risk of dementia. Moreover, a systolic blood pressure level of 130 mmHg or lower has been shown to significantly prevent dementia at age 50. However, blood pressure elevation at 60 or 70 years old is not a significant risk, even in those with severe high blood pressure.
On the other hand, intervention for high blood pressure in the very elderly did not significantly reduce the incidence of dementia in the Hypertension In the Very Elderly Trial-COGnitive function assessment (HYVET-COG) trial. Moreover, the HYVET cohort study demonstrated that orthostatic hypotension indicates an increased risk of dementia and cognitive decline. Thus, intensive blood pressure treatment to prevent dementia is not recommended in "very elderly people" because blood pressure lowering fails to maintain cerebral blood flow because of dysfunction of cerebral autoregulation. Therefore, the younger the age at which blood pressure is managed at an appropriate level the better in order to prevent cognitive decline.