High blood pressure (hypertension), especially in middle age, is a major contributor to cognitive decline and dementia later in life, according to a new Scientific Statement from the American Heart Association, published in the journal Hypertension. Its review of the research explains how hypertension can cause brain diseases such as stroke, vascular cognitive impairment, and dementia (including Alzheimer’s disease), and it highlights what is still not completely understood.
Vascular cognitive impairment involves a range of changes in brain function, from mild to severe, caused in part by impaired blood flow to the brain. The brain and its blood vessels are main targets for hypertension’s adverse effects, including oxidative stress, damage to white matter, brain atrophy, and strokes (microscopic or full-blown). Strokes, in turn, increase the risk of cognitive impairment and dementia.
“Hypertension is the most powerful modifiable risk factor for the cerebrovascular damage, and the dramatic reduction in stroke mortality over the past several decades has been attributed to the treatment of hypertension,” according to the authors. But while many clinical trials have shown that treatment of hypertension (usually with drugs) reduces the risk of strokes and other cardiovascular disease, the evidence supporting its beneficial effect on cognitive health has been largely observational and has not been able to prove cause and effect. One complication is that it can take decades for hypertension to cause cognitive problems, and clinical trials lasting that long are a difficult undertaking.
“Although robust evidence is lacking to prove that antihypertensive therapy in middle age provides a cognitive benefit, such a benefit appears likely,” the authors stated. “Given how prevalent hypertension is and that there are many accessible and effective drugs, treatment of hypertension may prove to be one of the best ways to prevent or delay dementia.”
The following questions remain unanswered: When is the optimal time to begin treating rising blood pressure in order to protect cognition (perhaps while it’s still in the prehypertension range) and how aggressive should the treatment be? When people have both hypertension and advanced cognitive impairment, will treating the former reverse the latter or at least slow its progression? How does hypertension interact with various genetic and neurodegenerative factors in the brain? Do specific classes of antihypertensive drugs confer greater cognitive benefits than others?
It’s hoped that results from the important NIH-sponsored SPRINT-MIND clinical trial, expected later in 2017, will fill some of the knowledge gaps concerning treatment of hypertension as a way to protect cognition. We’ll keep you informed about its findings.
Also see Cautious Hope for Dementia.