Control of Blood Pressure Reduces Dementia Risk
Raised blood pressure produces damage to tissues throughout the body. That control of blood pressure via antihypertensive drugs, forcing better function without addressing any of the underlying causative damage of aging, does in fact reduce mortality in later life is a compelling indication of the degree to which raised blood pressure is directly harmful. In the brain, manifestations of this harm include an acceleration of the processes of atherosclerosis, disruption of the blood-brain barrier leading to brain inflammation, and an increase in the pace at which capillaries and other small vessels rupture, all of this damage contributing to the onset and progression of neurodegeneration and loss of cognitive function.
Dementia is fast becoming a global epidemic, currently affecting an estimated 50 million people worldwide. While many trials have looked at the health benefits of lowering blood pressure, not many included dementia outcomes and even fewer were placebo-controlled - considered to provide the best level of evidence. "Most trials were stopped early because of the significant impact of blood pressure lowering on cardiovascular events, which tend to occur earlier than signs of dementia."
To examine the relationship between blood pressure and dementia more closely, researchers analysed five double-blind placebo-controlled randomised trials that used different blood pressure lowering treatments and followed patients until the development of dementia. A total of 28,008 individuals with an average age of 69 and a history of high blood pressure from 20 countries were included. Across these studies, the mid-range of follow up was just over four years. After a median follow-up of 4.3 years, there were 861 cases of incident dementia. Regression analysis reported an adjusted odds ratio 0.87 in favour of antihypertensive treatment reducing risk of incident dementia with a mean blood pressure lowering of 10/4 mmHg.
"Our results imply a broadly linear relationship between blood pressure reduction and lower risk of dementia, regardless of which type of treatment was used. Our study provides the highest grade of available evidence to show that blood pressure lowering treatment over several years reduces the risk of dementia, and we did not see any evidence of harm. But what we still don't know is whether additional blood pressure lowering in people who already have it well-controlled or starting treatment earlier in life would reduce the long-term risk of dementia."