High blood pressure is associated with many health conditions such as dementia, stroke, and heart attacks. Treating and managing high blood pressure may prevent such conditions, especially by maintaining a healthy brain.
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High Blood Pressure and Health
Blood pressure is the mechanism by which blood can flow throughout the body in arteries to reach the organs and bodily extremities. Normal blood pressure is considered anywhere in the range of between 90/60mmHg – 120/80mmHg.
Having high blood pressure, also known as hypertension, is when the pressure is above 140/90mmHg. Whilst we may all have hypertension from time to time, having persistently high blood pressure can cause many adverse effects to the body, including the brain.
The commonest causes of hypertension include a high sodium (salt) intake, obesity or being overweight leading to atherosclerosis (thickening and stiffening of arteries), excessive alcohol intake, sedentary lifestyle (physical inactivity), advanced age, family history of hypertension due to genes, being of African American or South Asian descent, and finally being male before 55 years of age, or female after 55 years of age.
Typically, having hypertension does not result in any noticeable symptoms, and only regular blood pressure readings can reveal the presence of hypertension. Symptoms would only occur until health complications occur due to uncontrolled hypertension.
Typically, these include peripheral arterial disease, retinal damage, chronic kidney disease, heart attacks, and heart failure in extreme cases.
High Blood Pressure and the Brain
In addition to all the complications listed above, chronic hypertension can also lead to several potentially fatal conditions in the brain, such as aneurysms and stroke. If these are smaller and persistent (such as a transient ischaemic attack, or cerebral small vessel disease), they can lead to vascular dementia and other dementias, which tend to have poor prognoses and are often incurable.
A recent study published in The Lancet Neurology investigated structural alterations to the brain by performing MRI, functional changes by PET imaging as well as cognitive assessments in a group of 502 individuals aged between 69-71 in the UK (none which had dementia).
Previously, blood pressure measurements were taken at the ages of 36, 43, 53, 60, and 69 years. Having higher blood pressure at 53 years and having a greater increment in blood pressure between 43 and 53 years was associated with brain white matter hyperintensity volumes (WMHV).
Specific increments in diastolic blood pressure from 36-43 years were associated with a smaller whole-brain volume at 70 years of age, whereas greater increments to systolic blood pressure between 36 and 43 years were associated with smaller hippocampal volumes at 70.
At the age of 70 years, these observations were not associated with beta-amyloid levels or significantly poor cognitive assessment scores.
However, this study indicates profound structural changes to the brain as a result of hypertension and greater increments in blood pressure. These may lead to the onset of dementia within the decade or so – which was not investigated by this study at this stage.
Improving Brain Health by Controlling Blood Pressure
Several epidemiological studies have posited hypertension as a primary risk factor for cerebral small vessel ischaemic disease (SVID) and white matter lesions (WMLs).
These themselves are associated with cognitive decline and onset of Alzheimer’s and other dementias. Based on the above study, one would speculate if blood pressure was carefully controlled from early and mid-life (mid-30s-mid-40s), then brain health would be maintained.
A recent study published in JAMA performed an MRI study on hypertensive adults over the age of 50 in the US, imaging 670 people at baseline and 449 after a 4 year follow up.
Two types of treatment strategies were randomly allocated: achieving a systolic blood pressure less than 120mmHg (intensive treatment) or less than 140mmHg (standard treatment).
The primary outcome of this study was a change in the total WML volume from baseline (i.e. how much of an increase of WML would occur).
The group receiving the harsher intensive antihypertensive treatment showed a WML volume increase from 4.57 to 5.49cm3 compared to a WML volume increase from 4.40 to 5.85cm3 for those receiving standard antihypertensive treatment.
That is a difference of +0.92cm3 for the intensive treatment compared to +1.45cm3 for the standard treatment. The mean total brain volume decrease change in the intensive group was -30.6cm3 compared to a decrease of -26.9cm3 for the standard group (difference of -3.7cm3).
This study shows overall that targeting hypertension leads to a smaller increase in WML volume in the brain, but a greater decrease in total brain volume overall. Whilst there are differences between an intensive vs standard antihypertensive treatment strategy, these differences are small.
The anatomical difference in greater brain volume loss is still unclear, though it is known blood pressure is associated with smaller brain volumes.
This study shows that hypertension is indeed a major risk factor for WML development, and a course of antihypertensive treatment successfully slows down WML development and progression, thus potentially delaying the onset of cognitive decline.
In summary, having a persistently high blood pressure over 140/90 (chronic hypertension) is associated with many potentially devastating neurological conditions such as stroke and dementia.
Having hypertension in early-mid-life and having higher increments in high blood pressure is associated with greater structural abnormalities in the brain that could be associated with cognitive declines, such as white-matter lesion burden.
Managing high blood pressure throughout midlife (reducing from 140 to 120) is associated with beneficial outcomes to WML in the brain that could potentially delay the onset of cognitive decline. Managing blood pressure is not only beneficial for brain health but overall cardiovascular health.