Higher than normal blood pressure is linked to more extensive brain damage in the elderly, according to a new study published in the European Heart Journal.
In particular, the study
found that there was a strong association between diastolic blood pressure (the
blood pressure between heart beats) before the age of 50 and brain damage in
later life, even if the diastolic blood pressure was within what is normally
considered to be a healthy range.
The findings come from a
study of 37,041 participants enrolled in UK Biobank, a large group of people
recruited from the general population aged between 40 and 69 years, and for
whom medical information, including MRI brain scans was available.
The research, carried out by
Dr Karolina Wartolowska, a clinical research fellow at the Centre for
Prevention of Stroke and Dementia, University of Oxford, UK, looked for damage
in the brain called “white matter hyperintensities” (WMH). These show up on MRI
brain scans as brighter regions and they indicate damage to the small blood vessels
in the brain that increases with age and blood pressure. WMH are associated
with an increased risk of stroke, dementia, physical disabilities, depression
and a decline in thinking abilities.
Dr Wartolowska said: “Not all
people develop these changes as they age, but they are present in more than 50%
of patients over the age of 65 and most people over the age of 80 even without
high blood pressure, but it is more likely to develop with higher blood
pressure and more likely to become severe.”
Information on the
participants was collected when they enrolled in UK Biobank between March 2006
and October 2010, and follow-up data, including MRI scans, were acquired
between August 2014 and October 2019. The researchers adjusted the information
to take account of factors such as age, sex, risk factors such as smoking and
diabetes, and diastolic as well as systolic blood pressure. Systolic blood
pressure is the maximum blood pressure reached each time the heart beats and is
the top number in blood pressure measurements.
“To compare the volume of
white matter hyperintensities between people and to adjust the analysis for the
fact that people’s brains vary slightly in size, we divided the volume of WMH
by the total volume of white matter in the brain. In that way, we could analyse
the WMH load, which is the proportion of the WMH volume to the total volume of
white matter,” said Dr Wartolowska.
The researchers found that a
higher load of WMH was strongly associated with current systolic blood
pressure, but the strongest association was for past diastolic blood pressure,
particularly when under the age of 50. Any increase in blood pressure, even
below the usual treatment threshold of 140 mmHg for systolic and below 90 mmHg
for diastolic, was linked to increased WMH, especially when people were taking
medication to treat high blood pressure.
For every 10mmHg increase in
systolic blood pressure above the normal range, the proportion of WMH load
increased by an average (median) of 1.126-fold and by 1.106-fold for every
5mmHg increase in diastolic blood pressure. Among the top 10% of people with
the greatest WMH load, 24% of the load could be attributed to having a systolic
blood pressure above 120mmHg, and 7% could be attributed to having diastolic
blood pressure above 70mmHg, which reflects the fact that there is a greater
incidence of elevated systolic rather than diastolic blood pressure in older
patients.
Dr Wartolowska said: “We made
two important findings. Firstly, the study showed that diastolic blood pressure
in people in their 40s and 50s is associated with more extensive brain damage
years later. This means that it is not just the systolic blood pressure, the
first, higher number, but the diastolic blood pressure, the second, lower
number, that is important to prevent brain tissue damage. Many people may think
of hypertension and stroke as diseases of older people, but our results suggest
that if we would like to keep a healthy brain well into our 60s and 70s, we may
have to make sure our blood pressure, including the diastolic blood pressure,
stays within a healthy range when we are in our 40s and 50s.
“The second important finding
is that any increase in blood pressure beyond the normal range is associated
with a higher amount of white matter hyperintensities. This suggests that even
slightly elevated blood pressure before it meets the criteria for treating
hypertension has a damaging effect on brain tissue.
“Our results suggest that to
ensure the best prevention of white matter hyperintensities in later life,
control of diastolic blood pressure, in particular, may be required in early
midlife, even for diastolic blood pressure below 90mmHg, whilst control of
systolic blood pressure may be more important in late life. The long time
interval between the effects of blood pressure in midlife and the harms in late
life emphasises how important it is to control blood pressure long-term, and
that research has to adapt to consider the very long-term effects of often
asymptomatic problems in midlife.”
Potential mechanisms for the
development of WMH include damage to the delicate blood vessels in the brain
through sustained elevated pressures over time that directly cause damage to
the blood vessels; this leads to the lining of the vessels becoming leaky and
results in WMH. Alternatively, diastolic pressure might cause large blood
vessels to become stiffer with time, which increases pulsations of blood
pressure to the brain; this causes high blood pressure with each heart beat,
rapid changes in blood pressure, and blood flow that is too low between heart
beats, resulting in damage to white matter.
As MRI scans were only
available at one time point, the researchers could not quantify the progression
of WMH directly. Other limitations include that further analysis is needed to
identify differences in different regions of white matter, and that although
the researchers showed associations with smoking and diabetes, the potential
complex interaction between risk factors, which also include high cholesterol
levels, obesity and kidney problems, require further investigation.
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