Higher than normal blood pressure is linked to more extensive brain damage in the elderly, a study finds.
The study, published in the European Heart Journal, found that there was a strong association between diastolic blood pressure (the blood pressure between heartbeats) 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 research, carried out by Dr Karolina Wartolowska, a clinical research fellow at the Centre for Prevention of Stroke and Dementia, University of Oxford, 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.”
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 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.
Dr Wartolowska said: ‘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.’
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.
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.’
Researchers said 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 heartbeat, rapid changes in blood pressure, and blood flow that is too low between heartbeats, resulting in damage to white matter.
As MRI scans were only available at a 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 potentially complex interaction between risk factors, which also include high cholesterol levels, obesity and kidney problems, require further investigation.
Dr Richard Oakley, head of research at Alzheimer’s Society, which part-funded the study, said we now need to work on understanding the steps we can take to prevent Alzheimer’s.
‘High blood pressure doesn’t just affect our hearts, but our heads too.
‘Although this study didn’t look for a specific link between blood pressure and dementia, it’s an important step forward in understanding how high blood pressure is linked to changes in the brain that can increase our risk of dementia.
‘With few dementia treatments available and researchers still searching for a cure, it’s vital we do what we can to keep our minds healthy, as well as our bodies.
‘The recent Lancet Commission report, the largest study into preventable risk factors for dementia, identified 12 factors that can increase our chances of dementia, including high blood pressure.
‘But the work’s not over, we still need to understand how and why this happens, and the steps needed to prevent this devastating condition. With one million people in the UK expected to be living with dementia within the next five years, we need continued investment in dementia research to make this happen.’
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