High diastolic blood pressure before the age of 50 years is linked to brain damage in later life, even if the diastolic blood pressure was within what is normally considered to be a healthy range.
The findings published in European Heart Journal come from 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.
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.
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.
He 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.
“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."
White matter hyperintensities associated with high blood pressure
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.
The researchers added that the 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.