50-year-olds who have blood pressure that is higher than normal but still below the threshold commonly used when deciding to treat the condition, are at increased risk of developing dementia in later life, finds a new study led by UCL and French National Institute of Health and Medical Research in Paris (INSERM) researchers.
This increased risk was seen even when the study participants did not have other heart or blood vessel-related problems, according to the research, part of the long-running UCL-based Whitehall II study of over 10,000 civil servants, published today in the European Heart Journal.
Although there have been previous studies that have linked raised blood pressure in midlife to an increased risk of dementia in later life, the term ’midlife’ has been poorly defined and ranged from 35 to 68 years.
"Previous research has not been able to test the link between raised blood pressure and dementia directly by examining the timing in sufficient detail. In our paper we were able to examine the association at age 50, 60 and 70, and we found different patterns of association. This will have important implications for policy guidelines, which currently only use the generic term ’midlife’," said the first author of the paper, Dr Jessica Abell (UCL Epidemiology & Public Health and INSERM).
Participants in the Whitehall II study, who were aged between 35-55 in 1985, had their blood pressure measured in 1985, 1991, 1997 and 2003.
Among the 8,639 people analysed for this study, 385 developed dementia by 2017, at an average age of 75. Those who had a systolic blood pressure of 130 mmHg or more at the age of 50 had a 45% greater risk of developing dementia than those with a lower systolic blood pressure at the same age. This association was not seen at the ages of 60 and 70, and diastolic blood pressure was not linked to dementia.
The researchers say that more research is need to clarify whether effective management of high blood pressure in people in mid-life might weaken the risk of later dementia.
The link between high blood pressure and dementia was also seen in people who had no heart or blood vessel-related conditions (cardiovascular disease) during the follow-up period.
Guidelines from NICE (National Institute for Health and Care Excellence) in the UK and the European Society of Cardiology both give a threshold of 140/90 mmHg for hypertension, although 2017 guidelines from the American Heart Association, the American College of Cardiology and nine other health organisations lowered the threshold to 130/80 mmHg for all adults. Ideal blood pressure is considered to be between 90/60mmHg and 120/80mmHg.
Lead author Professor Archana Singh-Manoux (UCL Epidemiology & Public Health and INSERM) said: "Our work confirms the detrimental effects of midlife hypertension for risk of dementia, as suggested by previous research.
"Our analysis suggests that the importance of mid-life hypertension on brain health is due to the duration of exposure. So we see an increased risk for people with raised blood pressure at age 50, but not 60 or 70, because those with hypertension at age 50 are likely to be ’exposed’ to this risk for longer."
Possible reasons for the link between raised blood pressure and dementia include the fact that high blood pressure is linked to silent or mini strokes (where symptoms often are not noticeable), damage to the white matter in the brain, which contains many of the brain’s nerve fibres, and restricted blood supply to the brain. This damage may underlie the resulting decline in the brain’s processes.
Dr Abell said: "It is important to emphasise that this is observational, population-level research and so these findings do not translate directly into implications for individual patients. There is plenty of evidence to suggest that maintaining a healthy blood pressure in middle age is important for both your heart and your brain later in life. Anyone who is concerned about their blood pressure levels should consult their GP."
"One of the strengths of this study was having repeat blood pressure measurements on the same people, which allowed us to examine their blood pressure status over an 18-year period. This is rare, since previous research has often used a single measure of hypertension," concluded Professor Singh-Manoux.