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Blood pressure below treatable threshold linked to heightened dementia risk

Risk evident among 50-year-olds in absence of other cardiovascular problems

Caroline White

Wednesday, 13 June 2018

“Midlife” blood pressure that is higher than normal but still below the threshold commonly used to treat the condition is linked to a heightened risk of developing dementia in later years, finds research* published today in the European Heart Journal.

The findings, which draw on the long-running Whitehall II study of over 10,000 civil servants, show that this risk was evident even in the absence of other cardiovascular problems.

Previous research has linked raised blood pressure in mid-life to an increased risk of dementia in later life, but “midlife” has been poorly defined and ranged in age from 35 to 68.

Study author Dr Jessica Abell, of the French National Institute of Health and Medical Research in Paris (INSERM) and a research associate in dementia and epidemiology at UCL, said that previous research had not been able to test the link between raised blood pressure and dementia directly by looking at the timing in sufficient detail.

“We were able to examine the association at ages 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’,” she explained.

The Whitehall II study participants, who were aged between 35 and 55 in 1985, had their blood pressure measured in 1985, 1991, 1997 and 2003. Other potentially important information was also recorded, including age, sex, lifestyle, such as smoking and drinking, household income, and educational attainment.

Among the 8639 people included in the analysis, around a third (32.5%) of whom were women, 385 had developed dementia by 2017.

A systolic blood pressure of 130 mmHg or more at the age of 50 was associated with a 45% greater risk of developing dementia than a lower systolic blood pressure at the same age.

This association was not seen at the ages of 60 and 70, nor was diastolic blood pressure linked to dementia risk. The average age at which dementia developed was 75.

The link between high blood pressure and dementia was also seen in people who had no cardiovascular disease during the monitoring period: they had an increased risk of 47% compared to people with systolic blood pressure below 130 mmHg at the age of 50.

Guidelines from the National Institute for Health and Care Excellence and the European Society of Cardiology both set a threshold of 140/90 mmHg for high blood pressure.

But 2017 guidelines from the American Heart Association, the American College of Cardiology, and nine other health organisations lowered this threshold to 130/80 mmHg for all adults. Ideal blood pressure is considered to be between 90/60 mmHg and 120/80 mmHg.

Professor Archana Singh-Manoux, research professor at INSERM and honorary professor at UCL, who led the research, said: “Our work confirms the detrimental effects of 'midlife' hypertension for risk of dementia, as suggested by previous research. It also suggests that at age 50, the risk of dementia may be increased in people who have raised levels of systolic blood pressure below the threshold commonly used to treat hypertension.

“Our analysis suggests that the importance of 'midlife' 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 associations found 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. Furthermore, there is considerable discussion on the optimal threshold for the diagnosis of hypertension. 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.”

Study limitations include the fact that dementia was diagnosed by linking to electronic medical records that might have missed milder cases; the researchers weren’t able to see whether the association was stronger with Alzheimer’s disease or vascular dementia because of the small numbers affected by dementia; nor were they able to glean whether effective management of high blood pressure in "midlife" might weaken the risk of dementia later on.

Nevertheless, Professor Singh-Manoux, concluded: “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.”

*Abell JG, Kivimäki M, Dugravot A, et al. Association between systolic blood pressure and dementia in the Whitehall II cohort study: role of age, duration and threshold used to define hypertension. European Heart Journal, published: 12 June 2018, doi: 10.1093/eurheartj/ehy288

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