People with high blood pressure, or hypertension, during midlife are at a greater risk of developing dementia, irrespective of their blood pressure later on, a long-term follow-up study suggests.
The study, “Association of Midlife to Late-Life Blood Pressure Patterns With Incident Dementia,” was published in the Journal of the American Medical Association (JAMA).
Increasing evidence suggests that high blood pressure in middle age — from 45 to 65 years — may be a risk factor for cognitive decline and dementia.
However, several studies have pointed to a blood pressure decline in the years immediately before the onset of dementia. Additionally, the potential association between blood pressure patterns later in life — over 70 years — and cognitive function remains unclear.
To establish blood pressure recommendations for lowering the risk of dementia in older adults, researchers first need to understand the association between blood pressure patterns over time and cognitive function.
In this study, researchers evaluated the potential association of midlife to late-life blood pressure patterns with the occurrence of dementia and cognitive decline, using data from the Atherosclerosis Risk in Communities (ARIC) study.
The ARIC study, from the National Heart, Lung, and Blood Institute (NHLBI), enrolled nearly 16,000 adults from four U.S. communities. Scientists monitored the participants’ blood pressure over 24 years, including midlife to late-life. Participants were examined at the time of enrollment — between 1987 to 1989 — and followed-up over five visits until 2016 or 2017.
The U.S. communities included in the study were Washington County, Md.; Forsyth County, N.C.; Jackson, Miss.; and Minneapolis, Minn.
Researchers analyzed the data of 4,761 participants who underwent a detailed cognitive evaluation during visits five and six, in addition to having their blood pressure analyzed during the study period.
Participants were divided in five groups based on their blood pressure patterns over time: midlife and late-life normal blood pressure; midlife normal tension and late-life hypertension (greater than 140/90 mm Hg); midlife and late-life hypertension; midlife normal blood pressure and late-life hypotension, or abnormally low blood pressure (less than 90/60 mm Hg); and midlife hypertension and late-life hypotension.
Dementia and cognitive decline were assessed based on a battery of instruments, including the Functional Activities Questionnaire (FAQ), Clinical Dementia Rating (CDR), Ascertain Dementia-8 (AD8) informant questionnaires, Six-Item Screener telephone evaluations, and hospital data.
Among the participants, who ranged in age from 44 to 66, a total 2,821 (59%) were women and 979 (21%) were black. At the fifth visit, the participants’ mean age was 75 years — ranging from 66 to 90. A total 1,006 (21%) of them showed a mild cognitive deficit. Between visits five and six, 516 (11%) participants were found to have dementia.
The results showed that people with midlife and late-life hypertension, or midlife hypertension and late-life hypotension, were significantly more likely to develop dementia than those with normal blood pressure over time.
This highlighted the importance of hypertension during middle adulthood, which was supported by the additional observation that people with midlife hypertension were 41% more likely to develop dementia, irrespective of their late-life blood pressure.
Researchers hypothesize that chronic hypertension may impair the brain’s ability to maintain steady blood flow. That may lead to a reduction in brain blood flow, which is associated with brain damage.
Midlife hypertension followed by late-life hypotension also was more strongly associated with dementia among white people, and people under 74 years. Participants with this type of blood pressure pattern over time also were more likely to show mild cognitive decline later in life.
The data suggest that having significant blood pressure declines following hypertension may be more damaging at a younger age.
“However, given what is known about the gradual progression of neurodegenerative disease, the possibility that early neurological changes may be responsible for late-life declines in blood pressure cannot be ruled out,” the researchers said.
They also noted that their findings may have been influenced by the fact that participants who dropped out before visit five — and thus were not included in the final analysis — were more likely to have hypertension and poorer cognitive function during midlife.
The researchers also note that the results may not be generalized to the global population, since they were limited to participants from only four U.S. communities.
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