Midlife Hypertension Affects BP-Cognition Link in Old Age

June 05, 2014

Knowledge of blood pressure in midlife is crucial to understanding the link between blood pressure and cognitive impairment in old age, a new study suggests.

The study — part of the Age, Gene/Environment Susceptibility (AGES)-Reykjavik study, which has been following a population from Iceland since 1967 — found that the relationship between blood pressure and brain changes consistent with cognitive impairment in late life depended on whether the individual had a history of hypertension in midlife.

In those without a history of midlife hypertension, higher late-life systolic and diastolic blood pressure was associated with an increased risk for white matter lesions and cerebral microbleeds. In contrast, in participants with a history of midlife hypertension, lower late-life diastolic pressure was associated with smaller total brain and gray matter volumes and lower memory scores.

The researchers, led by Majon Muller, MD, PhD, from the National Institute on Aging in Bethesda, Maryland, report their results online June 4 in Neurology.

Previous Studies in Later Life Conflicting

Senior author Lenore J. Launer, PhD, also from the National Institute on Aging, explained to Medscape Medical News that previous studies have consistently reported an association between midlife hypertension and brain lesions, but studies on late-life blood pressure and brain outcomes have been inconsistent. Some studies have suggested that lower blood pressures in the elderly are linked to worse brain results.

"In a simple cross-sectional analysis, it may appear that high blood pressure is a good thing for the brain in the elderly, but we don't think this is actually the case. Sometimes lower diastolic pressures in the elderly can be caused by pathologic reasons — such as less elasticity in the blood vessels and lower weight due to illness/frailty, and it is not always a positive finding."

The researchers hypothesized that chronic hypertension since midlife leads to structural and functional cerebrovascular changes, disrupting vasoregulatory mechanisms, so that the normal association between blood pressure and markers of brain aging would be modulated.

For the current study, they analyzed data from 4057 older men and women without dementia participating in the AGES-Reykjavik study. Participants had blood pressure measurements from midlife (average age, 50 years) and measures of blood pressure, cognitive function, and brain structures on MRI in late life (average age, 76 years).

Dr. Launer commented: "Our results suggest that the midlife experience does influence what you see in later life. In people with no history of hypertension in midlife, raised blood pressure in late life is linked to harmful brain changes as we would expect.

"But in people who had hypertension at midlife, lower diastolic pressure in late life was associated with an increased risk of brain tissue loss in grey matter consistent with cognitive problems, such as lower memory scores," she said. "What we think we're seeing here is that earlier hypertension has already done some damage to blood vessels so the diastolic pressures can be lower. It is actually a sign of pathology rather than good health."

Lifelong Blood Pressure Control Important

"Our take-home message is that people need to control their blood pressure all through their lives to lower their risk of brain atrophy and small vessel disease in later life," Dr. Launer said.

"And when interpreting late-life blood pressure/dementia associations, it is important to know blood pressure history and other pathology. It is definitely not the case that increased blood pressure is good for you in old age," she added.

Dr. Launer pointed out that this study combines both sides of the blood pressure/dementia story. "By including midlife blood pressure history we can identify individuals who may show this altered pathological blood pressure response in later life. We have shown that if blood pressure was not controlled in midlife, the future trajectory for blood pressure is different."

The researchers conclude that future studies should aim to better define patients who may be at higher risk for cerebral complications of lower blood pressure and to understand more about the mechanism.

The study was supported by a grant from the National Institutes of Health, the Hjartavernd (the Icelandic Heart Association), the Althingi (the Icelandic Parliament), and Alzheimer Nederland. The authors have disclosed no relevant financial relationships.

Neurology. 2014;82:2187-2195. Abstract

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