AGING
June 27, 2014

Low Blood Pressure and Cognitive Decline

High blood pressure in old age may not be all bad: It can mean more blood to the brain.

When it comes to treating high blood pressure, one size may not fit all. Blood pressure goals in some older adults may need to be left higher than in in others, based on their past blood pressure history, according to a recent study which looked at blood pressure in midlife and old age.

The study examined how blood pressure control affected changes in brain structure and cognitive function. Many researchers have shown that lowering blood pressure in old age decreases the risk of cardiovascular disease such as strokes, but this doesn't always have such a positive impact on preserving thinking and reasoning skills in seniors.

In some older people, lower blood pressure may actually be detrimental to brain function.

It appears that some tweaking of these guidelines may be needed to take these findings into account. People with higher blood pressure during middle age are at increased risk for cognitive impairment later on, but as they grow older, this risk changes. In some older seniors, lower blood pressure may diminish brain function.

Researchers wondered why these differences were observed and suspected that the answer involved whether or not the patient had had hypertension in midlife.

Roughly four thousand Icelandic men and women were assesed at midlife (50 +/- six years) and later life (76+/- five years). Brain structure was viewed using an MRI; cognitive function was measured with standardized testing; and blood pressures were recorded at both time periods.

Elevated blood pressure (BP) was defined as greater than 140/90. The participants also filled out questionnaires about other health and life style issues.

Having higher late life blood pressures, both Systolic pressure and Diastolic pressure, were associated with an increased risk of white matter lesions and with small bleeds. This finding was most pronounced among patients who did not have a history of midlife hypertension.

If blood pressure is too low in old age, the brain may no longer have the ability to compensate and increase the flow to vital brain tissue; and areas of the brain will not receive adequate blood and oxygen and will become atrophied.

When participants had a history of midlife hypertension, lower late life blood pressure was associated with smaller total brain size and with decreased volumes of grey matter. These same patients also had lower memory score and tests of cognitive function.

The researchers concluded that the effects of blood pressure late in life on both brain structure, as well as thinking and reasoning functions, differed depending on the history of blood pressure in midlife. There is a cumulative effect of early high blood pressure and late low blood pressure that makes certain patients susceptible to brain atrophy and cognitive impairment.

The researchers suggest that when a person has high blood pressure in midlife, the brain’s structure and regulatory mechanisms can both be altered. This could leave the brain tissue unable to protect itself against the potentially harmful effects of lower blood pressure.

If blood pressure is too low in old age, the brain may no longer have the ability to compensate and increase the flow to vital brain tissue. Areas of the brain will not receive adequate blood and oxygen and will become atrophied. This would explain the loss of both tissue and cognitive function observed in some elders.

Another possible explanation is that low diastolic blood pressure in older patients could be part of a larger package of cardiovascular and organ disease including coronary artery disease, heart failure, and increased arterial stiffness. The atrophy and loss of brain volume issues, researchers say, could be part of a larger health phenomenon rather than the effect of a single circulation-related problem.

This National Institute of Aging study has potentially important implications for the management of high blood pressure in the older population. The researchers recommend that healthcare providers consider the patient’s midlife history of blood pressure when prescribing blood pressure treatment in older age individuals.

Less strict blood pressure control goals may be appropriate to avoid atrophy and volume loss in some patients with elevated blood pressure, they suggest. Conversely, in patients without a history of midlife hypertension who develop high blood pressure in old age, the increased risk of bleeding must be considered when planning treatment. The researchers do not recommend discontinuing treatment of abnormal blood pressure in midlife or in old age.

Elevated blood pressure causes a number of health problems throughout the body including the brain, heart, kidneys, blood vessels, and eyes. The impact of uncontrolled blood pressure is cumulative. High blood pressure should never be ignored but rather should be investigated to find out whether there is an underlying cause that requires attention.

Most high blood pressure has no identifiable cause and is called essential or primary. Regardless of the type, hypertension requires monitoring and many people, in addition to lifestyle, exercise, weight, and dietary modifications, benefit from medication treatment.

Patients should seek their physician’s guidance if they have concerns about their blood pressure readings or medication side effects. Having your health history available, including past blood pressure measurements or records of treatment, can help your doctor make informed treatment recommendations.

The study is published in Neurology

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