Hypertension in Elderly Appears to Cause Mild Cognitive Impairment that Leads to Alzheimer's

How high blood pressure increases the risk of cognitive impairment or dementia in senior citizens is not unclear

Dec. 10, 2007 – Researchers just cannot seem to find enough bad to say about high blood pressure. A new study being released tomorrow finds that hypertension in senior citizens – people age 65 and older - can lead to mild cognitive impairment, a condition that involves difficulties with thinking and learning.

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“Mild cognitive impairment has attracted increasing interest during the past years, particularly as a means of identifying the early stages of Alzheimer’s disease as a target for treatment and prevention,” the authors write as background information in the article. The report is in the December issue of Archives of Neurology, one of the JAMA/Archives journals.

About 10 out of every 1,000 elderly American without dementia will develop mild cognitive impairment each year, the article reports. And, about 10 to 12 percent of these will progress to Alzheimer's disease. Of the elderly without mild cognitive impairment, only about 1 to 2 percent will develop Alzheimer's.

Christiane Reitz, M.D., Ph.D., and colleagues at the Columbia University Medical Center, New York, followed 918 Medicare recipients age 65 and older (average age 76.3) without mild cognitive impairment beginning in 1992 through 1994.

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All participants underwent an initial interview and physical examination, along with tests of cognitive function, and then were examined again approximately every 18 months for an average of 4.7 years.

Individuals with mild cognitive impairment had low cognitive scores and a memory complaint, but could still perform daily activities and did not receive a dementia diagnosis.

Over the follow-up period, 334 individuals developed mild cognitive impairment.

This included 160 cases of amnestic (associated with amnesia) mild cognitive impairment, which involves low scores on memory portions of the neuropsychological tests, and 174 cases of non-amnestic mild cognitive impairment.

Hypertension (high blood pressure) was associated with an increased risk of all types of mild cognitive impairment that was mostly driven by an increased risk of non-amnestic mild cognitive impairment.

Hypertension was not, however, associated with amnestic mild cognitive impairment, nor with the change over time in memory and language abilities.

“The mechanisms by which blood pressure affects the risk of cognitive impairment or dementia remain unclear,” the authors write.

“Hypertension may cause cognitive impairment through cerebrovascular disease. Hypertension is a risk factor for subcortical white matter lesions found commonly in Alzheimer’s disease.

"Hypertension may also contribute to a blood-brain barrier dysfunction, which has been suggested to be involved in the cause of Alzheimer’s disease."

Other possible explanations for the association are shared risk factors, including the formation of cell-damaging compounds known as free radicals.

“Our findings support the hypothesis that hypertension increases the risk of incident mild cognitive impairment, especially non-amnestic mild cognitive impairment,” the authors conclude.

 “Preventing and treating hypertension may have an important impact in lowering the risk of cognitive impairment.”

Editor's Note: This study was supported by grants from the National Institutes of Health; the Charles S. Robertson Memorial Gift for Research in Alzheimer’s Disease; and the Blanchette Hooker Rockefeller Foundation.