December 23, 2007
People with high blood pressure appear to be at elevated risk for mild cognitive impairment, a condition marked by forgetfulness and memory loss. In many people, mild cognitive impairment is a harbinger of the more serious thinking and memory problems of full-blown Alzheimer's disease. The findings appeared in the December issue of the Archives of Neurology, a medical journal from the American Medical Association.
"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 of the study wrote. Nearly one in every 100 elderly people who are free from dementia develops mild cognitive impairment each year. Of those, 10 percent to 12 percent progress to Alzheimer's disease each year, compared with 1 percent to 2 percent in the healthy elderly population.
Researchers at Columbia University Medical Center in New York studied 918 Medicare recipients age 65 and older; their average age was 76. All were mentally alert and free from memory problems when they first enrolled in the study, from 1992 to 1994.
All participants underwent an initial interview and physical examination, along with tests of cognitive function. They were then examined again every 18 months for the next four or five years.
During that time, more than a third of the men and women in the study developed mild cognitive impairment. They scored low on memory tests, but could still perform daily activities and live independently. None received a diagnosis of Alzheimer's or other forms of dementia.
About half, or 160, of the participants who developed mild cognitive impairment were diagnosed with what's known as "amnestic" mild cognitive impairment. The condition is marked mainly by memory problems. Another half, or 174, had what's called "non-amnestic" mild cognitive impairment, which primarily affects functions other than memory. Cognitive aspects such as language skills and attention span may be more or less affected by either form of the condition.
High blood pressure was associated with an increased risk of mild cognitive impairment, but was particularly linked to the non-amnestic form of mild cognitive impairment. Elevated blood pressure was not specifically 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 affect the brain because of damage to the blood vessels that nourish the organ, the researchers speculate. Damage to the subcortical white matter of the brain has been detected in people with high blood pressure.
The condition has also been associated with problems in the blood-brain barrier, which separates the brain from other portions of the body, and with an excess of cell-damaging compounds called free radicals. All these factors may play a role in the onset of mild cognitive impairment and later, Alzheimer's disease, in those with high blood pressure.
"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." Non-amestic MCI, however, is thought to be less likely to progress to Alzheimer's than amnestic MCI.
Studies on the impact of blood pressure and Alzheimer's disease have been mixed. Some studies have found that high blood pressure often precedes Alzheimer's and other forms of dementia, while other studies have not found links between the two. Other studies have reported a link between low blood pressure and Alzheimer's disease. Some research suggests that controlling blood pressure through blood pressure drugs may also help to slow the decline of Alzheimer's disease. [See the article, "Blood Pressure Drugs May Slow Mental Decline of Alzheimer's."]
As scientists continue to unravel the links between high blood pressure and Alzheimer's disease, experts generally agree that a heart-healthy lifestyle may help to keep the brain young. Heart-healthy activities include regular exercise and an antioxidant diet rich in fresh fruits and vegetables and low in artery-clogging saturated fats. What's good for the heart is good the brain, a growing body of evidence suggests. That includes keeping blood pressure in a healthy range.
Christiane Reitz, MD, PhD; Ming-Xin Tung, PhD; Jennifer Manly, PhD; et al: "Hypertension and the Risk of Mild Cognitive Impairment." Archives of Neurology, Volume 64, Number 12, December 2007, pages 1734-1740.