A research team from Karolinska Institutet in Stockholm led by professor Laura Fratiglioni, M.D., Ph. D., found that a substantial drop in systolic blood pressure (the higher number in a blood pressure reading) predicted the onset of dementia in people with a systolic pressure of less than 160 millimeters of mercury (mm Hg). A drop in systolic pressure of 15 mm Hg or more was linked to a three-fold increase in the risk of getting Alzheimer's disease or other dementia.
The same 15 mm Hg or more decrease in patients who already had vascular disorders such as stroke and diabetes mellitus increased their risk of Alzheimer's 2.4 times, and 2.5 times for all types of dementia.
"Our findings imply that poor blood flow in the brain, resulting from an extensive decline in blood pressure, may promote the dementia process," said lead author Chengxuan Qiu, M.D., a postdoctoral epidemiologist at the Karolinska Institutet.
However, because so few studies have addressed the connection between blood pressure decline and dementia, these findings need further verification. "Indeed, we have to consider that patients with dementia experience a decline in blood pressure some years before diagnosis, which continues to decline after the onset of dementia," Fratiglioni said.
Alzheimer's disease is the most common cause of dementia in Western countries. Other causes include repeated strokes and secondary dementia resulting from neurological disorders such as Parkinson's disease.
Previous studies have shown that high blood pressure in midlife is associated with an increased risk of dementia and Alzheimer's disease later in life. However, studies investigating the link between dementia and blood pressure in late life have been conflicting. In a previous study, the Karolinska researchers suggested that both high and low blood pressure may damage cognitive abilities in the elderly.
This study aimed to verify blood pressure variations before and after dementia diagnosis, and to investigate whether blood pressure decline was predictive of Alzheimer's disease and dementia.
Researchers examined 947 people age 75 or older who had no evidence of dementia when they entered a large study of aging and dementia conducted in the Kungsholmen district of Stockholm. Each participant had blood pressure measurements taken and physical examination done when they began the study and again three and six years later.
Of these enrollees, 147 were diagnosed with Alzheimer's disease and 39 with other dementia at the three-year follow-up examination. At six years, researchers diagnosed another 91 with Alzheimer's and an additional 27 with other types of dementia.
"Our data show no substantial differences in blood pressure levels at enrollment between non-demented persons and those that were demented three to six years later," said co-author Bengt Winblad, M.D., Ph.D., professor of geriatric medicine at Karolinska Institutet and the principle investigator of the Kungsholmen project. "However, some elderly people who experience a significant decline in systolic blood pressure three to six years before diagnosis do have an increased risk of dementia and Alzheimer's disease."
"These findings indicate a possible threshold level in systolic pressure, especially for people with vascular disease in whom further reduction of blood pressure under this level may precipitate dementia onset," Qiu said. "Using antihypertensive medications is important for high blood pressure and related disorders, but our findings suggest that it is necessary to monitor these drugs in the very old to avoid a probable dangerous drop of blood pressure under a certain threshold."
American Heart Association spokesperson Daniel Jones, M.D. cautioned that the study doesn't mean high blood pressure in the elderly should be untreated.
"The results of this study are of interest to the research community as we attempt to understand the complex relationship between blood pressure and dementia," Jones said. "However, data from well-conducted randomized clinical trials have consistently supported the view that treating systolic blood pressure to 140 mm Hg or less in the elderly is beneficial. No clinical trial data to date has indicated any adverse impact on cognitive function. Indeed, there is strong data from some studies that support the idea that lowering blood pressure prevents dementia."
The study did not specifically address how blood pressure might be related to the onset of dementia. However, the research team said scientific evidence indicates that high blood pressure is a risk factor for dementia and Alzheimer's disease, but continual or episodic low blood pressure may also increase the dementia risk by reducing blood flow to the brain.
It is possible that subtle degeneration of cells in the blood-pressure-regulating centers of the brain – the sort of damage that elsewhere in the brain leads to dementia – may cause the pressure to fall. An extensive decline in blood pressure, in turn, may lead to a reduced blood flow in brain, which accelerates further the processes of dementia.
"Therefore, blood pressure decline can be considered an accelerating factor of clinical dementia and Alzheimer's disease, rather than an initiator of the dementing process," the authors said.
Other co-authors are Eva von Strauss, Ph.D. Editor's note: For more on stroke, visit the American Stroke Association Web site: strokeassociation.org.
NR04-1284 (Stroke/Qiu)
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