Saturday, October 23, 2010

High Blood Pressure as Risk Factor for Alzheimer’s

Having hypertension, or high blood pressure, reduces blood flow in the brains of adults with Alzheimer's disease, according to a study presented in 2007 at the annual meeting of the Radiological Society of North America.


"While hypertension is not a cause of Alzheimer's disease, our study shows that it is another hit on the brain that increases its vulnerability to the effects of the disease," said study co-author Cyrus Raji, scientist and M.D. and Ph.D. candidate at the University of Pittsburgh where the study was conducted.

Hypertension is a condition in which the blood circulates through the arteries with too much force. According to the National Heart, Lung and Blood Institute, approximately 50 million Americans have hypertension. People with hypertension are at elevated risk for heart attack, stroke and aneurysm. Recently, there has been mounting evidence tying cardiovascular health to brain health.

"This study demonstrates that good vascular health is also good for the brain," said co-author Oscar Lopez, M.D., professor of neurology and psychiatry at the University of Pittsburgh. "Even in people with Alzheimer's disease, it is important to detect and aggressively treat hypertension and also to focus on disease prevention."
For the study, the researchers used arterial spin-labeled magnetic resonance imaging (MRI), which can measure blood flow in the brain, to image 68 older adults. Arterial spin-labeled MRI is a novel, noninvasive technique that requires no external contrast agent.

The patient group included 48 normal individuals, including 38 with hypertension and 10 without; 20 Alzheimer's patients, including 10 with hypertension and 10 without; and 20 adults with mild cognitive impairment, 10 with hypertension and 10 without. Mild cognitive impairment, which affects brain functions such as language, attention and reasoning, is a transition stage between normal aging deficits in the brain and greater levels of dementia.

The MRI results showed that in all patient groups blood flow in the brain was substantially decreased in patients with hypertension compared to those without. Cerebral blood flow was lowest among the Alzheimer's patients with hypertension, but the normal group with hypertension showed significantly lower cerebral blood flow than the normal group without hypertension.

"These results suggest that by changing blood flow to the brain, hypertension--treated or untreated--may contribute to the pathology of Alzheimer's," Raji said.


Among the strongest new studies:
—MRI scans showed women 65 and older with high blood pressure had significantly more white matter lesions in their brains eight years later. The study included 1,403 women who were enrolled in a memory subset of the landmark Women's Health Initiative that tracked postmenopausal health. The worse their blood pressure, the higher volume of white matter damage, says the study published online last month in the Journal of Clinical Hypertension.

“This is a silent disease in the brain,” says lead researcher Dr. Lewis Kuller of the University of Pittsburgh. “It's evolving over time and it leads to very bad outcomes.”

—The journal Stroke just published similar evidence from a Johns Hopkins University-led study that tracked 983 people for more than 15 years, starting in middle age. The longer people spent with uncontrolled high blood pressure, the more white matter damage they accumulated. The researchers could see a change with each 20-point jump in too-high systolic pressure, the top number in a blood-pressure reading.

Clearly, hypertension alone doesn't doom someone to later dementia. Far more people, nearly one in three U.S. adults, have hypertension.

And there are plenty of other reasons to lower blood pressure: Hypertension is a leading cause of heart attacks, strokes and kidney failure.

But while some studies have found hypertension treatment lowered the dementia risk, others haven't.

Enter the NIH's SPRINT study, which has began in 2010, enrolling 7,500 hypertension patients age 55 and older around the country. The test: Whether aggressive treatment to lower systolic blood pressure below 120 — what's considered normal — will prove healthier than today's guidelines that urge getting it below 140, or 130 for diabetics.

The main focus is on heart and kidney health. But all participants will be screened for dementia, and a subset will undergo repeated cognitive testing and MRI scans to tell if lowering blood pressure also protects against a slide toward dementia. Another question: If older patients can tolerate bigger than usual blood pressure drops without side effects, such as falls.

With dementia rising fast as the population grays, even a small effect from better blood pressure control could have a big public health impact, says Dr. William Thies of the Alzheimer's Association.

Other dementia-preventing efforts, such as targeting the sticky amyloid plaques in Alzheimer's patients brains, haven't panned out so far — while hypertension control has little downside, notes Pittsburgh's Kuller.
“Until I can tell you how to get rid of amyloid in your brain, take care of the blood pressure.”


If the high blood pressure in general is more or less proven risk factor for Alzheimer Disease development indentified for the general population, it becomes even more significant when the elderly patients are subject of research. In the current study, researchers from the University of Western Ontario studied 990 older adults, most of whom were in their 80s. All had mild cognitive impairment, which causes problems in thinking and memory, and some had high blood pressure.

Some seniors with mild cognitive impairment have problems primarily with memory, and they are more likely to develop Alzheimer’s disease. Others, including those who suffer a stroke, are more likely to have problems with so-called executive function, which causes problems with making decisions and judgments.

The researchers looked at the seniors for five years. They found that Alzheimer’s disease and other forms of dementia developed in about 60 percent of those who had memory problems, regardless of whether they had high blood pressure or blood pressure that was under control.

But among those with thinking problems but no memory deficits, having high blood pressure was much more likely to lead to dementia. Almost 58 percent of those with thinking problems went on to develop dementia, compared to 28 percent of those whose blood pressure was under control.

High blood pressure is known to damage blood vessels throughout the body, including the brain. Therefore, keeping blood pressure in check may be important for maintaining brain health, especially when the brain may be under assault from other disease processes related to Alzheimer’s.

The researchers concluded that maintaining healthy blood pressure into old age may be critical for lowering the risk of developing Alzheimer’s disease. About a third of seniors with mild cognitive impairment have problems primarily with thinking. “Control of hypertension in this population could decrease by one-half the projected 50-percent five-year rate of progression to dementia,” the researchers concluded.

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