MONDAY, Aug. 24, 2009 (HealthDay News) -- High blood pressure is linked to loss of mental function in people over 45, a new study finds.
"A number of other studies have looked at the relationship between blood pressure and cognitive function," said George Howard, chairman of the department of biostatistics at the University of Alabama at Birmingham School of Public Health, and a member of the team reporting the finding in the Aug. 25 issue of Neurology. "Some studies found such a relationship, others did not. We think that this study, one of the larger ones and well done, adds substantially to whether there is a relationship here."
Specifically, the study found that every 10-point increase in diastolic blood pressure (the bottom number in the blood pressure reading), increased the odds of having some impairment in thinking ability by 7 percent.
It's not clear why diastolic pressure, taken while the heart is relaxing, should be associated with mental ability, Howard said.
"One idea is that diastolic pressure is tightly tied to small blood vessel disease and perfusion pressure," he said. Perfusion pressure is the force by which blood spreads through vessels of the brain. "Another idea is that people with high systolic pressure tend to die. Once they are dead, they cannot be part of our study."
That study is aimed at determining why blacks, and Southerners in general, are more likely to die of strokes than other Americans. The Reasons for Geographic and Racial Differences in Stroke Study has been following nearly 20,000 people 45 and older for years.
Data for the Neurology report was extracted from the overall study by Dr. Georgios Tsivgoulis, a neurologist who divides his time between the University of Alabama and Greece.
While the 7 percent increase in cognitive problems found in the study might seem small, "changing a modest amount can have a huge impact because of the large number of people involved," Howard said. Just under half of all of the study participants are taking medications to control high blood pressure.
"It's possible that by preventing or treating high blood pressure, we could potentially prevent cognitive impairment, which can be a precursor to dementia," Tsivgoulis said in a statement. But more research is needed to confirm that there is a relationship between high blood pressure and mental impairment, the statement said.
That thought was echoed in a statement by Dr. Walter J. Koroshetz, deputy director of the U.S. National Institute of Neurological Disorders and Stroke, which has supported the stroke study.
"The National Institutes of Health is now organizing a large clinical trial to evaluate whether aggressive blood pressure lowering can decrease a number of important health outcomes, including cognitive decline," the Koroshetz statement said.
Meanwhile, Howard said, the study shows one more reason why it is important to control high blood pressure.
The new study "supports a large body of literature that shows that hypertension, which almost always begins in mid-life, has an impact on cognition," said Dr. David Knopman, a professor of neurology at the Mayo Clinic in Rochester, Minn.
There are several reasons why some studies have not shown such an effect, Knopman said. "Some of the key differences reflect the age of the populations," he said. "If you have an older population, you have more people with hypotension, unusually low blood pressure, and the presence of them in the study wipes out the deleterious effects of hypertension. Also, the quality of care that the population has been receiving affects the results. If hypertension is treated effectively, you may not see an effect on cognition. It is difficult to know the quality of care in a study like this one."
The risks and treatment of high blood pressure are described by the U.S. National Library of Medicine.