People suffering from cardiovascular disease who have lower-than-normal blood pressure may face a higher risk of brain atrophy -- the death of brain cells or connections between brain cells, Dutch researchers report.
Such brain atrophy can lead to Alzheimer's disease or dementia in these patients. In contrast, similar patients with high blood pressure can slow brain atrophy by lowering their blood pressure, the researchers added.
Blood pressure is measured using two readings. The top number, called systolic pressure, gauges the pressure of blood moving through arteries. The bottom number, called diastolic pressure, measures the pressure in the arteries between heartbeats. Normal blood pressure for adults is less than 120/80, according to the U.S. National Heart, Lung, and Blood Institute.
For the study, 70 to 90 was considered normal diastolic blood pressure, while under 70 was considered low.
"Our data might suggest that patients with cardiovascular disease represent a subgroup within the general population in whom low diastolic blood pressure might be harmful," said researcher Dr. Majon Muller, an epidemiologist and geriatrician at VU University Medical Center in Amsterdam.
On the other hand, lowering blood pressure in people with high blood pressure might slow brain atrophy, she said.
"Our findings could imply that blood pressure lowering is beneficial in patients with higher blood pressure levels, but one should be cautious with further blood pressure lowering in patients who already have low diastolic blood pressure," Muller added.
The report was published in the June 10 online edition of JAMA Neurology.
A U.S. expert noted the complex effects of blood pressure levels on the brain.
"High blood pressure has been shown to increase the risk of vascular brain lesions and brain atrophy. Trials of blood pressure lowering in patients with hypertension have shown reduced risk of brain lesions," said Dr. Gregg Fonarow, a professor of cardiology at the University of California, Los Angeles, and a spokesman for the American Heart Association.
However, in patients with hypertension, the relationship between the levels of systolic and diastolic blood pressure and brain atrophy has been less clear, he said.
This new study suggests that low diastolic blood pressure levels were associated with brain atrophy regardless of blood pressure levels after patients developed dementia, Fonarow said.
"These findings suggest that while treatment and control of high blood pressure is very important for brain and cardiovascular health, caution is needed in patients who have low diastolic blood pressure levels," he said.
To see what changes blood pressure would make in the progression of brain atrophy, Muller's group studied 663 patients who suffered from heart disease, cardiovascular disease, peripheral artery disease or abdominal aortic aneurysm. The average age of participants was 57 and most were men.
People whose diastolic blood pressure was below 70 had more brain atrophy over time, the study found. For people with higher-than-normal blood pressure, brain atrophy decreased when their blood pressure did. When blood pressure rose, however, atrophy increased.
Another expert, Dr. Sam Gandy, associate director of the Mount Sinai Alzheimer's Disease Research Center in New York City, said that the finding "is an important cautionary tale."
"This implies that one must adapt the approach to the individual patient. Correction of hypertension is helpful, but reducing blood pressure in patients with normal blood pressure is risky and complicated," Gandy said.
Although the study found an association between low diastolic blood pressure and the risk of developing brain atrophy for people with artery disease, it did not establish a cause-and-effect relationship.