For most people, systolic blood pressure (the top number in a reading) around 120 is a healthy goal. In fact, a recent study published in the New England Journal of Medicine found that it cuts the risk of heart attack, heart failure, stroke, and death by about 25 percent compared with the currently recommended target pressures of 140 and 150 for people under and over age 60, respectively. (For more information about the study, read 6 Questions About Blood Pressure.)

But it turns out that for elderly people at risk for dementia, the new blood pressure targets may be too low, putting them in danger of more rapid cognitive decline.

In a study published in JAMA Internal Medicine last April, researchers from the University of Florence in Italy found that in a group of 172 older adults with an average age of 79, of whom most had either dementia or mild cognitive impairment, those with the lowest daytime systolic blood pressure—128 or less—had the greatest decline in performance on standard mental function tests. They also found that those who lowered their blood pressure with medications experienced more mental decline.

Rusty Pipes

"When you have high blood pressure and elevated cholesterol in midlife, that tends to be associated with more dementia as you get older," says Paul Rosenberg, MD, associate director of the Memory and Alzheimer's Treatment Center at Johns Hopkins School of Medicine in Baltimore. "But at a certain age, the switch seems to flip for some of these vascular risk factors. In general, tight control of blood pressure is probably not a good idea for older people at risk of dementia." It's also possible that lowering blood pressure excessively with medication can have a negative impact on cognition, he says.

What's going on here? How can lower blood pressure be good for you when you're 55 and bad for you when you're 80?

Think of the heart as a pump and the vessels as a system of pipes, says Behnam Sabayan, MD, PhD, a postdoctoral research fellow at Leiden University in the Netherlands specializing in cardiovascular and hemodynamic factors in brain aging, who published a commentary on blood pressure and cognitive impairment that accompanied the Italian study. "In relatively younger people, high blood pressure damages the pipes, the conduits to the pump," he says. "But when the pump doesn't work properly in advancing age and the pipes are a bit rusty, maybe slightly higher pressure is needed to bring blood to the end organs—including the brain."

Tips to Stay Safe

In the absence of blood pressure guidelines that specifically address older adults with cognitive impairment or dementia, stroke and aging specialists suggest the following:

• Don't stop any blood pressure medications without first talking with your physician.
• Share with your physician your unique circumstances, including coexisting conditions such as diabetes or kidney disease, family history, and other risk factors for both cardiovascular disease and dementia.
• Be sure to report to your health care provider any dizziness, falls, difficulty walking, or other unusual impairments that may suggest low blood pressure.