Maine Perspective Front Page
Heart Disease Risk Factors Reduce Mental Abilities
Analyses of data based on two long-running studies of cardiovascular disease and mental abilities such as learning, thinking and reaction time, are providing powerful evidence that untreated high blood pressure and diabetes result in lowered cognitive ability.
A team of UMaine psychologists working with physicians and epidemiologists at the State University of New York Health Science Center at Syracuse and the Framingham Heart Study has documented an association between major risk factors for stroke and heart disease, and age-related decline in cognitive abilities, as measured by neuropsychological tests.
With data from two of the nation's longest-running studies of such risks, these investigators have obtained strong evidence for several important relationships:
- hypertension (high blood pressure) and diabetes are independently associated with an accelerated decline in cognitive functioning with advancing age
- untreated blood pressure levels in mid-life are associated with decline in cognitive ability many years later
- the risk of lowered cognitive functioning doubles in the presence of both hypertension and diabetes, and increases even further in the presence of smoking and obesity
Diabetes and hypertension are the key risk factors that drive these relationships.
"Prior to the Framingham study," says Merrill Elias, UMaine professor of psychology, "conventional wisdom said that high blood pressure might benefit sustained levels of cognitive functioning in old age because it maintained blood flow in the brain. People were operating on the idea that a rise in blood pressure was probably inevitable as you got older and might even be good for you. The idea is that it was essential for blood flow and brain oxygenation in old age. This is of course not true.
"Lowering blood pressure at all ages results in a dramatic decrease in prevalence and incidence of stroke. Now we know that these risk factors for stroke, hypertension and diabetes are associated with more rapid decline in cognitive ability over the life span. Further, we know that lowering of cognitive performance in hypertensive diabetics is probably exacerbated by obesity and cigarette smoking," says Elias.
UMaine scientists involved in the projects include Elias, also adjunct research professor of medicine and public health, Boston University; Michael Robbins, senior research associate and cooperating associate professor of psychology; and Penelope Elias, adjunct associate professor of psychology and senior research associate in mathematics and statistics, Boston University.
Longest-running UMaine study
Evidence that blood pressure is a predictor of cognitive ability has been accumulating for more than two decades through one of UMaine's longest-running research projects. Known as the Maine-Syracuse Studies of Hypertension and Cognitive Functioning, it has enrolled 2,000 men and women, ages 17-90 years old, from the Syracuse, N.Y., area and Maine. It has been supported by grants from the National Institute on Aging (NIA) of the National Institutes of Health (NIH).
The project was started in Syracuse in 1975 by Merrill Elias and David Streeten, professor of medicine. Michael Robbins and Penelope Elias joined the study in 1981. It has been funded every year since 1977, most recently with $311,177 from NIA in 1999. This work firmly established that high blood pressure is a risk factor for lowered cognitive ability.
In 1990, the research team decided to study additional cardiovascular/stroke risk factors in relation to cognitive ability. In 1991, with supplemental funding from the National Institute on Aging, the Maine research team obtained data from the Framingham Heart Study on a large sample of subjects who had never been treated for hypertension. The objective was to obtain more data on diabetes, obesity and cigarette smoking. They worked closely with Philip Wolf (neurology) and R.B. D'Agostino (epidemiology and biostatistics) at Boston University.
"Whether we use measures from the Framingham Study or the Maine-Syracuse study, we get the same result," says Elias. "Decline in cognition is strongest with high blood pressure and diabetes, and less strong with the other two factors."
About 85 percent of the Maine-Syracuse participants are from the Syracuse area. When they entered the study and again every five years, they received an extensive examination for hypertension and related risk factors (diabetes, obesity, smoking), and a battery of neuropsychological tests. Participants are being enrolled up to the present.
As a result, the Maine-Syracuse project has created one of the longest running and extensive data bases on blood pressure and comprehensive measures neuropsychological test performance in the world.
The Framingham Heart Study began in 1950 with a group of about 5,000 participants. Extensive medical data on cardiovascular risk factors have been obtained every two years. A battery of neuropsychological tests was first given to 1,799 of the subjects in 1968 and every two years since then.
Study results have been published in Hypertension, the American Journal of Epidemiology, Psychosomatic Medicine, Health Psychology, Journal of Gerontology and Psychology of Aging, and have been reported at professional meetings, including those of the American Heart Association.
"It appears that as the number of risk factors goes up, cognitive functioning goes down," Elias adds. "We must keep in mind, however, that effective treatment or prevention practices can delay or prevent accelerated cognitive decline associated with cardiovascular risk factors. Our data, and data from other investigators, should provide an additional incentive for people to control hypertension, diabetes, cigarette smoking and obesity through good health practices or medical treatment."
Decline is gradual
As demonstrated through neuropsychological tests, the decline in thinking abilities is gradual over time. "We are talking about hypertension and diabetes as insidious predictors of gradual and subtle decline in cognitive ability," Elias says. "Pathophysiological changes associated with hypertension and diabetes take many years. So do the cognitive changes associated with them."
As their sample population grows older, the Eliases, Robbins and their colleagues intend to pursue the relationship between reductions in cognitive functioning and the eventual onset of dementia and Alzheimer's Disease.
"It has been hypothesized, although it is yet unproven, that uncontrolled or poorly treated diabetes and hypertension may ultimately progress to dementia in some individuals, but not others. This may be the most exciting area of behavioral science research in the future. We hope that our data will encourage this line of investigation and that we can be part of this effort."
The team has already begun to extend collaborative work to include investigators at Oxford University, England, who are working on cardiovascular risk factors and dementia.