MAINE home

Research Grants

News Releases Public Affairs

Calendar of Events

Department Directory

UMaine Today Research Archives

UMaine Today Research by e-mail Send message: "subscribe UMaine Today Research (your name)" Leave subject line blank.

Off Campus Links

Maine Science and Technology Fdn. for Maine research

ScienceDaily

SciNews/MedNews

Eurekalert

Humboldt Field Research Institute

Posted December 23, 1999

Risks for Stroke and Heart Disease 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 University of Maine 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:

1) hypertension (high blood pressure) and diabetes are independently associated with an accelerated decline in cognitive functioning with advancing age;

2) untreated blood pressure levels in mid-life are associated with decline in cognitive ability many years later;

3) 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 rise in blood pressure was probably inevitable as you get older and might even be good for you. That is where the phrase `essential hypertension' comes from. The idea is that it was essential for blood flow and brain oxygenation in old age. This is of course not true. Lowering of 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, who is also an adjunct research professor of medicine and public health at Boston University; Michael A. Robbins, senior research associate and cooperating associate professor of psychology; and Penelope K. Elias, adjunct associate professor of psychology at UMaine and senior research associate in mathematics and statistics at Boston University.

Longest running UMaine study

The 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 ranging from 17 to 90 years old from the Syracuse, New York 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 H. P. Streeten, professor of medicine. Michael Robbins and Penelope K. 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. Thus in 1991 with supplemental funding from the National Institute on Aging, the Maine research team obtained data 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 A. 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. Nevertheless, the relationship still holds."

About 85% of the Maine-Syracuse participants are from the Syracuse, New York 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.

Studies vary in cognitive tests

The two studies also vary in their approaches to cognitive function. The Framingham study uses a short battery of neuropsychological tests emphasizing memory. The Maine-Syracuse study uses a more comprehensive battery measuring speed of performance, memory, fluid intelligence, and crystallized-verbal ability. However, the Framingham Study has much more data on a wide range of cardiovascular disease risk factors and diseases than does the Maine-Syracuse Study.

Study results have been published in Hypertension, the American Journal of Epidemiology, Psychosomatic Medicine, Health Psychology, the Journal of Gerontology, the 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.”

In the Maine-Syracuse project, researchers asked participants to recall diverse materials presented to them, ranging from strings of numbers to short stories to complex figures. Various other tests required solving arithmetic problems, providing definitions for words, listing as many words as possible starting with a specific letter, identifying some likeness between apparently dissimilar objects, producing designs, and performing motor tasks with and without visual reference.

Decline is gradual

As demonstrated through these neuropsychological tests, the decline in thinking abilities is gradual over time. "We are not talking about people who are cognitively impaired or demented," says Elias. "We are talking about hypertension and diabetes as insidious predictors of gradual and subtle decline in cognitive ability. Pathophysiological changes associated with hypertension and diabetes take many years. So do the cognitive changes associated with them. Taken from the perspective of the individual, the individual with untreated or poorly controlled hypertension, particularly in the presence of diabetes, obesity, and smoking, may decline more in cognitive ability over time than they would if they were free from risk factors.”

The team of researchers controlled statistically for factors such as age, sex and medication to minimize the chances that the analysis could reflect differences in those areas. They also eliminated from the study people who had suffered a heart attack, stroke, brain trauma, psychiatric illness or dementia.

“The mechanisms for change in the brain that would affect cognitive functioning should be the same for both diabetes and high blood pressure,” Elias adds. “With untreated hypertension, you have gradual destruction of the arterial wall, changes in autoregulation, altered oxygen flow to the brain, and in old age, lesions in the white matter of the brain and small areas of dead brain tissue (infarctions) from lack of oxygen perfusion. Pathophysiological changes in the brain associated with diabetes are similar, and thus, you would expect both to exert a negative impact on cognitive ability, and they do.

“Similarly cigarette smoking ultimately results in decreased or intermittent changes in brain oxygenation and damage of the epithelial walls of the arteries. Obesity contributes to these effects by increasing the risk of diabetes and hypertension,” says Elias.

Association with dementia?

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. “We know from the work of others that diabetes, hypertension, and lowered cognitive functioning at a younger age are risk factors for dementia, including probable Alzheimer's Disease, in old age,” says Elias.

“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.

Return UMaine Today Research home