It is one of the greatest fears of growing old: losing your memory to Alzheimer's disease.
An estimated 4.5 million Americans have the disease and the number is growing. But who are those most at risk? Researchers are now discovering a direct link between Alzheimer's and heart disease.
This link between brain damage and heart damage was discovered during a series of autopsies more than 20 years ago.
While working in the Kentucky medical examiner's office, Larry Sparks was checking brain tissues looking for early signs of Alzheimer's disease.
He noticed that those who had the telltale plaques of Alzheimer's had one thing in common:
"I took the slides … and put them into two piles, those with heart disease and those without heart disease. And all the plaques and tangles showed up in the pile with heart disease," said Sparks, who is now a scientist with Sun Health Research Institute in Arizona.
That finding, for the first time, suggested heart disease could be a forerunner of brain disease.
"The link between heart disease and Alzheimer's disease is growing in strength every few months," said Bill Thies, the scientific director of the Alzheimer's Association. "And we predict it will continue to grow."
"I'm not surprised that there's a relationship," he said. "The heart is the organ that supplies essential elements to many parts of the body, and the brain is just one of the first."
A series of studies has revealed that the very same risk factors for heart disease also put people at greater risk of developing Alzheimer's.
In one study, people with high cholesterol in their 40s and 50s were three to five times more likely to become demented in their 60s and 70s.
"We found that excess cholesterol in the blood," Sparks told ABCNEWS, "leads to increased cholesterol in the brain and that increased production of cholesterol in the brain promotes production of plaques."
High blood pressure — above 140/90 — also increases the risk of Alzheimer's by damaging blood vessels.
"They become more stiff and this may lead to a decrease in the nutrients that can get to the brain and feed cells in the brain," said Lenore Launer, chief neuroepidemiologist at the National Institute on Aging.
Moderate smoking — 10 to 20 cigarettes a day — according to some research, can double or triple the chances of becoming demented.
"With every cigarette you smoke, there's probably an increased risk," Launer told ABCNEWS.
And preliminary Obesity research suggests the more overweight you are at 70 years of age, the greater your Alzheimer's risk.
The good news, researchers say, is that this is the first set of risk factors they've identified that people can actually do something about. Medications and lifestyle changes that have been used to promote heart health may actually protect brain health as well.