Alzheimer’s disease, high blood pressure and heart disease are the three most common chronic conditions in assisted living facilities: 82 percent of residents have at least one of them, according to a new government study. But what is alarming is how these ailments overlap.

A Venn diagram based on data from the study, by the National Center for Health Statistics in 2010, shows just how often these three conditions coincide in patients, and why this overlap is becoming an important new field of study.

There are more than 733,000 people in American assisted living facilities. People move there when they, or their families, decide they need help with daily activities, like dressing, but don’t need the fuller medical services of a nursing home.

The study found that more than half the residents are 85 or older. Researchers were surprised that so many required medical care. “These findings suggest a vulnerable population with a high burden of functional and cognitive impairment,” the authors wrote in a data brief last year.

Forty-two percent of assisted living residents had dementia. About 9 percent had dementia, high blood pressure and some form of heart disease, like atherosclerosis.

Many studies have suggested a link between vascular disease and dementia, particularly Alzheimer’s, and researchers are focusing on possible interconnections. Dr. P. Murali Doraiswamy, a psychiatry professor at Duke, argues that it may not be possible to treat dementia without treating vascular problems.

But treating patients with multiple conditions can be very difficult. “We don’t universally do a great job of how we treat conditions that overlap, for example Alzheimer’s and high blood pressure,” said Dr. Cynthia Boyd, a professor of geriatric medicine at Johns Hopkins.

Diuretics to treat high blood pressure, for example, often increase the need to urinate, yet many patients with dementia are already incontinent. Some studies have suggested that on rare occasions statins used to lower cholesterol and prevent heart attacks may also have cognitive side effects, which could complicate care for dementia patients.

“Much of the way we practice medicine is looking at disease by disease,” Dr. Boyd said. “We aren’t doing enough thinking about how to add them together and really integrate care.”

The number of people with at least one of these three diseases is expected to continue to rise, increasing the need to focus on their overlaps. “It’s time for the best minds in vascular research to unite with the best minds in amyloid and tau protein research,” Dr. Doraiswamy wrote last year, referring to the proteins tied to Alzheimer’s disease. “Why don’t we start today?”