Seniors who are "housebound" seem to have nearly double the risk of developing Alzheimer's disease, a new study suggests.
The research doesn't prove that being confined to the house causes dementia, and other factors could explain the association. Still, the findings raise questions about the possible cost of isolation, said lead investigator Bryan D. James, a postdoctoral fellow at Rush Alzheimer's Disease Center in Chicago.
"People who don't leave their home as much aren't engaging with their environment and meeting new people," James said. "They may not be using their minds as much."
But James and his colleagues noted that underlying brain disease may also explain the results — that is, people may not be getting out as much because the insidious workings of Alzheimer's or another form of dementia may affect the way one moves through the world long before they affect memory or speech.
Alzheimer's disease afflicts an estimated 5.2 million people in the United States. That number is expected to grow to as many as 7.7 million Americans by 2030 as the Baby Boom generation ages.
The new study, published online April 15 in the American Journal of Geriatric Psychiatry, looks at something known as "life space."
"(Life space) is actually a measure that has come into vogue with gerontologists lately," James said. "Mostly it's been a measurement of mobility, figuring out whether people are getting around their environment, how much they're seeing that's different from their couch or bedroom or living room."
Researchers followed 1,294 seniors from two separate studies of older adults whose health was being tracked over time. At the beginning of this study, none of the elders showed signs of dementia. Over an average of 4.4 years, 180 developed Alzheimer's disease.
The researchers found that people who reported that they never left their home environment during a given week were about twice as likely to develop Alzheimer's disease in the five years of follow-up as those who traveled out of town. The research, James said, offers "a new way to see who's going to be more likely to develop dementia in the future."
The study also found that those who did not go beyond their driveway or front yard were also more likely to develop mild cognitive disorder, which can be an early manifestation of Alzheimer's.
There are some caveats to the research. Some of the participants lived in retirement homes and may have led full lives without needing to leave the buildings where they live; however, they were still counted as being housebound.
Still, the researchers found that the connection between isolation and Alzheimer's disease remained even when they adjusted their statistics so they wouldn't be thrown off by factors such as depression, social networks, disease and disability, as well as age, sex, education, race or preclinical dementia.
Why does all this matter? "People are interested in figuring out who's going to develop Alzheimer's and new ways to target more people likely to develop it," James said. "Maybe with the limited interventions we do have available, we can target them toward people who aren't leaving their homes."
Dr. James R. Burke, director of the Memory Disorders Clinic at Duke UniversityMedical Center, said isolation could offer a clue to possible dementia problems before they become obvious. "This will be particularly important when disease-modifying therapies are available, so that evaluations can be started and interventions considered before there are significant cognitive problems," Burke said.
"This paper is consistent with, but extends, previous findings that physical activity, intellectual engagement and social stimulation are important to delaying cognitive decline," Burke added.