Researchers focused on the effects of emotional isolation, or loneliness, in which people perceive themselves as feeling socially isolated and disconnected from others -- sometimes even if they're surrounded by family and friends.
"It turns out people who have this feeling of being socially isolated are at higher risk of developing Alzheimer's," says David A. Bennett, MD, co-author of the study and director of the Rush University Medical Center Alzheimer's Disease Center in Chicago.
Though a small social network of friends and family has been linked in previous research to a higher risk of Alzheimer's, Bennett's group focused on a person's perception of being alone, regardless of their social network size.
"We are talking about a tendency to feel isolated and alone in the world," he says. "You can have a small network and not feel isolated; or you can have a large network but don't know how to connect, and feel isolated."
Bennett and his colleagues recruited 823 people (average age: nearly 81) in and near Chicago. All were free of dementia at the start of the study.
Participants had agreed to donate their brains at death to the Rush Memory and Aging Project.
The researchers assessed loneliness using a five-item questionnaire in which participants agreed or disagreed with statements that they didn't have enough friends, often felt abandoned, or experienced a sense of emptiness. They repeated the test annually.
A score of 5 indicated the most loneliness. At the start, the participants' average score was 2.3.
76 Developed Alzheimer's
During the follow-up of nearly four years, 76 participants developed Alzheimer's.
When the researchers looked at the scores of those with Alzheimer's, they found risk of the disease was more than double for those who had loneliness scores of 3.2 (landing them in the bottom 90th percentile) compared with those who were not lonely and had an average score of 1.4 (in the top 10th percentile).
The link between loneliness and Alzheimer's was there, Bennett says, even when they adjusted for small social network and infrequent socializing, both known risk factors.
However, when they autopsied the brains of 90 people who died during the study, they didn't find a link between high loneliness scores and the physical brain changes that point to the disease.
Though loneliness increased the chances of getting a clinical diagnosis of Alzheimer's, it didn't seem to increase the physical brain changes tied to the disease and seen at autopsy.
More research is needed to figure out exactly how loneliness boosts the risk of Alzheimer's, Bennett says.
"The loneliness is doing something to the brain," he says. It may be that it lowers your brain reserve, setting you up for memory problems.
Several previous studies have found a link between social isolation, mental decline, and a higher risk of dementia, Bennett notes.
Social isolation is often brought on, he says, by being single, participating in few activities with others, or having few people in your social network.
If you have seven people in your social network (defined as people other than your spouse whom you feel close to and can confide in), you are about average, Bennett says.
"People with 2, 3, or 4 are at greater risk [of dementia] compared to people with 12 or 13," he says, citing other research.
Other studies have showed that people who tend to be depressed and who tend to feel overwhelmed with stress are also at greater risk for Alzheimer's, he says.
For now, Bennett says, "People should be aware that negative emotions in the form of depression, loneliness, and being overwhelmed are bad for the brain."
Other Experts Weigh In
The stdy may affect how doctors assess older patients and their dementia risk, says Helena Chui, MD, a neurologist and director of the Alzheimer's Disease Research Center at the University of Southern California Keck School of Medicine, Los Angeles.
"I'm going to ask more about 'Do you feel lonely?'" she says, after reading the study results.
It may be easier for patients to admit loneliness, she suspects, than depression or other problems.
"It's a relatively new concept," says Bill Thies, PhD, vice president for medical and scientific relations for the Alzheimer's Association, based in Chicago. Whether the finding will be clinically useful remains to be proven, he says.
The study is published in the February 2007 issue of the Archives of General Psychiatry.
SOURCES: David A. Bennett, MD, neurologist; director, Rush University Alzheimer's Disease Center, Chicago. Wilson, R. Archives of General Psychiatry, February 2007; vol 64: pp 234-240. Helena Chui, MD, professor and chairman of neurology and director of the Alzheimer's Disease Research Center, University of Southern California Keck School of Medicine, Los Angeles. Bill Thies, PhD, vice-president for medical and scientific relations for the Alzheimer's Association, Chicago.
By Kathleen Doheny
Reviewed by Louise Chang