Social Buffer Against Alzheimer’s?

April 25, 2006 -- Elders who spend time with friends and family may get some shelter from Alzheimer's disease, according to a study in The Lancet Neurology.

David Bennett, MD, and colleagues studied 89 elders who are part of the larger Rush Memory and Aging Project. The project is based at Chicago's Rush University Medical Center, where Bennett works.

Participants were in their early 80s, on average, and didn't have dementia when they joined the study. Alzheimer's is the most common type of dementia in older adults.

Every year until death, participants were screened for Alzheimer's and took 21 tests of mental skills (including memory and reading). They also agreed to let their brains be examined after death for the project.

Friends and Family

Participants reported how many close friends and family members (not just their spouse and children) they saw every month.

The researchers focused on people that participants felt at ease with and could talk to about private matters or ask for help. "Social network size was the number of these individuals seen at least once per month," Bennett and colleagues write.

After participants died, brain autopsies were done to check the amount of plaque and tangles -- which have been linked to Alzheimer's -- in participants' brains. The researchers found varying degrees of brain plaque and tangles.

Higher Mental Test Scores

Participants with larger social networks tended to have scored higher on their mental tests, even if they were later found to have more severe amounts of brain plaque and tangles. In other words, a participant that would have been expected to have more severe Alzheimer's based on their brain analysis, didn't when they had a large social network.

"These results were unchanged after controlling for cognitive, physical, and social activities, depressive symptoms, or number of chronic diseases," the researchers write.

Large social networks were especially linked to scores on working memory and semantic memory. Semantic memory includes participants' knowledge about the world; it's also involved in mental skills such as language.

Study's Limits

The study doesn't prove that large social networks buffer against Alzheimer's disease. Possibly, having a large social network reflects other traits that are helpful against Alzheimer's.

The study also doesn't blame Alzheimer's disease on sparse social networks.

Exactly how social networks might affect Alzheimer's disease isn't clear. Bennett's team suggests two ideas:

• Mental traits that let people build and keep large social networks might be a brain reserve against cognitive impairment, despite Alzheimer's brain symptoms.
• Mental traits linked to large social networks may make up for the effects of other degenerating mental systems.

Bennett's team adjusted for many factors related to Alzheimer's disease, but they couldn't control for all possible influences. For instance, the researchers note that they didn't examine the quality of participants' social networks or participants' social networks early in life.