Background: Social isolation has been correlated with an increased risk of dementia and cognitive decline. This social isolation includes being unmarried, having a small social network, and participating in few activities with others. Social isolation, however, differs from loneliness, which is when persons have access to social support but are dissatisfied with their interactions. Although social isolation has been shown to increase the risk of dementia, a study comparing loneliness with dementia had inconsistent findings. Wilson and colleagues evaluated the effect that loneliness has on the risk of developing Alzheimer's disease. They also assessed depressive symptoms and social isolation; the relationship of loneliness to change in cognition; and the relationship between loneliness and the neuropathologic lesions found in patients with Alzheimer's disease.

The Study: Participants in the study were older patients (mean age, 80.7 years) who had no evidence of dementia at baseline. They also agreed to an annual in-home evaluation and brain donation after death. The evaluation included a structured medical history and complete neurologic and cognitive testing that used the National Institute of Neurological and Communicative Disorders and Stroke–Alzheimer Disease and Related Disorders Association criteria. Loneliness was assessed by a five-item questionnaire modified from an established loneliness scale. Additionally, social isolation was evaluated by using two measures of social function. Neuropathologic evidence of Alzheimer's disease was evaluated during a uniform postmortem examination of multiple brain regions.

Results: Of the 823 participants, 75.7 percent were women. During the study, 76 participants developed Alzheimer's disease, and 90 died. The risk of Alzheimer's disease was more than double in participants who had high scores on the loneliness scale compared with those who had low scores on the same scale. Controlling for social isolation in the data analysis did not change this relationship. Loneliness also was associated with lower levels of cognitive function at baseline and accounted for a more rapid decline over time. In those who died during the study, there was no correlation between scores on the loneliness scale and postmortem examinations showing Alzheimer's disease or cerebral infarction.

Conclusion: Loneliness was correlated with cognitive decline and the development of dementia that was similar to Alzheimer's disease. This was true even when controlling for social isolation and other study variables. Loneliness, however, was not associated with the brain neuropathology that occurs with Alzheimer's disease or cerebral infarction, which suggests that there may be another neurobiologic mechanism involved.