Loneliness can be a sign for development of the type of dementia linked to Alzheimer's disease in late life, according to a new study published in the February issue of Archives of General Psychiatry, one of the JAMA/Archives journals.

The study by researchers at Rush University Medical Center, Chicago found those lonely elderly people may be twice as likely to develop Alzheimer’s type of dementia as those who are not lonely, according to the study.

Earlier studies have associated social isolation with an increased risk for dementia, according to background information in the article.   Social isolation is often found in unmarried people who have a small social network and are not active in socializing with others.

The researchers said little research has been done to establish an association between dementia and emotional isolation, or loneliness, which the authors of the study said refers to perceived social isolation and feeling disconnected from others.   Feeling lonely does not mean physically keeping away from others, rather dissatisfied with social interactions, according to the researchers.

To inquire about the association between loneliness and Alzheimer's disease, Robert S. Wilson, Ph.D., and colleagues studied 823 people with an average age of 80.7 between November 2000 and May 2006.

They evaluated the participants at the beginning of the study and then every year for four years to assess loneliness, classifications of dementia and Alzheimer’s disease, and testing of their thinking, learning and memory abilities.

They measured loneliness on a scale of one to five, with higher scores indicating more loneliness.   At the beginning of the study, the average score of loneliness for all participants was 2.3.    During the study, 76 individuals were diagnosed with dementia that met criteria for Alzheimer’s disease.

Increase by one point on the loneliness scale indicated that the subjects' risk for developing Alzheimer's disease increased 51 percent, the researchers found. Those with their loneliness score at 3.2 were 2.1 times more likely to develop Alzheimer's compared to those with their score at 1.4   The link was still significant even after markers of social isolation such as a small social network and infrequent social activities were considered.

The association does not mean a causal relation between loneliness and Alzheimer's disease.   It could be that loneliness affects Alzheimer's or vice versa.   Or both are a result of a third factor.

However, the researchers said that loneliness may be a risk factor for Alzheimer's because autopsies on 90 individuals who died during the study showed that loneliness during life was not related to any brain changes associated with Alzheimer’s disease, including nerve plaques and tangles, or tissue damaged by lack of blood flow.

The autopsy results seemed to be contradictory to the statistical correlation between Alzheimer’s disease and loneliness.   A scientist affiliated with foodconsumer.org who is not a social scientist suggested that there might be a common factor connecting Alzheimer’s and loneliness.

But the authors write “The results suggest that loneliness may contribute to risk of an Alzheimer’s disease–like dementia in late life and does so through some mechanism other than Alzheimer’s disease pathology and cerebral infarction,” or the cutoff of blood supply to the brain.

An early study demonstrated that dementia or not was not associated with feeling lonely.  In a study of 589 persons in Sweden, Holmen K and colleagues from H.M. Queen Sophia University College of Nursing in Stockholm found that "non-demented elderly subjects reported themselves to be lonely significantly less often compared to demented subjects but there were no difference in the emotional experience of loneliness," which seems contradictory to the finding of the current study.

The study, published in the December 2000 issue of Archives of gerontology and geriatrics, also showed that social loneliness was more common in people with different levels of dementia and increased with reduced cognitive function while emotional loneliness decreased.

Still, it remains unclear which causes which.   Further studies are needed to help explain the association between loneliness and Alzheimer’s disease.