New York:Lonely people may face the risk of developing Alzheimer's disease, aprogressive brain disorder that gradually destroys a person's memory andability to reason or make judgments, according to a study.

Professor Robert Wilson and colleagues at Rush UniversityMedical Centre studied more then 800 elderly patients who were followed over afour-year period, reported the online edition of BBC News.

The researchers assessed the loneliness of participants byasking people to rate from one to five whether they agreed with certainstatements related to loneliness on an annual basis.

"The researchers said in the "Archives of GeneralPsychiatry" journal that apart from an emotional impact, loneliness has aphysical impact, too. People who are lonely are twice as likely to developAlzheimer's disease," they added.

"It may be that loneliness affects brain systems dealing withcognition and memory, making lonely people more vulnerable to effects ofage-related decline in neural pathways, "Wilsonsaid. 

"This is an impressive study. It follows a large groupof people for a significant period of time and comes up with startling findingsthat back up earlier studies examining social interaction and Alzheimer'srisk," said Rebecca Wood, the chief executive of the Alzheimer's ResearchTrust.

"What I find particularly interesting about this studyis the fact that it is an individual's perception of being lonely rather thantheir actual degree of social isolation that seems to correlate most closelywith their Alzheimer's risk," she added.

Social isolation has already been shown to be linked todementia, but this is the first time researchers have looked at how alonepeople actually felt.