​New York, Nov 3 (IANS) The constant feeling of being lonely and isolated may be due to the increased amyloid levels in the brain and can be indicative of preclinical Alzheimer's disease, researchers have found.

Loneliness -- characterised by subtle feelings of social detachment -- may be associated with early brain changes in preclinical Alzheimer's disease, prior to mild cognitive impairment.

The findings showed that higher brain amyloid burden was associated with more frequent feelings of isolation, being left out, and lacking companionship, independent of sociodemographic factors, objective measures of social network, depressive and anxiety symptoms.

"The study reports a novel association of loneliness and cortical amyloid burden in cognitively normal adults and present evidence for loneliness as a neuropsychiatric symptom relevant to preclinical Alzheimer's disease," said Nancy J. Donovan, M.D., of Brigham and Women's Hospital and Harvard in Boston.

Emotional and behavioural symptoms in cognitively normal older people may be direct manifestations of Alzheimer's disease (AD) pathophysiology at the preclinical stage, prior to the onset of mild cognitive impairment, the study stated. 

For the study, the team included 43 women and 36 men with an average age of about 76 years. Out of these, 22 (28 per cent) were carriers of the genetic risk factor apolipoprotein, and 25 (32 per cent) were in the amyloid-positive group based on volume in imaging. 

The participants' average loneliness score was 5.3 on a scale of 3 to 12.

Higher cortical amyloid levels were associated with greater loneliness after controlling for age, sex, genetic risk, socioeconomic status, depression, anxiety and social network. 

The participants in the amyloid-positive group were 7.5 times more likely to be classified as lonely than non-lonely compared with individuals in the amyloid-negative group. 

The association between high amyloid levels and loneliness was also stronger in APOE 4 carriers than in non-carriers.

"The study will inform new research into the neurobiology of loneliness and other socioemotional changes in late life and may enhance early detection and intervention research in Alzheimer's disease," Donovan said in the study appearing online in the journal JAMA Psychiatry.