Self-reported feelings of frequent loneliness or lack of close friends as a child or teenager were associated with greater likelihood of cognitive decline and incident dementia in middle-to-late adulthood, a retrospective study of almost 14,000 people revealed.

Whether or not people experienced loneliness as an adult did not significantly modify the strength of the associations, which suggests loneliness early in life could be an independent risk factor, investigators said.

“These findings highlight that childhood loneliness may have enduring implications for cognitive health and dementia risk across the lifespan,” lead author Jinqi Wang, PhD, of the Department of Epidemiology and Health Statistics, School of Public Health, Capital Medical University, Beijing, China, and co-authors wrote.

The study was published online on September 12 in JAMA Network Open. 

Understudied Problem

Studies examining the long-term effects of childhood loneliness are scarce, even though data suggest 13.2% of children worldwide experience loneliness. The new work is the first to find associations between loneliness before age 17 years and cognitive deficits and dementia at or after age 45 years, the researchers noted.

Data from the China Health and Retirement Longitudinal Study involved 17,707 participants enrolled in 2011. Assessment of childhood loneliness was done from face-to-face interviews during a 2014 Life History Survey. The current work included data from regular follow-ups until 2020 to avoid bias regarding loneliness during the COVID pandemic.

After exclusions, 13,592 participants (mean age, 58 years; 53% women) were studied for childhood loneliness and dementia risk, whereas 10,880 participants were included in the analyses of cognitive decline.

The researchers examined cognitive function using episodic memory and executive function measures. They identified dementia as coexistence of cognitive and functional impairments or on the basis of a reported physician diagnosis.

When asked about their childhood, 6.5% said they were often lonely because they had no friends, and 50% said they did not have a close friend as a child. 

The 565 participants (4.2%) who reported both feeling lonely often and not having a close friend were classified as having childhood loneliness. Both factors were independently and significantly associated with faster cognitive decline. 

Another 6526 participants (6.5%) who met only one criterion had “possible childhood loneliness.”

Important Implications

After adjusting for potential confounders, researchers linked childhood loneliness to lower baseline global cognitive Z scores (β, -0.14; 95% CI, -0.21 to -0.06 SD). 

Childhood loneliness was also associated with significantly faster cognitive decline in adulthood (β, -0.03; 95% CI, -0.05 to -0.02) than no childhood loneliness.

During a median follow-up of 7 years, 5.1% of participants developed incident dementia.

Adults who reported childhood loneliness were 41% more likely to develop dementia (adjusted hazard ratio, 1.41; 95% CI, 1.03-1.93) than those who did not. There was no association between possible childhood loneliness and dementia.

Self-reported loneliness was a potential limitation, as was classifying loneliness based on answers to two standard questions. Also, the observational study design means unmeasured confounders could exist.

The findings add to a growing body of evidence pointing to a link between loneliness and increased risk for dementia, cognitive decline, and brain atrophy. But prior studies focused primarily on loneliness in middle-to-late adulthood. 

“Our study broadened the perspective to the entire life course and found that individuals who experienced childhood loneliness, even in the absence of adult loneliness, still exhibited accelerated cognitive decline and elevated dementia risk,” investigators noted.

“Our findings have important implications for promoting later-life cognitive health and underscore the urgent need to identify, prevent, and address childhood loneliness through concerted efforts by families, schools, healthcare practitioners, and policymakers,” they added.

The study was independently supported. The authors reported having no relevant financial relationships.