Loneliness is associated with a 31% higher risk of developing dementia, finds largest study to date

New research published in Nature Mental Health confirms that loneliness is not just an emotional burden—it may also have serious consequences for brain health. In the largest study of its kind, researchers found that individuals who feel lonely are at a significantly increased risk of developing dementia, with a 31% higher likelihood than those who do not report feeling lonely. This discovery sheds light on the critical role of social connection in maintaining cognitive health and preventing dementia.

Loneliness is a deeply personal experience, defined not by the absence of people but by the absence of meaningful connections. It occurs when there is a mismatch between the social relationships an individual has and those they desire. Unlike social isolation, which refers to a lack of physical interaction or contact with others, loneliness is a subjective feeling. For example, a person surrounded by family or friends can still feel lonely if their emotional needs are unmet.

The motivation for the study stemmed from a growing body of evidence suggesting that loneliness has far-reaching health consequences, including links to cardiovascular disease, depression, and premature mortality. Recent research has also hinted at a connection between loneliness and dementia, but findings have been inconsistent. Some studies found a strong link, while others reported no association or effects limited to specific groups, such as men. Researchers recognized the need for a comprehensive analysis to clarify this relationship.

“I have always been interested in psychosocial factors that affect memory and cognitive functioning across the lifespan, from middle age to later adulthood,” said study author Martina Luchetti, an assistant professor at Florida State University College of Medicine.

“In recent years, I focused my research on loneliness and social relational aspects that affect the risk of cognitive impairment and dementia because our relationships—and how we are satisfied with them—impact how we function daily. Importantly, organizations such as the World Health Organization and the U.S. Surgeon General have recognized the public crisis of loneliness and are taking action to raise awareness and understand its consequences for our society,” she explained.

Luchetti and her research team conducted the largest meta-analysis to date exploring the connection between loneliness and dementia, analyzing data from 608,561 individuals worldwide. By pooling information from 21 longitudinal studies, they aimed to clarify whether loneliness increases the risk of dementia and uncover patterns across different populations and study designs.

The team included data from prominent aging cohort studies, such as the Health and Retirement Study in the United States and similar studies across Europe, Asia, and Latin America. Participants, all cognitively healthy at the outset, were surveyed about their feelings of loneliness using validated measures like the UCLA Loneliness Scale. These tools asked respondents how often they felt a lack of companionship, left out, or socially isolated. Over the years, participants underwent repeated assessments of cognitive health, which were evaluated using clinical diagnoses, neuropsychological tests, or self-reports of doctor-diagnosed conditions.

The findings showed a consistent link between loneliness and dementia. Individuals who reported feeling lonely were 31% more likely to develop dementia compared to those who did not feel lonely. The link between loneliness and dementia was comparable to other well-known behavioral risk factors, such as smoking or physical inactivity.

This association persisted even after accounting for factors such as social isolation, depressive symptoms, and physical health conditions like diabetes or hypertension, suggesting that loneliness independently contributes to cognitive decline.

“We found what we expected,” Luchetti told PsyPost. “There is mounting evidence of the association between loneliness and health outcomes, and evidence that connects loneliness to the risk of poor cognitive function even after decades.”

The researchers also found that loneliness was associated with specific types of dementia, including Alzheimer’s disease and vascular dementia. Interestingly, the relationship with vascular dementia appeared particularly strong, possibly due to the interplay between loneliness, stress, and cardiovascular health.

In addition to dementia, the researchers found that loneliness increased the likelihood of milder cognitive impairments, such as difficulties with memory or problem-solving, by 15%. These impairments often precede dementia, indicating that loneliness may affect cognition even in its earlier stages. The consistency of these results across different countries and populations underscores the universality of the relationship between loneliness and cognitive health, while highlighting potential avenues for intervention to mitigate these risks.

The researchers also explored possible mechanisms linking loneliness to dementia. One explanation is that loneliness may lead to reduced cognitive stimulation, as lonely individuals often withdraw from social and intellectual activities that support brain health. Chronic loneliness is also associated with stress and inflammation, which are known to damage brain cells over time. Additionally, lonely individuals may adopt unhealthy behaviors, such as physical inactivity or poor diet, which further increase the risk of dementia.

“The findings of this meta-analysis confirm that feeling lonely increases the risk of dementia—including cause-specific dementias, such as Alzheimer’s and vascular dementia—and extends the risk to cognitive impairment prior to dementia,” Luchetti explained. “There are different types and sources of loneliness that can affect cognitive symptoms across the dementia continuum. Addressing loneliness and promoting a feeling of connectedness could be protective for cognitive health in later life.”

Notably, when controlling for depression and social isolation, the association between loneliness and dementia was reduced in size but remained significant. The association was robust and independent of sample characteristics, such as age or sex. However, there was variability in the strength of the association across studies, which could be attributed to the use of different measures to assess both loneliness and cognitive status.

Despite its strengths, the study has limitations. First, most of the included studies measured loneliness at a single time point, which does not capture how loneliness changes over time. Future research should explore how persistent versus temporary loneliness impacts dementia risk. Additionally, while the analysis included diverse populations, more research is needed in underrepresented regions like Africa and South Asia to understand cultural variations in loneliness and its effects.

The researchers also noted that loneliness is a complex phenomenon, encompassing both emotional loneliness (the absence of close connections) and social loneliness (a lack of broader social networks). Understanding how these dimensions differ in their impact on cognitive health could inform targeted interventions.

“More work should be directed to identify the frequency, intensity, and types of loneliness over time and how transitions in and out of loneliness affect cognitive health,” Luchetti said.

The study, “A meta-analysis of loneliness and risk of dementia using longitudinal data from >600,000 individuals,” was authored by Martina Luchetti, Damaris Aschwanden, Amanda A. Sesker, Xianghe Zhu, Páraic S. O’Súilleabháin, Yannick Stephan, Antonio Terracciano, and Angelina R. Sutin.