# Association of loneliness and social isolation with excess risk of mental disorders in people with obesity: a prospective cohort study

## TL;DR

This study shows that loneliness and social isolation increase the risk of mental disorders in obese individuals more than in non-obese individuals.

## Contribution

The study identifies loneliness and social isolation as significant predictors of mental disorders in obese populations.

## Key findings

- Obese individuals with higher loneliness had a 1.73 times higher risk of mental disorders compared to the least lonely group.
- Alleviating loneliness and social isolation can reduce the mental health risks associated with obesity.
- Loneliness and social isolation ranked among the top risk factors for mental disorders in obese individuals.

## Abstract

Loneliness and social isolation are more prevalent among obese individuals. This study aims to explore the association of the level of loneliness and social isolation with the excess risk of mental disorders among obese people compared with non-obese people.

A total of 219,086 participants (109,543 obese participants and 109,543 matched non-obese participants) from the UK Biobank were included at baseline. Loneliness and social isolation were assessed using a two-item scale and a three-item scale, respectively. Incident mental disorders, including substance use, psychotic disorders, mood disorders, depression, anxiety disorders, post-traumatic stress disorder, and behavioral syndromes, were ascertained through linkage to primary and secondary care records.

During a median (IQR) follow-up of 12.40 (11.50–13.20) years, a total of 18,280 obese participants developed mental disorders. Compared to the least lonely group, obese people in the moderate and most lonely groups had a significantly and progressively higher risk of mental disorders (moderately lonely: HR 1.37, 95% CI 1.33–1.42; most lonely: HR 1.73, 95% CI 1.65–1.81; P-trend < 0.001). We observed a similar pattern in terms of social isolation. The relative importance of loneliness and social isolation in predicting mental disorders ranked third and eighth among traditional risk factors. Compared to non-obese individuals, the excess risk of mental disorders for obese individuals varied considerably by levels of loneliness and social isolation, with HRs ranging from 1.05 in the least lonely to 1.79 in the most lonely, and from 1.14 in the least isolated to 1.36 in the most isolated.

Alleviating loneliness and social isolation was associated with lower obesity-related excess risk of mental disorders. Our finding suggests the incorporation of social networking platforms and support systems into intervention strategies to effectively mitigate the mental health issues in obese population.

Clinical trial registration number: Not applicable. (This study is an observational analysis based on UK Biobank data and does not involve a clinical trial. This research was conducted under UK Biobank application no. 88159. The UK Biobank study was approved by the North West Multi-Centre Research Ethics Committee (11/NW/0382). All participants provided informed consent through electronic signature at baseline assessment.)

The online version contains supplementary material available at 10.1186/s12963-025-00451-4.