# Adolescent loneliness as a predictor of adult obesity: a longitudinal analysis from the HUNT study, Norway

## TL;DR

This study finds that feeling lonely as a teenager is linked to a higher risk of obesity in adulthood, especially for males.

## Contribution

The study provides new evidence that adolescent loneliness predicts adult obesity, with sex-specific differences in risk.

## Key findings

- Adolescent loneliness is associated with increased adult obesity risk, particularly for males.
- The prevalence of obesity nearly quadrupled from adolescence to adulthood in both sexes.
- Lonely males had higher odds of obesity and greater BMI increases compared to females.

## Abstract

Obesity and loneliness are growing public health concerns with potential long-term health implications. Although both issues have been extensively studied separately, the relationship between adolescent loneliness and adult obesity remains underexplored. This study aimed to investigate the associations between self-reported loneliness during adolescence and obesity in adulthood, analyze trends in loneliness and obesity among adolescents and young adults, and examine potential sex differences in these associations.

This prospective study used data from The Trøndelag Health Study (HUNT) in Norway. The initial data collection focused on adolescents aged 13–19 years in 2006–2008 (Young-HUNT3), with a follow-up conducted in 2017–2019 (HUNT4) when participants were 23–31 years old; in total, 2,293 respondents (1,320 females and 973 males) were included. Loneliness was assessed using a single-item questionnaire, whereas obesity was assessed via body mass index (BMI) and waist circumference (WC). Multinomial logistic and linear regression models adjusted for covariates were used to analyze the associations between adolescent loneliness and adult obesity.

The prevalence of obesity increased significantly from adolescence to adulthood in both sexes, and the proportion of obese individuals increased from 4.0 to 16.6% in females and from 6.4 to 18.3% in males. Loneliness rates decreased in females but remained stable in males. Adolescents experiencing frequent loneliness showed a higher obesity risk in young adulthood than their less lonely peers. This relationship persisted after adjusting for confounding factors. Lonely adolescent males presented greater odds of BMI-defined obesity (OR 2.60, 95% CI: 1.12– 6.06) and greater BMI increases (1.97 kg/m², 95% CI: 0.38– 3.55) than females did (OR 1.82, 95% CI: 1.03– 3.22; BMI increase 1.16 kg/m², 95% CI: 0.01–2.31) later as adults.

This study suggests that loneliness in adolescence may be a risk factor for BMI-defined obesity and increased WC in adulthood, with some variations in the strength of associations observed across sexes. The findings highlight the critical need to address loneliness as a public health concern and underscore the importance of a comprehensive approach to adolescent health, considering the long-term associations between social and emotional well-being on physical health outcomes.

The online version contains supplementary material available at 10.1186/s12889-025-23872-0.