How loneliness leads to poor health

By Priyanjana Pramanik, MSc.Reviewed by Lily Ramsey, LLMFeb 3 2025

A large cross-sectional study finds that loneliness is associated with higher risks of smoking, physical inactivity, poor diet, and obesity, highlighting its impact on public health and the need for targeted interventions.

Study: Loneliness is associated with adverse health behaviour and obesity: a Danish population-based study of 122,258 individuals. Image Credit: New Africa/Shutterstock.com

In a recent study published in BMC Public Health, researchers explored how loneliness might lead to unhealthy habits and obesity, explaining why lonely people are more likely to experience adverse health outcomes.

Their findings indicate that lonely people are more likely to smoke, follow unhealthy diets, and suffer from obesity; they are also less likely to be physically active. Notably, lonely men are less likely to consume large amounts of alcohol.

Background

Loneliness, which researchers define as a negative emotional condition caused by the gap between how much social interaction a person wants to have and how much they have, can be deadly. Lonely people have higher mortality rates and are more likely to suffer from heart disease, type 2 diabetes, and depression.

What drives these relationships? Researchers hypothesize that diet, physical inactivity, and smoking could be the cause. In the absence of social support and cues, lonely people could adopt unhealthier habits. They could also face challenges regulating their impulses or dealing with adversity.

Despite these theories, literature reviews suggest that the statistical evidence of these relationships is mixed.

The links may also be bidirectional; while lonely people show higher rates of obesity, individuals with a higher body mass index (BMI) are more likely to be lonely. Existing studies face challenges, including small effect sizes, lack of generalizability, and unreliable measures of loneliness.

About the study

Researchers investigated how loneliness is associated with obesity and health-related habits such as drinking, smoking, exercise, and diet. They applied a cross-sectional design that used a study from a national survey conducted in Denmark in 2017.

The survey collected information on people over 16 at the national and regional level, including information on weight, height, health habits, and sociodemographic characteristics (partnership status, country of origin, educational level, age, and sex). It achieved a final sample size of 122,258 individuals.

Loneliness was measured using a three-item scale that assessed feelings of being left out, absence of companionship, and isolation. On a scale of three to nine, a score of seven or more indicated that a person was lonely.

People were considered to have unhealthy habits if they followed an unhealthy diet (measured by lower-than-recommended consumption of fish, vegetables, and fruits and high consumption of saturated fats), consumed more than 10 units of alcohol in a week, smoked daily, and did not meet guidelines for physical activity.

Researchers used statistical models to estimate the odds ratios for the relationships between loneliness, health-related habits, and obesity after adjusting for sociodemographic characteristics.

Findings

On analyzing the data, researchers discovered that 8.2% of the population could be classified as lonely. Lonely people were less likely to live with a partner and be Danish. Younger people, women, and those enrolled in educational programs were all more likely to be lonely.

Examining obesity levels among lonely people, researchers found that 21.4% of lonely people were obese compared to 15.4% of non-lonely people. They were more likely to unhealthy diets (22.6% compared to 14.7%), be physically inactive (41.8% compared to 28.6%), and smoke daily (22.7% compared to 15.8%).

Notably, they were slightly less likely to exhibit high levels of alcohol consumption. These relationships remained after adjusting for sociodemographic characteristics.

Researchers also found that while loneliness was linked to obesity and poor health outcomes for men and women, the relationship was stronger for women. However, while lonely men showed a lower likelihood of consuming high levels of alcohol, women did not.

The influence of loneliness on obesity and health-related habits showed some variation across life stages. For example, obesity and loneliness showed the strongest association among adolescents and young adults and no association during old age.

Conclusions

Findings from this study support previous work that shows positive relationships between loneliness and smoking, except during early and middle adulthood.

Since the majority of smokers adopt the habit before their 18^th birthday, addressing loneliness among adolescents could lead to significant public health benefits.

Regarding alcohol consumption, researchers found that lonely men (but not women) are less likely to drink more than 10 units of alcohol a week.

This can be explained by the importance of social drinking in Danish culture, and this relationship may not be generalizable to other contexts where the prevalence of solitary drinking could lead to a positive association.

Loneliness was associated with obesity, poorer diet, and low levels of physical exercise. These relationships may have behavioral and psychological mechanisms, where weight stigmatization and lack of support could lead to unhealthy coping strategies and further social isolation.

These findings provide important insights into why loneliness is a silent killer. Social isolation has become a widespread global problem, and interventions to promote healthy behaviors would benefit from also targeting social connectedness to improve health and well-being.