Social isolation poses greater mortality risk than loneliness in obese individuals, study finds

By Neha MathurReviewed by Benedette Cuffari, M.Sc.Jan 24 2024

In a recent study published in JAMA Network Open, researchers examine the associations of social isolation and loneliness with the risk of mortality in individuals with obesity versus normal-weight individuals.

Study: Improvement of Social Isolation and Loneliness and Excess Mortality Risk in People With Obesity. Image Credit: KieferPix / Shutterstock.com

The relationship between obesity, social isolation, and loneliness

Obesity leads to various metabolic disorders ranging from type 2 diabetes (T2D) and chronic inflammation to cardiovascular disease (CVD) and cancer. The prevalence of obesity is rising, with about 30% of people in high-income countries (HICs) considered obese.

Likewise, loneliness is becoming a global public health crisis. Alongside social isolation, loneliness is a crucial social determinant of health; however, these two factors correlate differently with mortality.

Social isolation reflects the scarcity of contact with others in general, while loneliness represents a sense of detachment potentially linked to emotional states like depression. Thus, one can experience loneliness even when living with others.

In the absence of support, these two factors may exacerbate the health behaviors of people with obesity. For example, obese people often experience greater levels of social isolation and loneliness than non-obese individuals.

About the study

In the present study, researchers screened the United Kingdom Biobank to identify obese and non-obese individuals based on body mass index (BMI). BMI values over and under 30 reflected obese and non-obese individuals, respectively. The study cohort comprised obese individuals and an equal number of non-obese individuals randomly matched based on age, gender, and assessment center.

The primary outcomes were all-cause mortality and mortality from cancer and CVD based on International Statistical Classification of Diseases and Related Health Problems (ICD) codes C00-C97 and I00-I99. The study end date was the date of death or November 27, 2021, whichever came first. 

Social isolation and loneliness were defined based on self-reported questionnaires in the U.K. Biobank. The researchers also investigated whether the obesity-related excess mortality risk could be removed or weakened by improving social isolation and loneliness indices. 

Data on several variables were collected from the U.K. Biobank including age, gender, race/ethnicity, educational status, smoking status, alcohol consumption, and glycated hemoglobin (HbA1c) levels. After that, study participants were classified based on their weekly physical activity levels of less than or greater than 150 minutes.

Each participant's metformin and glucocorticoid use, as well as their self-reported history of depression, anxiety, eating disorders, hypertension, high cholesterol, and diabetes, were also recorded.

Fisher exact or Wilcoxon rank-sum tests were used to examine participant characteristics based on obesity status. Additionally, Cox regression models determined the association of social isolation and loneliness with all-cause, cancer- and CVD-related mortality in obese people. 

Another statistical model helped the researchers determine the contribution of social isolation and loneliness to the relative risk in people with obesity against lifestyle-related risk factors for mortality, including depression, anxiety, and the Townsend Deprivation Index among people with obesity. Two sensitivity analyses were also performed to ensure the stability of the results.

Study findings

The study included 398,972 participants, 55.3% of whom were women, with an average age of 55.9 years. Of the study cohort, 93,357, or 23.4%, were obese, whereas 305,615, or 76.6%, were non-obese.

Among the obese participants, 48.9%, 40.6%, and 10.5% had a social isolation index of zero, one, and over two, which reflected no, mild, and moderate-to-severe social isolation, respectively. Loneliness indices of zero, one, and two also applied to 63.6%, 28.5%, and 7.9% of obese participants, respectively. 

As compared to controls, people with obesity had a markedly higher prevalence of social isolation and loneliness. Additionally, over a median follow-up of 12.7 years, 22,872 incident deaths, including 11,442, 4,372, and 7,058 cancer-, CVD-related and other deaths, respectively.

Of all mortality risk factors, social isolation ranked fourth in terms of strength, whereas loneliness was ranked fourteenth.

Conclusions

The current U.K. Biobank cohort study found that social isolation was more strongly associated with mortality than loneliness. Thus, preventing social isolation and mitigating its effects may be more beneficial for reducing the risk of all-cause and CVD-related mortalities than loneliness, lifestyle factors, depression, and anxiety in people with obesity.

Importantly, more intensive interventions are needed to improve social isolation in people with obesity than in people without obesity to lower the risk of mortality.