Is it really true that loneliness causes illness?



There are countless studies showing the relationship between loneliness and health risks, such as

one that shows that loneliness doubles the risk of diabetes and another that shows that loneliness ages people faster than smoking. For this reason, loneliness itself is often considered a health risk, but a new analysis using genetic data has produced results that cast doubt on the conventional wisdom that loneliness causes disease.

Observational and genetic evidence disagree on the association between loneliness and risk of multiple diseases | Nature Human Behavior
https://www.nature.com/articles/s41562-024-01970-0

Loneliness may not be a direct cause of disease
https://www.news-medical.net/news/20240917/Loneliness-may-not-be-a-direct-cause-of-disease.aspx

Genetic analysis challenges the idea that loneliness directly causes diseases
https://www.news-medical.net/news/20240918/Genetic-analysis-challenges-the-idea-that-loneliness-directly-causes-diseases.aspx

Loneliness/Disease Link Debatable?
https://www.medscape.com/viewarticle/loneliness-disease-link-debatable-2024a1000ha5

According to a research team led by Jihui Zhang of Guangzhou Medical University, although there are many studies showing the relationship between loneliness and disease, the mechanism behind why loneliness worsens health remains largely unknown.

This is because observational studies that collect and analyze data can find some connection between loneliness and health problems, but often do not determine whether there is a causal relationship that 'loneliness causes the illness.'

Therefore, we cannot rule out the possibility of a 'reversal of causality' - for example, when illness reduces social participation and ultimately leads to loneliness - or that a 'confounding factor' other than loneliness is associated with both loneliness and illness.



To better understand the link between loneliness and disease, the research team analysed a combination of behavioural, genetic and hospital admission data collected from the UK Biobank, a large-scale longitudinal study conducted in the UK.

The data covered 56 major diseases, the median follow-up period was 12 years, and the average age of the 476,100 participants was 56.5 years old. 23,136 people, or about 5% of the total, were judged to be lonely using the UCLA Loneliness Scale developed by researchers at the University of California, Los Angeles.

The team first conducted a standard analysis of hospital admission data and death records and found that loneliness was associated with a higher risk of 30 of 56 diseases, including post-traumatic stress disorder (PTSD), depression, anxiety, schizophrenia, and chronic obstructive pulmonary disease (COPD).

In addition, the research team also conducted an analysis using

Mendelian randomization (MR) analysis of genetic data. MR analysis is a method to reduce bias in the analysis results by utilizing Mendel's law, which states that genetic mutations are randomly inherited from parents to children. By focusing on genetic mutations that are known to be associated with a specific disease and are not influenced by the environment or lifestyle, it is possible to reduce causal reversal and the influence of confounding factors.



The research team performed MR analysis on 26 of the 30 diseases that were significantly associated with loneliness and for which genetic data was available, and found that most diseases had no causal relationship with loneliness.

Of the 26 diseases, a potential causal relationship was only found for six: hypothyroidism, asthma, depression, psychotropic drug abuse, sleep apnea, and hearing loss.

These findings suggest that loneliness is not a direct cause of disease but rather a 'sign of disease,' and therefore addressing loneliness alone may not reduce the risk of disease.

'Loneliness is not a causal risk factor for most diseases but may serve as a potential surrogate marker,' the team wrote in their paper.

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