science newsletter New study links loneliness to cardiovascular diseases, stroke and mortality 

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A new study published January 3, 2025, in Nature Human Behaviour journal, has found that loneliness and social isolation in humans can be linked to cardiovascular diseases, stroke and mortality.

The study was conducted by researchers at Fudan University in Shanghai, China, and the University of Warwick in the United Kingdom. They studied data from 42,062 people with an average age of around 56 years, and analysed 2,920 proteins in their blood samples. Researchers also followed up on health data from the subjects for 14 years.

The researchers analysed protein levels in subjects and how they express themselves to correlate them with social isolation and loneliness. With the study, the researchers wanted to answer two questions:

1. Which proteins are associated with social isolation and loneliness?
2. How do they contribute to the relationship of social isolation, loneliness and health? 

Here is what they found. 

The researchers noted a protein that is an inflammatory marker, and doesn’t normally express in tissues, showed the strongest association with social isolation, while another protein that regulates cholesterol level in blood was strongly associated with loneliness.  

The study used Mendelian Randomisation (MR), which is a scientific method that uses genetic variants (and hence, protein structures) to establish causal relationships between variables. Overall, it found that loneliness contributed to an increase in five specific proteins. These proteins showed associations with metabolic processes and blood components like cholesterol levels and lipid profiles, as well as brain region volumes that are linked to the ability to sense physiological conditions within the body, and emotional and social processes.  

Through these MR-identified proteins, the researchers established a mediating effect between loneliness and cardiovascular diseases, stroke, and mortality. For example, a one-unit increase in one of these proteins was linked to a 58% increase in mortality risk. Overall findings of the study support the hypothesis that social relationships indirectly influence morbidity and mortality. 

The researchers, however, also noted that although causal effects of loneliness on five specific proteins were observed across multiple analytical methods, it is possible that one genetic variant can influence multiple traits through related pathways, potentially confusing the results. This is a common problem with MR studies, and more investigations in larger datasets are needed to know if the associations observed in this study are due to direct cause-and-effect relationships. 

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