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An invited review co-authored by The Hormel Institute, University of Minnesota’s Leena Hilakivi-Clarke, PhD, Professor of Food Science and Nutrition, and Fabia De Oliveira Andrade, MSc, PhD, was recently published in Endocrinology. 

The paper examines the connections among social isolation, stress, microbiota composition in the body, and breast cancer risk and mortality. Better understanding of how these factors are related could lead to the development of new strategies to reduce breast cancer risk and mortality.

Loneliness isn’t simply an unpleasant feeling. As social animals, loneliness also has detrimental — and potentially deadly — consequences for humans’ mental and physical health. 

The Centers for Disease Control and Prevention (CDC) acknowledges that social isolation is a widespread public health concern in the United States. Studies have shown that social isolation — defined here as a lack of perceived social connections—can increase a person’s risk of premature death across all causes, just as smoking, obesity, physical inactivity, or high blood pressure do — and there are still health risks even if a person doesn’t necessarily feel lonely.

Factors that can lead to social isolation include aging, discrimination, poverty, violence, disability, epidemics, and more. Social isolation can increase a person’s risk for stroke, ischemic heart disease, type 2 diabetes, dementia, hospitalization, depression, anxiety, and suicide—the list goes on.

And there may be yet another factor to add to the long list of social isolation’s potential health impacts: the risks for developing breast cancer and breast cancer mortality. The invited review analyzes existing scientific literature to shed insight on how they may be linked. 

“It is still not clear how social isolation promotes diseases such as breast cancer, but it is known that social isolation can affect many signals in the body, such as the release of stress hormones which then cause inflammation and impair cellular metabolism,” Andrade said. “The most interesting and recent evidence is that stress also affects the gut microbiota and the resulting gut dysbiosis can be the main mediator of social isolation in impairing human health.”

While life stressors examined more broadly show inconclusive results related to breast cancer risk, stress related to social isolation shows a stronger link to breast cancer risk and mortality. Social isolation can set off a chain reaction of adverse responses in the body that may lead to increased breast cancer risk and mortality. When a person experiences social isolation, the body releases the neurotransmitter catecholamines as a stress response. 

Catecholamines from the sympathetic nervous system are bodily messengers that can then induce gut dysbiosis, a state of imbalance between helpful and harmful bacteria in the gut. Gut dysbiosis, in turn, leads to reduced production of short chain fatty acids (SCFAs), which play an important role in immune responses. Low levels of SCFAs may explain impaired cellular metabolism and immunosuppressive responses — changes that would thus lead to increased breast cancer risk and mortality.

“Since social isolation can have deadly consequences and the causes of social isolation are multifactorial, it is urgent to define strategies to block the effects of social isolation to prevent breast cancer and decrease mortality,” Hilakivi-Clarke said. “Because social isolation may affect breast cancer mainly by altering gut microbiota, attempting to restore the balance of the gut microbiota might be a potential strategy to prevent breast cancer and reduce mortality.”

This paper was written with support from The Hormel Institute’s Internal Grants Program. These grants are made possible thanks to community fundraisers including Paint the Town Pink, Eagles Cancer Telethon, Karl’s Tourney/Karl Potach Foundation, Bowling for the Battle, and Blooming Prairie Cancer Group.

You can access the article online via the Oxford Academic platform.