It’s well established that loneliness can affect a person’s health. For example, Julianne Holt-Lunstad, a professor of psychology and neuroscience at Brigham Young University, has published several major studies offering a statistical view:

Holt-Lunstad’s first study examined the extent to which social relationships and other social indicators, such as size of social network and perceived social support, influence one’s risk for mortality. The analysis — which involved over 300,000 participants — found that scoring low on those indicators of social connection carried a similar risk to smoking up to 15 cigarettes per day, Holt-Lunstad told INSIDER. Participants with stronger relationships were found to have a 50% increased likelihood of survival. The second study involved 3.4 million participants and focused on subjective loneliness and actual, physical social isolation, and found that both can lead to a 30% increased risk of premature death. Holt-Lunstad said this risk exceeds that of obesity, physical inactivity, and air pollution. Sarah Schmalbruch, “10 ways loneliness can affect your health — physically and mentally” at Insider (Papers.)

Loneliness is understood in this type of research as an emotional state rather than a physical one. We can be lonely in a crowd or delighted with an entire week of solitude to finally finish a project. It’s the emotional state that is bad for human health.

What’s less often recognized is that loneliness could cause be a cause of brain damage as well, at least if we go by rodent studies. Obviously, we can’t do this study on humans:

Mice yanked out of their community and held in solitary isolation show signs of brain damage. After a month of being alone, the mice had smaller nerve cells in certain parts of the brain. Other brain changes followed, scientists reported at a news briefing November 4 at the annual meeting of the Society for Neuroscience… Neurobiologist Richard Smeyne of Thomas Jefferson University in Philadelphia and his colleagues raised communities of multiple generations of mice in large enclosures packed with toys, mazes and things to climb. When some of the animals reached adulthood, they were taken out and put individually into “a typical shoebox cage,” Smeyne said.

This abrupt switch from a complex society to isolation induced changes in the brain, Smeyne and his colleagues later found. The overall size of nerve cells, or neurons, shrunk by about 20 percent after a month of isolation. That shrinkage held roughly steady over three months as mice remained in isolation… The researchers uncovered other worrisome signals, too, including reductions in a protein called BDNF, which spurs neural growth. Levels of the stress hormone cortisol changed, too. Compared with mice housed in groups, isolated mice also had more broken DNA in their neurons.

Laura Sanders, “Loneliness is bad for brains” at Science News Paper.

We don’t know for sure whether loneliness leads to brain damage in humans but recent rodent studies are sobering reminders, especially where elderly people or those living in institutions are concerned: What we think about our lives really does affect our health.

See also: Yes, your brain is a machine – if you choose to see it that way (Michael Egnor)

and

The brain is not a meat computer. Dramatic recoveries from brain injury highlight the difference (Michael Egnor)