Recently I saw a very lonely freshman college student who had come to the Bay Area from another state leaving family and high school friends behind to make her way in a new social ecosystem. That experience got me thinking about a number of papers I had read about loneliness over especially the last ten years. The first paper I read about social isolation and its effects on mortality was in the Science in the late 1980s. Following that were a steady stream of papers documenting the unhealthy changes in cardiovascular, immune, and nervous system which is undoubtedly related to the reduction in life expectancy of lonely people. I should add that it is not the number of social contacts that is important but the subjective experience of loneliness. Feeling alone and being alone are not identical concepts. Some people are socially isolated but don't feel lonely.
Lonely people tend to show changes in physiology, e.g., higher vascular tone leading to increased resistance to blood flow and thus imposing an added burden to cardiac function. They also tend to have higher cortisol and epinephrine levels in urine and saliva. These are signs of an overly active sympathetic nervous system. From an evolutionary standpoint this makes good sense because it signals that the social ties to the tribe are too weak and thus one's genetic contribution is in danger (decreased fitness) because the individual has abandoned the protection of the group. So it's an aversive signal that will increase the chances of passing on the individual's genes (increased fitness). So it's adaptive in the short term but unhealthy over the long term.
Several papers from geneticists at UCLA have demonstrated increased activity of a number of genes promoting inflammation and decreased activity of genes that retard inflammation and thus cardiovascular disease associated with inflammation. Genes affecting the immune system are also suppressed leading to increased susceptibility to viral infections.
Loneliness also has an effect on sleep. Lonely people sleep a normal number of hours but tend to awaken unrest-ed and fatigued. They also get less enjoyment from leisure activities. Social psychologists have characterized lonely people's view of social interactions as negative and their view of others as negative. They pay more attention to negative social cues than others do. As with other mental states, certain researchers are using MRIs and other tools to tie a specific brain region to the feeling. In this case the ventral striatum was found to be less active.
In the 2008 book, Loneliness: Human Nature and the Need for Social Connection, John Cacioppo, the author and a social psychologist at the University of Chicago, postulated that there is a "genetic thermostat" for loneliness that has different set points in different people. He further states, "You're not inheriting loneliness; you're inheriting how painful it feels to be alone."
How does this inform me about treating patients such as the abovementioned college freshman? It leads to specific advice about lifestyle choices and further to challenge the negative view of social situations with alternative explanations which over time should result in a more positive experience.