Researchers have long known the dangers of loneliness, especially among the elderly, but the cellular mechanisms by which loneliness causes adverse health outcomes have not been well understood. Now a team of researchers, including Chicago psychologist and leading expert John Cacioppo, has released a study shedding new light on how loneliness triggers physiological responses that can ultimately make us sick.

The paper, which appears Nov. 23 in the Proceedings of the National Academy of Sciences, shows that loneliness leads to fight-or-flight stress signaling, which can ultimately affect the production of white blood cells.

Previous research from this group had identified a link between loneliness and a phenomenon they called “conserved transcriptional response to adversity” or CTRA. This response is characterized by an increased expression of genes involved in inflammation and a decreased expression of genes involved in antiviral responses. Essentially, lonely people had a less effective immune response and more inflammation than non-lonely people.

For the current study, the team examined gene expression in leukocytes, cells of the immune system that are involved in protecting the body against bacteria and viruses.