Loneliness expresses itself in our genes, according to new research.
US researchers have discovered that social isolation is linked to alterations in the activity of genes involved in the immune system.
Previous studies had shown that loneliness is linked to an increased risk of heart disease, viral infections and cancer, but now scientists are beginning to unpick the phenomenon at the molecular level.
The latest research shows that isolation impacts on inflammation, the first response of the immune system and, to a lesser extent, it also influences antiviral responses and antibody production.
Study author Steve Cole said: "What this study shows is that the biological impact of social isolation reaches down into some of our most basic internal processes the activity of our genes.
"These findings provide molecular targets for our efforts to block the adverse health effects of social isolation.
"We found that what counts at the level of gene expression is not how many people you know, it's how many you feel really close to over time."