New York, Nov 24 (IANS): For older adults, perceived social isolation is a major health risk that can increase the chances of premature death by 14 percent.

The researchers found that loneliness leads to fight-or-flight stress signalling, which can ultimately affect the production of white blood cells.

Essentially, lonely people had a less effective immune response and more inflammation than non-lonely people, researchers from the University of Chicago and the University of California-Los Angeles found.

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

As expected, the leukocytes of lonely humans and macaques showed an increased expression of genes involved in inflammation and a decreased expression of genes involved in antiviral responses.

"Leukocyte gene expression and loneliness appear to have a reciprocal relationship, suggesting that each can help propagate the other over time," the researchers noted.

These results were specific to loneliness and could not be explained by depression, stress or social support.

"The 'danger signals' activated in the brain by loneliness ultimately affect the production of white blood cells. The resulting shift in monocyte output may both propagate loneliness and contribute to its associated health risks," the researchers said.

The study was published in the Proceedings of the National Academy of Sciences.