Research has previously linked social isolation to poor health outcomes. Dr. John Cacioppo of the University of Chicago and colleagues reported in the Proceedings of the National Academy of Sciences USA that the experience of loneliness affects the body’s immune system and its ability to fight off infectious bacteria and viruses.

The scientists found that a weaker immune system predisposed subjects to lonely feelings a year or more later.

They found no link between the body’s ability to fight off infection and general feelings of depression or sadness.

Other research has shown that people with strong social networks have a longer life expectancy and a lower risk for Alzheimer’s disease than those living isolated lives.

These results provide another good reason for people to spend time with family, friends, and co-workers — it protects their health.