Lonely people who catch the common cold suffer from the worst symptoms, researchers have found.
Scientists infected more than 150 people with the common cold and quarantined them in hotel rooms alone for five days. They found those who said they were lonely reported the most severe symptoms, including chills, runny nose, sore throat and headaches reported the Daily Mail.
It is known that the lonely are more likely to die early or develop heart disease, but this is the first study to show they suffer more from common bugs.
Those most at risk are not people with the fewest friends, but those who feel lonely due to a lack of people close to them.
The US researchers did not look at the reason why they had worse colds, but previous studies show loneliness over-stimulates white blood cells and reduces antiviral proteins, which can affect the immune system.
Two-thirds of British adults feel lonely often, always or sometimes, according to surveys.
Lead author Angie LeRoy, from Rice University in Houston, said: "Previous research has shown that different psycho-social factors like feeling rejected or feeling left out or not having strong social bonds with other people do make people feel worse physically, mentally and emotionally.
"Millions of people miss work each year because of the common cold. And that has to do with how they feel, not necessarily with how much they're blowing their noses."
About 27 million days of work are lost in the UK every year because of the common cold.
The study by Rice, Houston and Delaware universities found that while lonely people are not more likely to catch a cold, they will suffer more badly.
The researchers took 159 people, mostly middle-aged, and gave them cold-inducing nasal drops before monitoring their health. The three-quarters who fell ill were asked for their daily symptoms. The lonely people were identified using questions such as: 'In general, how often do you feel isolated from others?"
These people felt significantly worse after catching a cold. The study states: "Individuals with small social networks may be socially isolated, but not necessarily lonely.
"Likewise, lonely people can have small or large social networks - loneliness relies on the perception of the quality of one's social relationships."
The research, published in the journal Health Psychology, says loneliness could make colds worse because people do not get as much sleep, making them more vulnerable to being sick.