Led by researchers from Rice University in Houston, TX, the study found that people who felt lonely reported worse cold symptoms than individuals who did not feel lonely.

Study co-author Angie LeRoy, a graduate psychology student at Rice University, and colleagues recently reported their results in the journal Health Psychology.

According to a 2016 survey, around 72 percent of people in the United States report feeling lonely. Of these individuals, around 31 percent report feeling lonely at least once a week.

Feeling socially isolated can take its toll on psychological well-being, raising the risk of anxiety and depression, but its effects do not end there.

Loneliness can have serious implications for physical health, too. A study reported by Medical News Today in 2016, for example, associated loneliness with an increased risk of heart disease and stroke.

"Research has shown that loneliness puts people at risk for early death and other physical illnesses," LeRoy notes. "But nothing had been done to look at an acute but temporary illness that we're all vulnerable to - the common cold."

For their study, LeRoy and colleagues investigated how feelings of loneliness might affect the risk of catching the common cold, as well as the severity of cold symptoms.

Quality, not quantity of social networks affects severity of cold symptoms

To reach their findings, the researchers enrolled 159 individuals aged between 18 and 55, of whom around 60 percent were men.

Participants were given nasal drops that induced a cold, before being quarantined in a hotel room for 5 days.

The loneliness of each subject was assessed at study baseline using the Short Loneliness Scale and the Social Network Index. During the 5-day study period, participants were asked to report their symptom severity.

Around 75 percent of participants developed a cold following nasal drop administration.

The team found that the risk of developing a cold was no different between lonely and non-lonely participants.

However, participants who reported feeling lonely at study baseline reported greater severity of cold symptoms than subjects who did not feel lonely. The size of subjects' social networks appeared to have no influence on symptom severity.

"We looked at the quality of people's relationships, not the quantity," says LeRoy. "You can be in a crowded room and feel lonely. That perception is what seems to be important when it comes to cold symptoms."

"We think this is important, particularly because of the economic burden associated with the common cold. Millions of people miss work each year because of it. And that has to do with how they feel, not necessarily with how much they're blowing their noses."

Angie LeRoy

Findings may not be limited to the common cold

The team cites previous studies that have associated feelings of rejection or other psychosocial factors with worse physical and mental health, which may explain the current findings. However, the team says that such an effect is unlikely to be limited to the common cold.

"A predisposition, whether it's physical or mental, can be exaggerated by a subsequent stressor," says study leader Chris Fagundes, a psychologist at Rice University. "In this case, the subsequent stressor is getting sick, but it could be the loss of a loved one, or getting breast cancer, which are subjects we also study."

Fagundes adds that physicians should consider patients' psychological health when assessing them for illness. "It would definitely help them understand the phenomenon when the person comes in sick."