More than a third of adults describe themselves as lonely, with people in their 40s suffering the most, a study has suggested.
Middle aged people were most likely to report feeling lonely
Interviews with almost 1,300 people aged above 18 in Australia focused on feelings of loneliness.
Lowest loneliness levels were seen in teens and the over 50s, the Journal of Clinical Nursing study found
But a UK psychologist said loneliness was not always negative and some people positively chose a solitary existence.
The survey found people with strong religious beliefs were less likely to be lonely, whatever their age.
Women were more likely to have religious beliefs and the research found that, overall, they were less likely to report feeling lonely.
And loneliness was more common in people who were unemployed, compared to those who were retired.
No links were found by the researchers between how long someone had lived in their current community and how lonely they said they were.
But household income had a strong effect, with people in poorer households more likely to be lonely.
Professor William Lauder, of the University of Dundee in Scotland - who worked on the Australian study, said: "Understanding what makes people lonely is very important as loneliness can increase the risk of health conditions such as heart disease and depression, and other problems such as domestic violence.
"One of the most interesting findings of this study is that it challenges the belief that retirement is linked to diminished social contacts and that people get lonelier as they get older."
He added: "Tackling loneliness is very important as it is a very common and potentially health-threatening phenomenon.
"Previous research has shown that, health-wise, it carries a similar level of risk to obesity.
"We hope that this study will provide health professionals and others with further insight into the causes of loneliness, and support efforts to reduce health issues caused by the problem."
But Dr Arthur Cassidy, a social psychologist at the Belfast Institute, cautioned against seeing loneliness as a universally negative thing.
"Loneliness is a social construct.
"There are people who choose to live a solitary existence.
"And people, particularly in their 30s and 40s, may have had negative experiences, such as bad relationships, or may just feel they can't relate to society."