More than a third of adults say they are lonely, especially people in their 40s, a new study shows.

U.K. and Australian researchers conducted 30-minute phone interviews with 1,289 adults in the state of Central Queensland, in Australia.

They found that 35 percent of the respondents said they were lonely. People aged 50 and older had the lowest levels of loneliness. Levels of loneliness began to rise at age 20 and peaked between the ages of 40 and 49.

People with strong religious beliefs were less likely to be lonely than people who had no such beliefs. Women were more likely to have strong religious beliefs, which may explain why women reported lower levels of loneliness than men, the researchers said.

Retired people were less likely than unemployed people to be lonely, and there was a link between household income and loneliness -- people with lower incomes reported higher levels of loneliness.

The researchers found no significant association between loneliness and how long a person lived in their current community.

"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," researcher Professor William Lauder, of the University of Dundee in Scotland, said in a prepared statement.

"One of the most interesting findings in 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," Lauder said.