People who are socially isolated are more likely to die prematurely, regardless of underlying health problems, according to a study of the elderly British population.

The findings, published online Monday in the Proceedings of the National Academy of Sciences, showed that when mental and physical health conditions were factored out, the lack of social contact still led to early death among 6,500 men and women tracked over seven years.

“They’re dying of the usual causes, but isolation has a strong influence,” said an author of the study, Andrew Steptoe, an epidemiologist at University College London.

The study also appeared to diminish the role that subjective feelings of “loneliness,” as opposed to the lack of social contact, may have on a person’s life span. Both lead to higher mortality risks, the study noted, but the effect of feeling lonely diminishes once demographic and health factors are taken into account.

Regardless of the distinction, the study reinforces the need to increase social support for the elderly, even as it adds to debate over the intertwined effects of social contact and feelings of loneliness in old age. A similar look at retired Americans in 2012 reinforced multiple studies that link loneliness to numerous illnesses, including heart trouble and high blood pressure.

People living alone account for more than a quarter of U.S. households, and the proportion of Americans who said they had no one to talk to about important matters grew from 10 percent in 1985 to 25 percent in 2004, according to authors of the British study. A 2010 European survey showed that more than a quarter of Europeans age 50 and older reported that they met friends, colleagues or family less than once a month.

Separating the effects of loneliness from those of isolation, however, has not been easy for those who study rates of illness and death. While isolation can be measured directly — by how many friends you have or how often you have contact with family — loneliness is more subjective, measured through survey questions about whether social needs and expectations are being met.

Confusing the picture are studies that show loneliness leading to poor health, including higher blood pressure, heightened reaction to stress and altered immune responses, all of which can lead to higher mortality risk.

“Unfortunately in our study, we can’t tell which comes first,” Steptoe said. “We did know that lonely people did have more illnesses.”

Last year’s report on loneliness, based on the U.S. Health and Retirement Study, showed that loneliness appeared to increase mortality risk over six years, an association that could not be attributed to social relationships or health behaviors, such as smoking and drinking.

Isolation may encourage poor lifestyle choices such as smoking, inactivity and unhealthy diets, which factor into mortality rates, said John Cacioppo, director of the Center for Cognitive and Social Neuroscience at the University of Chicago, an author of the 2012 study. He suggested that the British tradition of a “stiff upper lip” may mean Britons who live alone “are less likely to admit to feeling lonely than are residents of the U.S.”