Is loneliness a silent killer? Things like obesity and smoking are well established and clear contributors to the risk of premature mortality, but according to a new study, the impacts of chronic social isolation may pose a similar threat.

A string of studies over the years have explored the negative health effects of ongoing loneliness. These have linked social isolation to diminished sleep quality, inflammation and increased morbidity. A 2010 paper found that its influence on the risk of early death to be comparable to smoking and alcohol consumption.

And loneliness seems to be on the rise. In 2010, the American Association of Retired Persons conducted a so-called Loneliness Study, using the most recent census data to gauge loneliness among the US population. It found more than a quarter of the nation lived alone, more than half the population was unmarried and, compared to the previous census, marriage rates and children per household had both declined.

"These trends suggest that Americans are becoming less socially connected and experiencing more loneliness," says Brigham Young University's Julianne Holt-Lunstad, who led the new study.

Holt-Lunstad and her team pored over the data from two meta-analyses. The first of those was built on 148 studies involving more than 300,000 subjects, finding that a greater social connection was linked with a 50 percent reduced risk of early death.

The other was made up of 70 studies involving more than 3.4 million subjects from North America, Australia, Asia and Europe, and looked at the impact social isolation, loneliness and living alone have on mortality. The team found that these three factors had a significant impact on the risk of premature death, placing it on par with, or even exceeding, other well-known risk factors like obesity.

According to the researchers, pumping resources into social skills training in schools and encouraging doctors to take social connectedness into account as part of regular medical screening would be a good step forward. They also suggest folks should prepare for retirement in a social sense as well as a financial sense, and that places like recreation centers and community gardens should be designed to include social spaces for sharing and interaction.

"There is robust evidence that social isolation and loneliness significantly increase risk for premature mortality, and the magnitude of the risk exceeds that of many leading health indicators," said Holt-Lunstad. "With an increasing aging population, the effect on public health is only anticipated to increase. Indeed, many nations around the world now suggest we are facing a 'loneliness epidemic.' The challenge we face now is what can be done about it."

The research was presented at the 125th Annual Convention of the American Psychological Association.