The Backstreet Boys asked and science answered: Being lonely means an increased risk for coronary heart disease.

That loneliness and social isolation could be risk factors for disease and death is an idea that has been brewing in the scientific community for some time now. In 2006, a JAMA study found social isolation in childhood may increase the risk for cardiovascular disease in adulthood. A couple years later, at Ohio State University, researchers found that social isolation, in mice anyway, makes strokes more deadly. The team conducted a second study in 2010 and found having no contact with friends or family can worsen the brain damages caused by a heart attack. Then, in 2015, Brigham Young University put it plainly: The prescription for living longer is to spend less time alone.

While experts have started to suspect loneliness negatively affects heart health, new research published today in the journal Heart argues that the topic has yet to be widely studied. Study co-author Nicole Valtorta, research fellow at the University of York, told Medical Daily that the existing literature her team reviewed focused more on how weakened social relationships increase risk for mortality overall. “It didn’t tell us if people who felt lonely were at increased risk of developing disease once they were in ill health,” she said. “We wanted to bring together the information of all the studies we could find and see what comes of it.”

Valtorta and her colleagues at York and the universities of Liverpool and Newcastle combed through 1 6 research databases for studies that investigated new cases of heart disease and stroke at the individual level as a function of loneliness, social isolation, or both. To measure for social aspects, the team put in place criteria for each term: Loneliness is the negative feeling a person has when she thinks her relationships are deficient, Valtorta said. A lonely person could be surrounded by lots of people and still be unhappy. Social isolation, on the other hand, is when a person is not in contact with anyone, including his friends and family.

The researchers chose 23 studies for analysis, ultimately including more than 181,000 adults. And the results showed that loneliness and social isolation was associated with a 29 percent increased risk of a heart attack or episode of chest pain and a 32 percent heightened risk of having a stroke. The two had a greater effect on heart health than general anxiety and job stress, the team wrote.

That said, this was an observational study, meaning Valtorta can’t rule out potential, unmeasured factors or reverse causation. For example, is it feeling like you’re alone that hurts your heart or is it an undiagnosed disease that promotes social isolation? At this point, it would be unethical to lean any one way, Valtorta said, but she does believe her findings are enough to start informing clinical practice.

“We need more studies, but little by little the evidence is growing,” she said.

In an accompanying editorial, doctors Julianne Holt-Lunstad and Timothy Smith of Brigham Young University, the authors of the 2015 study that prescribed spending less time alone, argue that Valtorta’s study is the latest to show that “loneliness and isolation bolster the already robust evidence documenting that social connections significantly predict morbidity and mortality, supporting the case for inclusion as a risk factor for cardiovascular disease.”

The World Health Organization does list social support networks as one of its determinants of health, as do other major organizations specific to heart disease. But this inclusion should extend to medical education, individual risk assessment, and the guidelines and policies applied to populations and the delivery of health services, the doctors wrote. "Given projected increases in levels of social isolation and loneliness in Europe and North America, medical science needs to squarely address the ramifications for physical health.”

Holt-Lunstad told Medical Daily that experts have been worried about the implications of reduced social network size in both the United Kingdom and United States. The average size of Americans’ core discussions networks has declined since 1985, according to the Pew Internet Personal Networks and Community survey : The average size dropped by about one-third, or a loss of approximately one friend, a small to modest change. And in 2014, the Independent Age and the International Longevity Center predicted that social isolation among the elderly population could reach epidemic proportions by 2030. Young people are at risk too: New Scientist has written that adults ages 18 to 24 report feeling more lonely than they have in the past.

Some sociologist believe new technology, like the internet and social media, have advanced the trend, while the Pew survey found that internet users were 55 percent more likely to talk to people they weren’t related to and that in-person contact remains Americans’ dominant means of communication.

Which leads back to Valtorta’s initial idea: We simply need more research.

“I was surprised by the scarcity of the data. We don’t really have much to refer to,” she said. “We compared people who are lonely to people who weren’t lonely, and people who were socially isolated and not.” But her study doesn’t have all the answers, she added. “It doesn’t tell us: if you’re lonely, and you try to change that, will it benefit your health?”

Sources: Valtorta NK et al. Loneliness and Social Isolation As Risk Factors For Coronary Heart Disease and Stroke: Systematic Review and Meta-Analysis of Longitudinal Observational Studies. Heart. 2016.

Holt-Lunstad J, Smith TB. Loneliness and Social Isolation As Risk Factors For CVD: implications For Evidence-Based Patient Care and Scientific Inquiry. Heart. 2016.