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When Daniel Russell and his colleagues at UCLA set out to create a standardized way to measure people’s loneliness in 1978, what they came up with was arguably the least fun 20-item questionnaire in history. On a four-point scale from “never” to “often,” it asked individuals: How often did they feel they had no one to turn to or talk to? How often did they feel their relationships with others were not meaningful? How often did they feel left out?

It was probably not the most painless way to learn about the inner lives of people who reported feeling bummed-out and alone. But over the course of 40 years, the UCLA Loneliness Scale has become a valuable tool in studying what’s now being called an epidemic in some Western countries. Case in point: The United Kingdom last week announced the creation of a Minister for Loneliness role within its government. Tracey Crouch, the former minister for Sport and Civil Society, will now be tasked with carrying out the prescriptions of the Jo Cox Commission on Loneliness (named for a member of Parliament who was murdered in 2016), which released a report last year declaring that over 9 million British adults reported being “often or always lonely,” approximately 15 to 20 percent of the adult population. For comparison, while research on loneliness among all adults in the U.S. is scarce, a 2012 study found that between 20 and 43 percent of American adults over age 60 experienced “frequent or intense” loneliness.

When researchers study loneliness, they tend to define it as “the perceived discrepancy between one’s desired level of social connection and their actual level of social connection,” says Brigham Young University psychology and neuroscience professor Julianne Holt-Lunstad. Some people who are socially isolated don’t necessarily feel lonely, and some people who are lonely are surrounded by people who make them feel more alienated, not less.

But 9 million lonely people probably aren’t just a damper on the national morale; they’re likely to be a strain on national productivity and health-care systems, too. The bodies of lonely people are markedly different from the bodies of non-lonely people. Prolonged loneliness, Holt-Lunstad says, “can put one at risk for chronic health conditions, exacerbate various health conditions, and ultimately put us at increased risk for premature mortality.” The bodies of lonely people are more likely to have:

High blood pressure and cardiovascular disease. Loneliness, it turns out, is bad for both your figurative heart and your literal one. As Holt-Lunstad points out, feeling lonely can make our environments feel just plain unsafe or unfriendly, which — as most of us have gleaned just by being alive and sometimes feeling acutely, anxiously alone — can make our heart rates faster and our blood pressures go up.

The bodies of lonely people are markedly different from the bodies of non-lonely people.

Those cardiovascular effects are frequently attributed to cortisol, the “stress hormone,” and studies of loneliness have shown lonely people have consistently elevated levels of cortisol. Which can contribute to other sorts of problems: “Chronic high blood pressure can lead to hypertension,” Holt-Lunstad says, “and hypertension is a risk factor for heart disease.”

These effects can accumulate over time, too. A 2002 National Institutes of Health study showed that lonely participants’ cardiovascular systems responded less acutely to laboratory stress tests, but only because their cardiovascular systems were more constricted and pressurized in general. And according to one NIH review of the physiological effects of loneliness, consistently feeling rejected or lonely early in life is a good predictor of high blood pressure in young adulthood — and of more exaggerated high blood pressure in middle age.

Reduced immunity. Lonely people can also be more susceptible to illness. A 2005 study of 83 healthy first-semester college freshmen found that those who reported feeling lonely also responded more poorly to getting the flu vaccine; their bodies didn’t produce antibodies quite as well as those of non-lonely people. “Those with both high levels of loneliness and a small social network had the lowest antibody response,” the study authors add.

Why does this happen? One pathway researchers have identified is that stress hormones, in conjunction with other hormones and peptides secreted from the brain, “talk” to specific parts of the body’s white blood cells, affecting their distribution and function.

Inflammation. Lonely people are especially susceptible to chronic inflammation, which is considered a key component in a wide range of health maladies. Heart disease, Alzheimer’s, and potentially even certain cancers can stem from it; so can rheumatoid arthritis, clogged arteries, and periodontitis.

As UCLA genomics researcher Steve Cole explained to NPR in 2015, he’d found in his research that “when people felt lonesome, they had significantly higher levels of norepinephrine,” the hormone that shuts down viral defense but escalates production of certain white blood cells “coursing through their blood.” At the same time, NPR writes, lonely people develop a genetic immunity to the inflammation-curbing properties of the “stress hormone” cortisol, so the defensive inflammation response increases.

Poor sleep. When the NIH conducted its loneliness study in 2002, researchers found in their labs what stressed-out, lonesome-feeling people have found in their bedrooms for centuries: Lonely people took longer to fall asleep than non-lonely people, slept for a shorter time, and had “greater daytime dysfunction.”

And, of course, whatever damage loneliness itself doesn’t do to you physically, the sleep loss it causes will. Sleep-restriction studies have found sleep-deprived people are more likely to suffer from lowered glucose tolerance (which sometimes leads to type 2 diabetes) and elevated stress hormone levels in the evenings. Plus, the authors of the 2002 NIH study add, “If individuals are lonely chronically, it is conceivable that the effects of impaired sleep diminish nightly restorative processes and the overall resilience of lonely individuals.” These findings also suggest that sleep loss can exacerbate those effects in older age.

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So how, exactly, would a Minister for Loneliness be able to help a country full of people feeling lonesome? The Cox Commission endorses measures that aim to both find and engage with lonely people where they live and draw them out into community gatherings — like citywide “Door Knock” events and “The Great Get-Together” weekends organized by county councils. When I asked Holt-Lunstad whether one could really expect these kinds of programs to work, her answer surprised me.

“People ask me, ‘What are we supposed to do, make people go around and hug each other?’” she says. But we have “good evidence,” Holt-Lunstad says, that a loneliness epidemic is developing in the United States, too — and the U.S. should consider following Britain’s lead in making loneliness a public-health priority.

Holt-Lunstad testified before the U.S. Senate Committee on Aging last spring to propose some measures aimed at doing just that. For example, she helped usher in new legislation designed to make hearing aids more affordable, since hearing loss is a risk factor for social isolation and loneliness, especially for older adults. “If you can’t hear, it’s hard to be part of a conversation,” she says. “It’s easy to start to withdraw and disconnect from others.” Holt-Lunstad has also endorsed programs like Oprah Winfrey’s “Just Say Hello” campaign and the AARP’s efforts to combat social isolation, but cautions that meaningful public health benefits will emerge only when the measures taken are firmly rooted in research findings.

Additionally, Holt-Lunstad says, assessing the risk of loneliness and loneliness-related health problems should be part of medical training; doctors should communicate to patients how to prevent loneliness and encourage them to take it seriously as part of a healthy lifestyle, “just like you would take sleep, exercise, diet, all of these kinds of things seriously.”

But it’s not just the elderly who need loneliness intervention, she says. She thinks social education should be taught in schools the way physical education is. In K–12 curriculums, it’d be beneficial to educate kids on “not only why it’s important for our health but what good relationships look like. How to be a good friend,” she says. “Just like being physically active, we need to be socially active.”

Research on young people’s loneliness isn’t abundant. But what does exist suggests loneliness might not go away anytime soon as a health crisis: A UCLA Berkeley study published last year found that even though adults between 21 and 30 had larger social networks, they reported twice as many days spent feeling lonely or socially isolated than adults between 50 and 70.