Shaheen Shivji was happier in Kabul. There were bombs going off outside the compound where she worked for a development agency, but she preferred life in the Afghan capital to the one she had at home in Abbotsford, B.C., for one simple reason: She wasn't lonely.

"For the first time in my adult life, I didn't feel isolated," she says. "I felt socially connected, I was with like-minded people. I was doing something important to better the world."

Afghanistan became too dangerous and, after a year, Ms. Shivji moved back to B.C., where she lives with her parents and works as a communications manager for local government. She has one friend she texts regularly, but otherwise her old university crowd has married and drifted away. She yearns for simple connection in her life, to meet a friend regularly for coffee or a movie, to occasionally feel a kind hand on her arm. Work is her main source of satisfaction.

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The toll of her loneliness isn't just emotional. At 44, she feels tired, distracted, unable to concentrate. It's an effort to get to the gym. Over the phone, her voice becomes strained. "I just feel sad most of the time."

Ms. Shivji feels like she's on the outside looking in and, in that sense, she's not alone.

In the West, we live faster, higher in the air, farther from our workplaces, and more singly than at any time in the past. Social scientists will be struggling to understand the consequences of these transformations for decades to come, but one thing is clear: Loneliness is our baggage, a huge and largely unacknowledged cultural failing.

In Vancouver, residents recently listed social isolation as their most pressing concern. More Canadians than ever live alone, and almost one-quarter describe themselves as lonely. In the United States, two studies showed that 40 per cent of people say they're lonely, a figure that has doubled in 30 years. Britain has a registered charity campaigning to end chronic loneliness, and last month, health secretary Jeremy Hunt gave a speech about the isolated many, calling attention to "a forgotten million who live amongst us ignored, to our national shame."

It is the great irony of our age that we have never been better connected, or more adrift.

The issue isn't just social, it's a public-health crisis in waiting. If you suffer from chronic loneliness, you run the risk of illness, and premature death.

"This is a bigger problem than we realize," says Ami Rokach, a psychologist and lecturer at York University in Toronto, who has been researching the subject for more than three decades.

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"Loneliness has been linked to depression, anxiety, interpersonal hostility, increased vulnerability to health problems, and even to suicide."

And yet loneliness is the longing that dare not speak its name. Keenly aware that isolation carries with it the whiff of failure, Ms. Shivji was reticent to be identified for this story. Inside every lonely adult is a kid eating lunch by herself on a bench.

Says Prof. Rokach, "There is such a stigma about it. People will talk about having depression or even schizophrenia, but … I've been practicing for more than 30 years, and never has anyone come to me and said, 'I feel lonely.' But then they start talking and it comes out."

This is why David Sutcliffe has launched a bit of a one-man shame-reduction campaign. Mr. Sutcliffe is no one's idea of a social outcast: He's a handsome and accomplished actor, once a regular on Gilmore Girls and now the star of CBC-TV's Cracked, about a detective with mental-health issues.

And yet, for his whole life, he has been plagued by a profound sense of isolation. He stayed inside. He self-medicated. When he was in his mid-twenties, his therapist asked, "Have you always been this lonely?" He burst into tears.

There was a point when Mr. Sutcliffe, now 44, felt so alone that he would get a massage just to feel another person's touch. He has a friend in Los Angeles who runs a "hugging practice," offering long embraces to people who have no one to comfort them. "At first it seemed like a wacky California idea," he says, "but now it makes complete sense."

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It was difficult for Mr. Sutcliffe to watch himself on screen during the first season of Cracked: "I saw a very lonely guy, and I know that pain wasn't the character; it was me. But I was glad to put it out there, because it's important for people to know they're not alone. We're all struggling."

We are, indeed, but why? Chronic loneliness has roots that are both internal and external, a combination of genes and social circumstance, but something is making it worse. Blame the garage-door opener, which keeps neighbours from seeing each other at the end of the day, or our fetish for roads over parks, or the bright forest of condo towers that bloom on our city's skylines.

Or blame an increasingly self-absorbed society, as John Cacioppo does. Prof. Cacioppo, the leading authority on the health effects of loneliness, is director of the University of Chicago's Center for Cognitive and Social Neuroscience. "One of the things we've seen is a movement away from a concern for others," he says in a phone interview. "Economics basically says you should be concerned about your own short-term interests. There's more division in society, more segmentation; there's less identity with a national or global persona, but rather on the family or the individual. People aren't as loyal to their employers, and employers are certainly not as loyal to their workers."

Loneliness, it turns out, is as bad for your health as smoking, or being obese. The research that Prof. Cacioppo has done with colleagues also adds to the growing body of work that shows how bad loneliness can be for your health. It shows that loneliness suppresses the immune system and cardiovascular function, and increases the amount of stress hormone the body produces. It causes wear and tear on a cellular level, and impairs sleep. As he writes in his book Loneliness, "these changes in physiology are compounded in ways that may be hastening millions of people to an early grave."

His theory, simply, is that we are social animals who function most successfully in a collective; the physical pain and degradation caused by loneliness are a kind of early-warning signal of a failure to connect, the way the pain of a cut finger tells you to fetch a Band-Aid.

A study last year from the University of California at San Francisco showed a clear link between loneliness and serious heart problems and early death in the elderly. Seniors in the study who identified themselves as lonely had a 59-per-cent greater chance of health problems, and a 45-per-cent greater chance of early death.

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Carla Perissinotto, the doctor who led the study, said she once encountered an elderly patient in a hospital emergency ward who seemed to have nothing wrong with her. She soon realized the woman was so lonely that she just wanted someone to talk to.

Older people come to mind first when we think about loneliness. As a 78-year-old woman living alone in a small Ontario city puts it, "I feel like everything is behind me, and that there's nothing to look forward to."

About 20 per cent of older people in this country report feeling lonely, according to a 2012 Statistics Canada report. But that's not the whole picture, because a sense of isolation doesn't arrive with grey hair: In a study of 34,000 Canadian university students, almost two-thirds reported feeling "very lonely" in the past 12 months. More Canadians are living alone than at any other point in history, and half again as many of them (21 per cent) are more likely to report feeling lonely than those who are part of a couple (14 per cent).

Being alone is not the same as being lonely, of course. Plenty of people are happy to sit in their studies, play World of Warcraft and not see another human being for days. The problem arises when the lonely become incapacitated by their situation, losing all sense of how to reconnect, and withdraw even further in a wearying circle. The holiday season, which comes wreathed in idealized depictions of cheery families, is particularly dreaded.

In some cases, isolation is taken to gothic extremes. In Britain, a young woman named Joyce Carol Vincent died and wasn't discovered for three years. Neighbours ignored the strange smell coming from in her apartment and, when her body was finally found, the TV was still on. She became the subject of morbid fascination, and a documentary.

This month, the story of Harold Percival, a British veteran of the Second World War, caused a brief sensation. When he died alone in a nursing home at 99, a Twitter campaign drew hundreds to his funeral. More than a few observers wondered whether the mourners might have been better employed visiting Mr. Percival while he was still alive.

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Does the wired world make us feel even more cut off?

Proponents and detractors of social media can cherry-pick from studies showing that technology makes people feel either more connected, or more isolated. But one this summer from the University of Michigan analyzed subjects' responses to a variety of texted questions during the day, and showed that using Facebook increased feelings of loneliness and alienation: "On the surface," the researchers wrote, "Facebook provides an invaluable resource for fulfilling the basic human need for social connection. Rather than enhancing well-being, however, these findings suggest that Facebook may undermine it."

Talk to enough lonely people and you'll find they have one thing in common: They look at Facebook and Twitter the way a hungry child looks through a window at a family feast and wonders, "Why is everyone having a good time except for me?"

Marci O'Connor, 42, is an anglophone living in the largely French-speaking community of Mont Saint-Hilaire, just south of Montreal, with her husband and two children. She "almost feels guilty" for her feelings of isolation, but years of working alone as a freelance writer have taken their toll, and she's now applying to be a waitress so she'll have more human contact.

She has come to believe that there is no substitute for that contact, even if it's just a smile while delivering a beer. For a while, Ms. O'Connor advised companies on their social-media strategies, but she has become increasingly disenchanted with the online world. "It's so hollow," she says. "You might get a lot of likes or retweets, but it's fragile and meaningless. It's not like I could call any of these people at 3 a.m. and they'd help me with my flooded basement."

Ask Vancouverites what bothers them, and you'd think they might say house prices. Drugs on the street. Not being able to get into the hot new sushi joint. But when the Vancouver Foundation asked that question, it received a gobsmacking response.

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"The biggest issue people had is that they felt lonely, isolated, and unconnected to their communities," says Kevin McCort, president of the community-outreach charity. Last year, the foundation conducted a survey of almost 4,000 Vancouverites and found that one-third of those between 25 and 34 felt "alone more than they would like." Another one-third said they have trouble making friends. Forty per cent of high-rise dwellers felt lonely, almost twice the number (22 per cent) living in detached homes. Crucially, the study found that the loneliest also reported being in poorer health and lacking trust in others.

"Social isolation just may be the greatest environmental hazard of city living," writes Vancouver-based author Charles Montgomery in his new book, Happy City: Transforming Our Lives Through Urban Design. "Worse than noise, pollution, or even crowding." And the way we've built cities – suburbs with no central meeting place, prioritizing the car and the condo tower, passing restrictive zoning bylaws – has made the problem worse, he says in an interview. "If we're concerned about happiness, then social disconnection in Canadian cities is an acute problem."

Mr. Montgomery points to cities that have done things right, from Portland, Ore., turning its intersections into urban piazzas to the community gardens built in disused lofts in Berlin. Research has shown that a varied streetscape will cause people to slow down, and perhaps even exchange a smile or flirtatious glance, and that even a brief exposure to nature – cutting through a park – makes us feel more generous, and more social.

The Vancouver Foundation has another answer: It is giving out grants of $500 to people who will organize a community event that brings strangers together – a knitting circle, an origami workshop, a pumpkin-carving jamboree. Mr. McCort attended one gathering recently, and was struck by an unfamiliar sight: "No one was on their phone, or checking email. There were a hundred people, just talking and making new friends."

On a personal level, being lonely can seem crippling, and saying "just get out and make friends" is like telling an asthmatic to climb Mount Everest. Prof. Cacioppo notes that lonely people will either withdraw into their shells or attempt to soothe their pain by lashing out. The first step, he says, is to recognize and acknowledge painful feelings, and to try to make small advances each day – by smiling at a neighbour, or performing an unexpected kindness for a stranger.

David Sutcliffe says he forces himself to keep a busy social schedule, or he would never leave the house. Group therapy has been a huge help. He also is evangelical about sharing his story, to combat what he calls "society's tranquillity mask" – our tendecy to pretend that everything is swell, even when it isn't. He knows he speaks for those who can't or won't.

"There are a lot of people walking around who feel that they don't fit in, they don't belong. That sense of disconnection is really common. But when you realize that you're like everyone else, not only in your dreams and passions but also in your pain and sadness, there's incredible comfort in that."