Kim Griswold Holmberg's older daughter worries about her.

"She worries that her old mom spends way too much time alone," said Holmberg, 61.

And it's true, she said. "I've been alone for the last 12 years, essentially."

That's how long ago Holmberg divorced, after a 25-year marriage. Now she lives in an apartment in Plymouth — usually alone, although her younger daughter, 25, is living there temporarily. Her other daughter lives in Vietnam, so they get together only once a year or so.

Holmberg recently broke off a 12-year relationship with a man in Duluth — a long-distance relationship that left her alone much of the time. Most of her friends are married and busy with other things. Even at work, Holmberg spends whole days alone, sitting in model homes as a representative for a builder, waiting for the occasional drop-in visitor.

Holmberg makes an effort not to dwell on loneliness.

"I know a lot of people my age suffer from varying degrees of depression because of it," she said. "It does become a mind-over-matter kind of thing."

Depression is one of the most obvious signs of loneliness. But as researchers increasingly investigate the health effects of social isolation, they've linked it to a host of emotional, physical and cognitive problems.

Though not widely recognized by the public or even many health organizations, social isolation is a serious health threat — comparable to smoking 15 cigarettes a day, said Lisa Marsh Ryerson, president of the AARP Foundation.

"Prolonged isolation puts millions of people 50 and up at risk of diminished health," Ryerson said, speaking at the annual meeting of the Gerontological Society of America last fall.

Researchers have found associations between social isolation and a long list of ailments, including dementia, heart disease, stroke, diminished immunity, disrupted sleep, high blood pressure — even increased chance of death. A 2010 study found that people with adequate social relationships have a 50 percent greater likelihood of survival compared with those with insufficient relationships. Another study found that lack of social engagement increases the risk of suicide.

Loneliness can strike at any life stage, of course. But the years of midlife and beyond bring events that can trigger or increase it: divorce, widowhood, children leaving home, friends' deaths, driving restrictions, mobility, hearing or vision limitations and other health problems. People who live in rural areas, belong to marginalized communities or don't speak fluent English are at greater risk. As the overall population ages, loneliness threatens to become epidemic.

Americans once commonly lived with or near their extended families, letting people of different generations help one another. But in recent decades, the culture has become more geographically mobile. Families are scattered around the country or world. Few live in multigenerational households. Meanwhile, membership in traditional social organizations, such as churches and civic groups, has declined.

"A majority of the seniors we see are socially isolated and have loneliness and medical issues related to it," said Joel Theisen, founder and CEO of Lifesprk, an Edina-based organization that provides services for seniors.

"I think, unfortunately, we have isolation by design. Even though we don't want to call it that, we still institutionalize and isolate [older people]. We haven't pulled our families closer together; we've pushed them further apart."

Traditionally, older people have played an important part in families, offering help and knowledge, he said. "It's a symbiotic relationship we've basically butchered."

In an AARP survey of Americans older than 45, the percentage who said they were lonely had doubled since the 1980s. Up to 40 percent now report feeling lonely.

An individual's degree of loneliness can be hard to assess. For one thing, it's subjective — not everyone who lives alone feels lonely. And it carries a stigma; while Holmberg said she has no problem discussing her own feelings, she has lonely friends who won't talk about theirs. Admitting to loneliness feels tantamount to admitting social weakness, unlikability or failure at friendship and love.

And even if a doctor could diagnose loneliness, a physician can offer few solutions beyond medication to treat the depression, Theisen said.

In Minnesota, more than 250,000 people over 60 live alone. "Minnesota nice" — a term sometimes used ironically to indicate residents' superficial friendliness but reticence about forming closer bonds with strangers — may exacerbate isolation.

"This 'Minnesota nice' thing — when will we see it? 'Cause it hasn't happened so far," said Holmberg, who was born and raised here.

Several years ago, Britain began devoting public funds and national attention to combat loneliness, launching programs through local and national governments. In this country, where about one in three people older than 65 (and half over 85) live alone, organized efforts are more recent.

But social service agencies throughout the Upper Midwest have begun hosting parties, delivering home-cooked meals and visiting senior centers. Some programs match older people with younger or peer volunteers. The National Association of Area Agencies on Aging (n4a.org) and the AARP are collaborating nationwide to help seniors assess their risk of isolation and connect them with services. The association has published a brochure offering resources and suggestions for staying socially active: calling friends to get together, taking a class, volunteering for a cause, checking out faith-based organizations and their group events.

For those who want more intensive contact with others, programs are popping up that attempt to mitigate isolation through shared housing arrangements. Some individuals are finding roommates or creating cohousing communities. In Minneapolis, a new program called Vibrante offers a house on Lake Nokomis designed for four older women to share (see page 12). And several groups are working to launch cohousing communities — developments where people occupy separate homes but share common spaces, meals and maintenance chores — to join the existing 25-year-old cohousing community in St. Louis Park (page 13).

Others turn to social media. For Holmberg, the dating website Match.com has been a useful tool. She hasn't found "the one" yet, but "in the meantime, I've been out and about, and I've had some amazing experiences."

Then there's Facebook. Use of the social-networking site has been correlated with loneliness, but it's hard to say whether seeing friends' posts makes people feel lonely or lonely people are drawn to the site for virtual companionship. For Holmberg, it's definitely the latter. "Facebook, to me, is like my family," she said.

This article was written with support from the Journalists in Aging Fellowships, a program of New America Media and the Gerontological Society of America, sponsored by the Retirement Research Foundation.

Katy Read • 612-673-4583