Lynn Smith-Lovin was listening in the back seat of a taxi when a woman called the radio talk-show hosts to confess her affairs with a new boyfriend and a not-yet-former husband. The hosts, in their best therapeutic voices, offered their on-air opinion, "Give me an S, give me an L, give me a U." You can spell the rest.

It was the sort of exchange that would leave most of us wondering why anyone would share her intimate life story with a radio host. Didn't she have anyone else to talk with? Smith-Lovin may have been the only one in the audience with an answer to that question: Maybe not.

The Duke sociologist is co-author of one of those blockbuster studies that make us look at ourselves. This one is labeled "Social Isolation in America," although it could as easily have been labeled "Friendless in America."

A face-to-face study of 1,467 adults turned up some disheartening news. One-fourth of all Americans report that they have nobody to talk to about "important matters." Another quarter report they are just one person away from nobody.

But this was the most startling fact. The study is a replica of one done 20 years ago. In only two decades, from 1985 to 2004, the number of people who have no one to talk to has doubled. And the number of confidants of the average American has gone down from three to two.

Imagine if some other piece of the social safety net had frayed that furiously. Imagine if income had gone down by a third, or divorce doubled or the medical system halved. We would be setting up commissions and organizing rallies.

The people you are closest to form your own informal safety net. They're the ones who see you through a life crisis, lend you their spare bedroom or pick up your kids at school in a pinch. Social isolation is as big a risk factor for premature death as smoking. Robert Putnam has already chronicled the erosion of the ties that bind us as a community and a nation in "Bowling Alone." But we've paid less attention to "coping alone" or "suffering alone."

Not everything in the study was gloomy. Deep in the data is the suggestion that families — husbands and wives, parents and adult children — may be closer. Spouses who call each other "my best friend" may be right. We may have fewer intimates, but we're more intimate with them. On average, we see them more than once a week and have known them seven years.

Nevertheless, the big news is that circles have tightened, shrunk and gone nuclear. As Smith-Lovin says, "Literally nothing takes the place of family." The greatest loss has been in neighbors and friends who will provide help, support, advice and connections to a wider world.

There is no shortage of speculation about why our circle of friends is eroding. The usual suspect is the time crunch. It's knocked friendship off the balancing beam of life as we attend to work and family. It's left less time for the groups and associations that bind us.

But in the past 20 years, technology has changed the way we use our "relationship time." Walk along any city street and people talking on cell phones are more common than pigeons. Go into Starbucks and a third of the customers are having coffee dates with their laptops.

"It could be that talking to people close to us on cell phones has caused our social circle to shrink," says Smith-Lovin. It could be that we are both increasingly in-touch and isolated.

It's become easier to keep extensive relationships over time and distance but harder to build the deep ones in our backyard. In the virtual neighborhood, how many have substituted e-mail for intimacy, contacts for confidants and Facebook for face to face?

A few years ago, when my friend Patricia O'Brien and I wrote a book on the power of friendship in women's lives, we noted that there was no official status for friends, no pro-friendship movement, no cultural or political support system for friends. Yet this voluntary relationship can be the most sustaining one of life.

Now we are living in smaller, tighter circles. We are 10 degrees of separation from each other and one or two people away from loneliness. And many now "outsource" intimacy from friends to professional therapists and, gawd help us, talk shows.

Whom can we talk to about "important matters"? Whom can we count on? As we search for tools to repair this frayed safety net, Americans can take poor, paradoxical comfort from the fact that if you are feeling isolated, you are not alone.

Ellen Goodman is a columnist for The Boston Globe. Reach her at ellengoodman@globe.com.