Social Isolation Growing in U.S., Study Says

"For most of the 20th century, Americans were becoming more connected with family and friends, and there was more giving of blood and money, and all of those trend lines turn sharply in the middle '60s and have gone in the other direction ever since," he said.

Americans go on 60 percent fewer picnics today and families eat dinner together 40 percent less often compared with 1965, he said. They are less likely to meet at clubs or go bowling in groups. Putnam has estimated that every 10-minute increase in commutes makes it 10 percent less likely that people will establish and maintain close social ties.

Television is a big part of the problem, he contends. Whereas 5 percent of U.S. households in 1950 owned television sets, 95 percent did a decade later.

But University of Toronto sociologist Barry Wellman questioned whether the study's focus on intimate ties means that social ties in general are fraying. He said people's overall ties are actually growing, compared with previous decades, thanks in part to the Internet. Wellman has calculated that the average person today has about 250 ties with friends and relatives.

Wellman praised the quality of the new study and said its results are surprising, but he said it does not address how core ties change in the context of other relationships.

"I don't see this as the end of the world but part of a larger puzzle," he said. "My guess is people only have so much energy, and right now they are switching around a number of networks. . . . We are getting a division of labor in relationships. Some people give emotional aid, some people give financial aid."

Putnam and Smith-Lovin said Americans may be well advised to consciously build more relationships. But they also said social institutions and social-policy makers need to pay more attention.

"The current structure of workplace regulations assumes everyone works from 9 to 5, five days a week," Putnam said. "If we gave people much more flexibility in their work life, they would use that time to spend more time with their aging mom or best friend."