Americans are making too many solo dinner reservations.

That was one takeaway from the annual World Happiness Report, which was released on Thursday and showed that the United States had dipped to its lowest slot in the country rankings — 24th — after being ranked as high as 11th in 2012, the first year of the report.

Americans are increasingly miserable, the report says, and it explored a possible indicator: The number of Americans eating alone has risen exponentially this century.

In 2023, according to data from the Bureau of Labor Statistics’s American Time Use Survey, about a quarter of Americans reported eating all of their meals alone the previous day, an increase of 53 percent since 2003.

“The extent to which you share meals is predictive of the social support you have, the pro-social behaviors you exhibit and the trust you have in others,” Jan-Emmanuel De Neve, a University of Oxford professor and an author of the report, said in an interview.

This trend is even more pronounced among young people. For American adults under 25, there has been an 80 percent increase in dining alone among Americans, numbers that Dr. De Neve called “disconcerting.” The survey, which is compiled annually by a consortium of groups including the United Nations and Gallup, offers another data point in the so-called loneliness epidemic, which researchers and officials have said in recent years is becoming a bigger concern, particularly among young men as they spend more and more time on their phones.

Eating alone increases political polarization as well, Dr. De Neve said.

“The fact that we’re increasingly socially isolated means also that we’re not testing our ideas about the world with other people,” he said. “And the more you sit around the table with other people who might have somewhat different views, the more you start moderating your own views. And the increasing lack of social interaction and social isolation as a result, for a lot of people — amplified by echo chambers — makes people more radical.”