Since about 2012, researchers have noticed somewhat of an unusual trend in the United States: Fewer Americans are having sex than they did in previous decades.

“We are seeing pretty marked increases in the share of people who are not having sex frequently — especially in the share of younger adults,” W. Bradford Wilcox, director of the National Marriage Project at the University of Virginia, told TODAY. “We have come to a day that is about 50 years after the sexual revolution and what we are seeing is a decline of sex among young adults. No one, including myself, could have predicted this.”

In a recent story, The Washington Post crunched the numbers from the General Social Survey, which is conducted by NORC at the University of Chicago, about what it called the “Great American Sex Drought,” and noted that 23 percent of adults admitted to not having sex in past year. What’s more, young men, especially those who are living at home and not working, are driving this trend.

“The economic issues are real and significant,” Christine Whelan, director of Money, Relationships and Equality Initiative in the School of Human Ecology at the University of Wisconsin, Madison, told TODAY. “Increasingly what both men and women are looking for it a good financial prospect.”

While this "sex recession" seems to have the biggest impact on economically disadvantaged people, the experts have identified several reasons why people generally are having less sex. Most notably, people are delaying marriage.

“Time spent outside of marriage tends to lead to less sexual activity,” Whelan said. “People who are partnered up in committed long-term relationships have more access to sex and have it more regularly.”

It also appears younger people are less interested in dating and simply don’t try. That could be part of what Wilcox calls “caution culture.”

“For anything that is more risky, including sex, there is an inclination of younger adults to approach that more carefully than was the case 30 years ago,” he said.

Whelan believes the obesity epidemic, opioid addiction, aging population and other health factors put a damper on bedroom activity. But researchers also point to increasing reliance on smartphones and screens as another reason.

“Are couples really saying, 'put your phone down I want to have sex'?” Whelan said. “The separate devices really take a toll on intimacy.”

Less sex predicts other trends.

While studies about sex droughts and intimacy recessions cause titillation, examining sexual habits provide insight into Americans' state-of-mind and happiness generally.

“Sex is associated with better wellbeing. We find young adults who have sex at least once a week are more likely to report they are very happy, as opposed to their peers who are not having sex,” Wilcox said.

Whelan agrees.

“These pair bond relationships are central to our wellbeing. Whenever we do something that separates us from these strong positive attachments it can have real negative implications to your overall wellbeing,” she said.

Historically, intimate relationships were measures of achievement.

"If we are less and less able to engage in physical intimacy, then we are moving away from something that is an evolved tendency that actually signals success," she said. "This is not to say you have to have sex to be happy. But sex is associated with healthy relationships and overall wellbeing."

For some, hearing about what happens, or doesn't, in the bedroom is a way to measure how normal they are. But the experts agree that Americans' willingness to engage in intimacy tells us more about other trends, including declining birth rate and increasing loneliness. Recent research shows that loneliness can be as damaging to health as excessive drinking or gaining weight.

“We have hundreds of friends online but not having anyone to reach out to in the time of need,” Whelan said. “Are we increasingly unable to form relationships?”