(CNN) - Couples are having less sex than in the previous two decades, new UK research says -- but the number of people wanting more is rising.
A survey found that British people who are married or living with a partner are having sex less often, driving an overall decline in sex within UK society. People over the age of 25 are also having less sex, while more than half of British women and almost two-thirds of men admitted wanting more.
But the general declines did not apply as much to single people, and men under the age of 25 bucked the societal trend and did not report a dropoff in their sex lives. Only 43.4% of single men reported no sex in the previous month in 2012, compared with 50.3% in 1991.
Researchers at the London School of Hygiene and Tropical Medicine analyzed data on more than 34,000 people aged 16 to 44 who had completed the National Survey of Sexual Attitudes and Lifestyles in 1991, 2001 and 2012. Both opposite-sex and same-sex intercourse were included.
There was a significant increase in people overall reporting not having had sex in the previous month between 2001 and 2012; for men, the number jumped from 26% to 29.2%, and for women, it rose from 23% to 29.3%.
Fewer than 1 in 6 people overall reported having sex 10 times or more in the previous month in 2012, according to the study, published Tuesday in the BMJ. By comparison, just over 1 in 5 said they'd had sex 10 or more times in 2001.
Married or cohabiting couples were having slightly more sex in 2001 than in 1991 but less in 2012 than in either of the previous years surveyed.
The findings are UK-specific and do not imply a cause behind the trends, but the overall findings match those in other countries, including the United States, the researchers say.
A 2017 study published in the Archives of Sexual Behavior found that American adults had sex about nine fewer times per year in the early 2010s than they did in the late 1990s.
It's not clear what's behind the dip, but there are plenty of theories -- with some noting that people are having children later in life, which may make them too tired for sex.
"Several factors are likely to explain this decline, but one may be the sheer pace of modern life," Kaye Wellings, professor of sexual and reproductive health at the London School of Hygiene and Tropical Medicine and the study's lead author, said in a news release.
"It is interesting that those most affected are in mid-life, the group often referred to as the 'u-bend' or 'sandwich' generation," she added. "These are the cohorts of men and women who, having started their families at older ages than previous generations, are often juggling childcare, work and responsibilities to parents who are getting older.
"Most people believe that others have more regular sex than they do themselves," Wellings added. "Many people are likely to find it reassuring that they are not out of line."
A number of health benefits have been linked to regular sex, including reduced stress, improved heart health and better sleep.
One study of 20 young healthy couples found that they burned an average of 85 calories for each half-hour romp. Men burned more than women, at about 100 calories versus 69.
CNN's Sandee LaMotte contributed to this report.
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