By Nick Triggle Health correspondent, BBC News
Money worries and the distractions of social media mean people are having sex
less frequently, researchers say.
A survey of more than 15,000 Britons found those aged 16-44 were having sex
fewer than five times a month.
The figure compared with more than six times a month on the last two occasions
when the official National Survey of Sexual Attitudes and Lifestyles was
carried out, in 1990-91 and 1999-2001.
The study's authors say modern life may be having an impact on libidos.
Dr Cath Mercer, from University College London, said: "People are worried about
their jobs, worried about money. They are not in the mood for sex.
"But we also think modern technologies are behind the trend too. People have
tablets and smartphones and they are taking them into the bedroom, using
Twitter and Facebook, answering emails."
Graph
She also said the survey suggested that couples aged 16 to 44 may be using
online porn as a substitute for sex.
Men polled in 2010 to 2012 reported having sex 4.9 times a month and women 4.8.
In both previous surveys the averages were over six for both sexes both times.
The latest survey, which is carried out every 10 years, also asked older people
about their sex lives.
It found 42% of women and 60% of men aged 65 to 74 had had sex in the past
year.
Nonetheless, they were the age groups having the least sex - 2.3 times a month
for men and 1.4 for women.
Among men, the 25 to 34 age group were having the most sex - 5.4 times a month
- and for women it was the 16 to 24 age group, 5.8 times.
The average woman aged under 44 said they had had 7.7 partners over their
lifetime, while for men it was 11.7.
The survey also asked participants about whether they had paid for sex in the
past five years. Hardly any women had, but 3.6% of men admitted to it.
But the poll - the full details of which have been reported in the Lancet -
also revealed the extent to which people are forced to have sex against their
will.
One in 10 women and one in 70 men said they had experienced it.
However, fewer than half had told anyone about it and even fewer (13% of women
and 8% of men) had reported the crime to the police.