Sweden is launching a three-year official study of its citizens' sex lives - the first for 20 years.

Health Minister Gabriel Wikstrom said sexual health policy should be guided not just by the problems, but also by the pleasurable aspects of sex.

Surveys done by tabloid newspapers suggest Swedes are having less sex, he wrote in the daily Dagens Nyheter. The new study should find out if that is true, and if so why, he said.

Stress could be a problem, he said.

The study will be conducted by Sweden's Public Health Agency, with the final report expected in June 2019.

Mr Wikstrom said it was "paradoxical that, while our whole society seems permeated by sex, in everything from advertising and social media to much of daily life, the topic is still shrouded by shame... and absent from the political debate".

Focusing on problems such as venereal disease, unwanted pregnancies and rape, to the exclusion of positive sexual experiences, risked distorting health policy, he said.

"How can we change attitudes," he asked, "when so many people, from parents and teachers to senior officials, are so obviously uncomfortable when talking about sex?"