Many older people remain sexually active
More couples over 70 are having sex - and finding it satisfying - than in previous generations, a British Medical Journal survey suggests.
Swedish researchers asked 1,500 older people across a 30-year period about their sex lives.
The number of people saying they had sex increased - as did the number of women reporting having orgasms.
A UK expert said the older people of today grew up in more sexually liberated eras.
Although there are plenty of studies about sexual "problems" associated with old age, there is relatively little research about "normal" sexual behaviour later in life.
The scientists from the University of Gothenburg in Sweden interviewed 70-year-olds in 1971-2, 1976-7, 1992-3 and 2000-2001.
They found that the number of 70-year-olds reporting sexual intercourse rose in men and women, married and unmarried.
More than two-thirds - 68% - of married men in the most recent survey said they had sex, an increase from 52%, while the percentage of married women having sex rose from 38% to 56%.
The number of men reporting physical problems, such as erectile dysfunction or ejaculation dysfunction increased.
The number of women who said they were highly satisfied with their sex lives rose too.
When sexual intercourse stopped, both men and women tended to blame men, in line with the findings from earlier surveys.
Professor Peggy Kleinplatz, from the University of Ottawa, said that doctors should now be trained to ask all patients - regardless of their age - about any sexual concerns.
She said: "Sex is an important and positive part of the lives of their 70-year-old participants, and more so for the current cohort of men and women than for their predecessors in 1971."
Dr Petra Boynton, a specialist in the psychology of sex and relationships at University College London, said it was important to remember that someone turning 70 in the year 2000 would have been influenced by the more free sexual attitudes of the 1960s and 1970s - and also perhaps fitter and healthier than those in their 70s in previous decades.
She said: "We still have this stereotype of elderly people with their bath chairs and canes, staggering around, who couldn't possibly be having sex - but that isn't the case."
She pointed out that the study did not record the frequency of sex for any of those surveyed, simply whether they were having sex at all, and focused on penetrative sex, rather than other types of sex which might be favoured by older people.
"I am slightly concerned that this will be interpreted in a way that suggests that if you're not having sex in your 70s, you are doing something wrong.
"There are still plenty of people who choose not to have sex."
Meanwhile, a report by Finnish researchers says older men who have more sex will experience fewer erection problems.
A five-year study, published in the American Journal of Medicine, of 989 men aged 55-75 in Pirkanmaa, Finland, showed that having sexual intercourse less than once per week doubled the risk of erectile dysfunction, compared to having sex once per week.