A significant number of older US citizens still have an active sex life, a new study has revealed.

University of Chicago researchers surveyed 3,005 people aged between 57 and 85 and found that many remain sexually active well into their 70s and 80s.

"There's no evidence to suggest that at some magical number of years, people sign off their hopes and desires and interest in relationships that involve love and intimacy," said Stacy Tessler Lindau of the University of Chicago, the study's leader.

The survey also showed that sexual activity was closely linked to overall health, which was far more important than age.

As health declined steadily after the early 70s, so did the prevalence of sexual activity, particularly for women.

Among those who remained sexually active, nearly half reported at least one sexual problem, such as lack of desire (43 per cent of women), vaginal dryness (39 per cent of women) or erectile dysfunction (37 per cent of men).

"There are a lot of people who feel that age is very tightly correlated with sexual activity or interest," Professor Edward Laumann of the University of Chicago, one of the report's authors, told the BBC.

"But it turns out that healthy people are sexually active if they have a partner, and that this is an important part of the quality of life."

Seventy-three per cent of those aged 57 to 64 said they had had sex with a partner in the last year, compared with 53 per cent of those aged 64 to 75 and 26 per cent of those aged 75 to 85.

People who said they were sexually active were having sex at least two or three times a month, the survey found.

And nearly half of the men and a quarter of the women said they masturbated regularly.