"A majority of older Americans are sexually active and view intimacy as an important part of life, despite a high rate of 'bothersome' sexual problems," the National Institutes of Health (NIH) said in a report on the new study.
The research found that sexual appetite declines only slightly between the ages of 50 and 70, with many men and women practising vaginal intercourse, oral sex and masturbation well into their 70s and 80s.
Researchers at the University of Chicago surveyed 3,005 people aged 57 to 85, said the NIH, part of the US Department of Health.
The study "suggests a previously uncharacterized vitality and interest in sexuality that carries well into advanced age," said Richard Suzman of the National Institute on Aging (NIA) which took part in the study.
Half of those surveyed up to the age of 75 admitted to having oral sex, said the summary report released here Wednesday on the study, which is published in Thursday's issue of The New England Journal of Medicine.
More than half of men and a quarter of women admitted masturbating.
Nearly three-quarters of those aged 57 to 64 said they were sexually active. The figure dropped to just over half of those in the 65 to 74 age range, and a quarter of those aged 75 to 85.
Sexual activity was more common among older men than among older women.
The survey sheds light on the impact of physical health on people's sex lives, including sexual problems related to conditions such as arthritis, diabetes and hypertension, the report summary said. Overall health, it found, was more important than age in boosting a person's sex life.
The research may also help promote health education efforts to prevent sexually transmitted disease in older people.
"Sexual activity among older adults poses risks for new cases of HIV, as approximately 15 percent of newly diagnosed HIV infections are among Americans over age 50," the summary said.
About half of the sexually active older adults reported at least one "bothersome" sexual problem. More than a third of active men said they had erectile difficulties, and 43 percent of women reported "low desire."
American men spend more than a billion dollars each year on medications to improve their sexual function, the researchers said, with 14 percent of those surveyed taking medicine to boost their performance.