By Marilynn Marchione The Associated Press

An unprecedented study of sex and seniors finds that many older people are surprisingly frisky – willing to do, and talk about, intimate acts that would make their grandchildren blush.

That may be too much information for some folks.

But it comes from the most comprehensive sex survey ever done among 57- to 85-year-olds in the United States. Sex and interest in it do fall off when people are in their 70s, but more than a quarter of those up to age 85 reported having sex in the previous year.

And the drop-off has a lot to do with health or lack of a partner, especially for women, the survey found.

The federally funded study, done by respected scientists and published in yesterday’s New England Journal of Medicine, overturns some stereotypical notions that physical pleasure is just a young person’s game.

“Most people assume that people stop doing it after some vague age,” said sex researcher Edward Laumann of the University of Chicago.

However, more than half of those aged 57 to 75 said they gave or received oral sex, as did about a third of 75- to 85-year-olds.

“Bravo that the New England Journal of Medicine is publishing something like that. It’s about time,” said Ruth Westheimer, better known as sexpert Dr. Ruth, who has long counseled seniors on sex.

The survey involved two-hour face-to-face interviews with 3,005 men and women around the country. Researchers also took blood, saliva and other samples that will tell about hormone levels, sex-related infections and other health issues in future reports. They even tested how well seniors could see, taste, hear and smell – things that affect being able to have and enjoy sex.

Some results:

” Sex with a partner in the previous year was reported by 73 percent of people ages 57 to 64; 53 percent of those ages 64 to 75, and 26 percent of people 75 to 85. Of those who were active, most said they did it two to three times a month or more.

” Women at all ages were less likely to be sexually active than men. But they also lacked partners; far more were widowed.

” People whose health was excellent or very good were nearly twice as likely to be sexually active as those in poor or fair health.

” Half of people having sex reported at least one related problem. Most common in men was erection trouble (37 percent); in women, low desire (43 percent), vaginal dryness (39 percent) and inability to have an orgasm (34 percent).

” One out of seven men used Viagra or other substances to improve sex.

” Only 22 percent of women and 38 percent of men had discussed sex with a doctor since age 50.

The survey had a remarkable 75 percent response rate. Only 2 percent to 7 percent did not answer questions about sexual activities or problems, although a higher percentage declined to reveal how often they masturbate.

Why do this research? Sex is an important indicator of health, said Georgeanne Patmios of the National Institute on Aging, the study’s main funder.