University of Chicago researchers have surveyed more than 3000 older Americans on their sex lives. The study paints one of the most complete pictures ever of the sexual activities of people between ages 57 and 85.

Americans are having sex in their 60s, their 70s, even into their 80s.

Researcher Linda Waite says the study provides an important benchmark to understand what normal sexuality is as people age.

"The population of the U.S. and many, many other countries in the world is aging," said Waite. "Aging adults are healthier than they've ever been. And this study tells us what older adults experience and how they feel about it."

According to co-author Stacy Lindau, most of the people in the study had a spouse or other partner, and most of those who did reported having sexual activity in the past 12 months. She says the pattern of sexual activity doesn't seem to change dramatically compared with previous studies of younger adults.

"An interesting finding is that among those who were sexually active, the frequency of sexual activity, was two to three times a month or more. So what that suggests is that if one has a partner, the frequency of sexual activity doesn't change a whole lot across age groups."

The researchers found that sexual activity does decline with age. Among women, for example, between ages 57 and 64, a solid majority ? 62 percent ? said they had had some kind of sexual activity with a partner in the past year; but among women over 75, that declined to 17 percent. Researchers note that much of that decline is related to poor health in old age or the death of a partner, not necessarily to a loss of interest.

Both men and women were more than twice as likely to have engaged in sexual activity in the past year if they considered themselves in excellent or very good health, compared with those who described their health as fair or poor.

Even though sexual problems can signal other health issues, the survey found that only about 30 percent of participants said they had discussed sex with a doctor since age 50.

Georgeanne Patmios of the U.S. National Institute on Aging, who was not part of the study team, welcomed the research, which she said would provide doctors some guidance as to what kind of sex lives their older patients might have.

"Despite the aging of the population, little has been known about sexuality among older adults, how sexual activities change with age and how sexual activities and problems are associated with health. These are the first comprehensive, nationally representative data on sexual activity, behaviors and problems in relation to health status among older Americans," said Patmios."

Co-author Stacy Lindau said it might also help doctors bring up issues of the sexual health of their patients, a matter which can sometimes be embarrassing on both sides of the stethoscope.

Another change noted in the study is the type of sexual activities engaged in. Co-author Linda Waite says that as people age they are more likely to engage in other types of sexual activity, rather than intercourse. "That declines slightly as people age, with more cuddling and kissing and snuggling as the primary activity."

The study on sex and older adults was published in the New England Journal of Medicine.