But sexual problems are widespread. About 40 percent of the 4,507 respondents aged 40 to 80 reported having one or more difficulties, ranging from poor lubrication to erectile difficulties.
"We would think that sexual frequency wouldn't be very high as people age, but in fact it was surprisingly common," says Dr. Gerald Brock, lead author of the study and an associate professor of urology at the University of Western Ontario in Canada. "It tells us people in the second half of life are really very active."
The survey -- done in United States, Canada, Australia, and New Zealand -- was presented at the American Urological Association's annual meeting in Chicago earlier this week.
About 81 percent of men and 70 percent of women reported having sexual intercourse at least once in the past year, according to the survey.
Broken down by decade, about 90 percent of men aged 40 to 49 had sexual intercourse at least once during the past year; about 82 percent of men aged 50 to 59 did; about 80 percent of men aged 60 to 69 did; and about 52 percent of men aged 70 to 80 did.
As for women, about 89 percent of women aged 40 to 49 had sex at least once in the past year; about 78 percent of women aged 50 to 59 did; about 56 percent of women aged 60 to 69 did; and about 26 percent of women aged 70 to 80 did.
Some of the gap between the rates reported by men and women could be a bit of exaggeration on the part of men, Brock says.
But the main reason women gave for not having sex was not having a partner. Women were more likely to be widowed than men -- about 4.4 percent of men in the survey were widowers compared to 11.4 percent of the women.
The survey also found about 47 percent of men and 43 percent of women had sex five times or more in the past month. "These are people who are having regular, ongoing sexual intercourse with their partner," Brock says.
About 58 percent of men aged 40 to 49 had sex five or more times in the past month; about 50 percent of men aged 50 to 59 did; about 36 percent of men aged 60 to 69 did; and about 30 percent of men aged 70 to 80 did.
For women, those numbers were 57 percent for ages 40 to 49; 38 percent for ages 50 to 59; 20 percent for ages 60 to 69; and 8 percent for ages 70 to 80.
Still, sexual dysfunction is prevalent. For men, erectile difficulties were the most common lament, a problem that increased with age. About 13 percent of men aged 40 to 49 reported erectile difficulties as an ongoing problem (existing for three months or more). That went up to 36 percent in the 70 to 80 age bracket.
For women, poor lubrication was the most common problem. About 26 percent overall reported it, with the numbers peaking between the ages of 50 and 69.
Women were also twice as likely as men to report a lack of interest in sex -- about 34 percent of women compared to 18 percent of men. Women were also were more likely to say they didn't find sex pleasurable -- about 19 percent to 11 percent of men.
While about 40 percent reported at least one sexual dysfunction, only about 10 percent had discussed the problem with their physician.
"The vast majority of these problems can be effectively treated by physicians," Brock says. "Unfortunately, these issues are largely unmet because patients don't bring it up with their physicians and physicians don't ask about it."
Dr. Richard J. Macchia, professor and chairman of the department of urology at the State University of New York Downstate Medical School, questions defining "sexually active" as having intercourse once in the last year.
Some research has indicated men and women, as they age, may be more likely to engage in other forms of sexual activity, including masturbation, mutual masturbation, oral sex or manual stimulation.
As such, the survey, in dealing with intercourse only, doesn't really give a full and accurate portrait of the sex lives of people in these four countries, according to Macchia.
"Intercourse may be a highly limited definition," Macchia says. "It might not even be the most common activity."
A separate survey also presented April 29 revealed some additional details about sexual dysfunctions in women.
More than 1,140 women ages 21 to 80 who were members of an HMO in Detroit were given a 62-question survey that asked about their sexual behavior.
About 25 percent of women reported a lack of interest in sex, making it the most commonly reported dysfunction. Lack of interest was defined as a "persistent or recurring deficiency or absence of sexual fantasies, thoughts, and/or receptivity to sexual activity."
The second most common dysfunction, reported by nearly 20 percent of women, was "sexual arousal disorder," or a failure to become excited during sexual activity.
After each question about a particular aspect of sex, women were also asked if they were bothered by it and if they were interested in treatment.
"Something has to cause you personal distress for it to be a disorder," says Dr. Linda McIntire, lead author of the survey and an urologist at the Henry Ford Health System in Detroit. "If you are worried about it, if you want to change it, it's a dysfunction."
For example, a woman in her 40s might consider lack of interest in sex a problem, whereas woman in her 70s wouldn't, she says. Lack of interest in sex, therefore, wasn't considered a dysfunction in those women who weren't bothered by it.
The Columbia University College of Physicians and Surgeons has information on treatments for male sexual dysfunctions. The American Association of Marriage and Family Therapists has info for women.