Depressing as it sounds, researchers found women reach a peak of sexual activity with partners in their 30s, then begin a downward curve that extends for the rest of their lives.
But a prominent sex researcher said the results only tell part of the story of sexuality in the elder set. Just because older women don't have sex doesn't mean they're opposed to the idea, says Dr. John E. Morley, a professor of gerontology at Saint Louis University.
"There are a series of problems -- you can be ill, you can have no partner or your partner can be ill," he explains. The latter possibility is especially common because as many as four in 10 men are impotent by age 60, he adds.
The findings were based on a 1996 telephone poll and appear in the March 2003 issue of the journal Sexually Transmitted Diseases.
Researchers surveyed 2,000 women aged 18 to 94 in the continental United States in one of the only studies to examine sexuality in such a wide range of women.
About 80 percent of married women aged 18 to 29 reported having sex within the past three months, as did 55 percent of single women in that age group. Almost all of the sex reported was with men: just 2 percent of all women surveyed reported having lesbian sex.
The rate of recent sex dipped a bit among women in their 40s, then fell to about 55 percent among married fiftysomethings and 20 percent among single fiftysomethings.
Only about 35 percent of married women aged 60 to 94 reported having sex recently, as did just 5 percent -- or one in 20 -- of single women in that age group.
By the time they reached their 80s and 90s, only 2 percent of women reported recent sexual activity.
The survey was taken before the rise of the anti-impotency drug Viagra, so it's not clear if the rates of sex among older women have gone up.
The researchers devoted much of their focus to the use of condoms by women, especially the elderly.
Surprisingly, 12 percent of sexually active married women over the age of 60 reported using condoms during sex.
"These women may be using condoms to protect themselves from acquiring a sexually transmitted disease or for other reasons, such as prolonging their partner's erection," says study co-author Divya Patel, an epidemiologist at the University of Michigan School of Public Health.
Unmarried sexually active women older than 60 were only a tiny bit more likely to use condoms than their married counterparts -- 13 percent of them reported doing so.
Sexually transmitted diseases (STDs), of course, affect people of any age, and health officials have recently launched education campaigns to encourage safer sex among the elderly. "Regardless of age, women engaging in sexual activity with partners who might have STDs need to protect themselves," Patel says.
Morley, the sex researcher, isn't surprised by the findings about condoms.
"Safe sex is not something that older people grew up thinking about it," he says. "Most of them think if their partner is 60 or 70, sex has to be safe."
In fact, he says, prostitution arrests rise around the country when the government sends out social security checks, suggesting that elderly men are far from celibate.
"Men are men, and some of them do things that they probably shouldn't do," Morley says.
On the whole, he cautions, it's very difficult for researchers to figure out exactly how much sex people are having.
"If I phoned you and said, 'I'm here to do a sex survey' while your grandchild listened in, you're liable to say goodbye and put the phone down," he adds.
Even if they do agree to take a survey about sex, "most people probably are not likely to answer truthfully," he also adds. "Men always over-exaggerate the amount of sex they get, and women almost under-exaggerate."