For many Senior Citizens, sexual activity doesn't abate but it clearly begins to fade away.

Desire and performance dim with the passing years and with poor health, researchers here reported, yet older adults, especially men, are often sexually active, Stacy Tessler Lindau, M.D., of the University of Chicago, and colleagues, reported in the August issue of the New England Journal of Medicine.

A nationwide survey of 3,005 U.S. adults, ages 57 to 85, found that sexual activity may continue into the ninth decade of life, although the prevalence was uniformly lower among women and, not surprisingly, among those in poor health.

In addition, the researchers said that although sexual problems are frequent among older adults, these problems are rarely discussed with a physician. Clinicians should be aware that sexual problems may be a warning sign or a consequence of a serious underlying illness such as diabetes, infection, urogenital tract conditions, or cancer, the researchers added.

The findings came from a national probability sample of 1,550 community dwelling women and 1,455 men. Interviews were in English and Spanish from July 2005 through March 2006.

The majority of this group are engaged in spousal or other intimate relationships and regard sexuality as an important part of life, the researchers said.

To be sure, the prevalence of those sexually active declined from 73% among respondents ages 57 to 64, to 53% among those ages 65 to 74, and to 26% among those ages 75 to 85.

However, even in the oldest group, 54% of sexually active persons reported having sex at least two to three times a month, and 23% reported having sex once a week or more.

Women were significantly less likely than men at all ages to report sexual activity, the researchers reported. In the subgroup of respondents age 75 to 85, 38.5% of men and 16.7% of women reported sexual activity with a partner in the previous 12 months.

The impact of age on the availability of a spouse or other intimate partner was particularly marked among women, the researchers noted. A total of 78% of men, age 75 to 85, compared with only 40% of women reported having such a relationship.

The age structure of the marital relationship and the earlier death rate of men compared with women may help explain the difference, the researchers said.

Among sexually active respondents, about half of both men and women reported at least one bothersome sexual problem.

The most prevalent sexual problems among women were low desire (43%), difficulty with vaginal lubrication (39%), and inability to climax (34%).

Among men, the most prevalent sexual problems were erectile difficulties (37%).

Fourteen percent of all men reported using medication or supplements in the previous 12 months to improve sexual function whereas only 1% of women did so. Nevertheless, only 38% of men and 22% of women reported having discussed sex with a physician since the age of 50.

Men and women who rated their health as poor were less likely to be sexually active, with poor health being even more important than age.

Compared with respondents who rated their health as good or excellent, those in fair or poor health had more sexual problems including difficulty with erection or lubrication, pain, or lack of pleasure. Also, women with diabetes were less likely to be sexually active.

The adjusted odds ratio for being sexually active among those who rated their health as "poor" or "fair" compared with those rating their health as "good" or "excellent," was 0.21 (95% CI 0.14-0.32) for men and 0.36 (CI 0.25-0.51) for women.

In discussing the study's limitations, the researchers said that because only specific sexual problems were assessed, the extent of sexual problems in older people may have been underestimated. Furthermore, this bias may increase with age as persons with sexual problems are likely to discontinue sexual activity.

As with most sexuality research, the data were self-reported, although the interview methods are well accepted as being valid, they noted.

In an accompanying editorial John H.J. Bancroft, M.D., of the Kinsey Institute at Indiana University in Bloomington, wrote that "until recently older adults tended to keep quiet about their sexuality because younger people assumed that they were not and should not be sexually active. Now the pendulum has swung, and the emphasis is increasingly on the provision of medical treatment to foster it."

Perhaps a middle ground is preferable, Dr. Bancroft said. For some older people sex is important in their relationship and well-being, and may benefit from counseling and medication.

Other couples, he said, choose to leave sex behind as they settle into later life. Often negotiation between partners is needed. "The medical profession," he wrote, "should encourage older patients to feel comfortable in discussing sexual problems and in choosing whichever of these two options suits them best."