The number of sexually active years one has left — "sexually active life expectancy" — may be influenced by health and gender, according to a study published in the BMJ, formerly the British Medical Journal.

By age 55, men have an average sexual life expectancy of 15 more years while women can expect 10 more years of activity, said study authors Dr. Stacy Tessler Lindau and Dr. Natalia Gavrilova of the University of Chicago. However, although men have an increased desire, poor health is more detrimental to their sexuality than it is for women.

"Widowhood at older ages is the main driving force of lower sexually active life expectancy among women because women live longer than men and most of them have older husbands," said Gavrilova, an expert on human longevity at U. of C.'s Center on Aging.

Older women, however, may welcome fewer years of sex. They're less interested in it than older men, even if they have a partner, according to the study. Among those age 55 and older, just 21 percent of women demonstrated interest in sex, compared to 62 percent among men.

The researchers found that healthy people were twice as likely to be interested in sex and have more of it than those in poorer health. Men were more likely than women to be sexually active, report a good quality sex life and be interested in sex, a gender gap that widens with age. The starkest difference was among 75- to 85-year-olds. In this group, about 39 percent of the men were sexually active, compared with 17 percent of women.