The average person's sex life ends by age 70, according to a report published Tuesday in the British Medical Journal.

At age 30, men have an average of 35 years of sexually active life remaining, compared with 31 years for women, researchers at the University of Chicago's department of obstetrics and gynecology estimated in the study. By 55, men have an average sexual life expectancy of 15 years and women can expect 10 more years, they found, based on data from two separate surveys.

People in very good or excellent health were almost twice as likely to be interested in sex as people in poorer health, according to the study. Men lost more years of sexual activity as a result of poor health than women, the researchers said. That may motivate men to pursue healthier lifestyles, they said.

The team, led by Stacy Tessler Lindau, used data from a 1995-96 survey of 3,000 men and women ages 25 to 74 and a 2005-06 survey of 3,000 men and women 57 to 85. Men were more likely than women to be sexually active, report having a good quality sex life and be interested in sex, according to the study.

The gap was largest among 75- to 85-year-olds. About 40 percent of men in that group were sexually active, compared with 17 percent of women, the researchers found.

The study was funded by the University of Chicago and the National Institutes of Health.