* Vaginal intercourse is reportedly the activity of choice for most people most of the time. But oral sex is popular too. In fact, among 75- to 85-year-olds, more than a quarter of men and a third of women say they either gave or received oral sex in the past year. (Rates among the under-75 crowd: More than half for both men and women.)
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* The studies did not report on alternative sexual practices, such as use of pornography, anal stimulation or sadomasochistic activities. But this might become a larger focus as geriatrics doctors treat successively more sexually liberal generations, Morley says.
He adds that, although we tend to stick with practices we know work for us, sometimes we're forced to adapt. As we age and lose our longtime partners, for instance, our new partners are more likely to be chosen based on intellectual and emotional factors than on sexual compatibility. So late-life couples could find themselves struggling to bridge gaps in sexual preferences.
* When researchers controlled for respondents' physical and mental health status, they found that aging itself didn't really cause sexual problems -- except for erectile strength. After the age of 40, the chances of having erectile problems increase by about 7% every decade. By the time they reach the 75-to-85 age group, more than 40% of men complain of serious erectile problems.
* For women, lack of interest in sex is a common problem (affecting about 45% of them), as is difficulty achieving orgasm (about 35%). But these tend to be lifelong issues; neither increases dramatically with age. Menopause often brings lubrication problems (with chances jumping from 20% to 40%), but increasing age doesn't bring an increased risk.
* Stressed, depressed or anxious women report less interest and pleasure in sex and more difficulties reaching orgasm. Men in the same mental states also report less interest in sex and more performance anxiety. (Or is it that men and women with sexual problems end up more stressed, depressed and anxious? The study can't say.) Depression in men is also tied to erectile problems, probably through side effects of antidepressants.
* There is a silver lining to aging: With increasing years, women are less likely to find sex painful, and men are less likely to complain of premature ejaculation.
* Although men are more likely than women to pin their overall happiness on having a good sex life, having poor health cuts a man's chances of being sexually active by a factor of 5, while similarly poor health cuts a woman's chances only by a factor of 3.
* For women more than for men, having a steady romantic partner strongly determines the quality of their sex life. Yet women are less likely to be married or in an intimate relationship at any age -- and it only gets worse with increasing years. Among 75- to 85-year-olds, for example, nearly 8 in 10 men have a steady partner -- but only 4 in 10 women do. (Women tend to outlive men of the same age, and men tend to pair up with younger women.)
Laumann notes that aging men are forced to become a bit more like women in their approach to sex. Because they can no longer rely on their own automatic sexual performance, they find themselves needing to ask more from their partners -- more cooperation, patience and skillful stimulation, for instance. Women, in turn, must adopt a more traditionally male approach to dating, Laumann says. With a shortage of available males in their age group, women who want a relationship are forced to more aggressively seek out partners and pursue men outside their usual circles.
* Contracting a sexually transmitted disease even once increases the chances of sexual problems later in life. For a woman, it nearly quadruples her chances of experiencing pain from sex and more than triples her chances of lubrication problems. Similarly, a man will be about 5 1/2 times more likely to find sex not pleasurable. It's unclear whether STDs themselves cause these problems, or whether some related factor in people's lifestyle is at work.
* Women who drink alcohol every day report more interest and pleasure in sex than their teetotaling counterparts. (Men showed no such link.)
Again, It's not clear whether a daily nip of brandy leads to better sex, or whether women who have fewer sexual problems also tend to imbibe more freely.
* Men who have had a sexual encounter with another man are five times as likely to lack interest in sex. Women with same-sex experiences show no such tendency.
* Less than 1% of men and women say they're in a same-sex relationship. Numbers are likely to grow as society becomes more comfortable with homosexuality, Morley says.
Overall, these results show a huge variability in preferences, Morley points out. "There's nothing wrong with sex as you get older, but there's also nothing wrong with not having sex. We don't become different people when we age. We're still just trying to do what makes us happy."
Nuzzo is a freelance writer.