Quotes of the Day
The "sex glow." Carrie Bradshaw and her Sex and the City trio may be the champions of detecting it, getting it and keeping it, but you don't need a closetful of Prada to appreciate the rosy radiance that follows a pleasant sexual encounter. The fact is, sex leaves its mark, not just on the mind but on the body as well. Researchers have begun to explore its effects on almost every part of the body, from the brain to the heart to the immune system.
Studies are showing that arousal and an active sex life may lead to a longer life, better heart health, an improved ability to ward off pain, a more robust immune system and even protection against certain cancers, not to mention lower rates of depression.
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But finding mechanisms for these benefits and proving cause and effect are no easy matter. "The associations are out there, so there has to be an explanation for it," says Dr. Ronald Glaser, director of the Institute of Behavioral Medicine Research at Ohio State University. Thanks to a better understanding of the biochemistry of arousal, as well as advances in imaging techniques, doctors are closing in on some possibilities. Their efforts are leading them to the hormone oxytocin, which may be the key lubricant for the machinery of sex. Known for controlling the muscles of the uterus during childbirth, oxytocin surges up to five times as high as its normal blood level during orgasm. Studies in animals have also revealed oxytocin's softer side. It is responsible for helping individuals forge strong emotional bonds, earning its moniker as the cuddle hormone. Released in the brain, oxytocin works in the blood, where it travels to tissues as distant as the uterus, as well as along nerve fibers, where it regulates body temperature, blood pressure, wound healing and even relief from pain.
While it is unlikely that oxytocin alone is responsible for sex's wide-ranging effects on the body, researchers hope that by tracking the hormone they can expose the network of body systems affected by sexual activity and identify other biochemical players along the way. Here's what they have learned so far:
--THE HEART OF THE MATTER
The strongest case that can be made for the benefits of sex come from studies of aerobic fitness. The act of intercourse burns about 200 calories, the equivalent of running vigorously for 30 minutes. During orgasm, both heart rate and blood pressure typically double, all under the influence of oxytocin. It would be logical to conclude that sex, like other aerobic workouts, can protect against heart disease, but studies in support of this link have yet to be done. "Can we make the claim that having sex is equal to walking a mile or bicycling? We don't know," says Robert Friar, a biologist at Michigan's Ferris State University. "The data don't really exist."
At least not yet. A study conducted in Wales in the 1980s showed that men who had sex twice a week or more often experienced half as many heart attacks after 10 years as men who had intercourse less than once a month. The trial, however, did not include a parallel group of randomly chosen control subjects, the scientific gold standard. So it's unclear whether frequent intercourse was responsible for the lower rate of heart attacks or whether, for example, the men who were sexually active were healthier or less prone to heart disease to begin with.
More recent research has focused on the hormones dehydroepiandrostone (DHEA) and testosterone, both important for libido. They have been linked to reducing the risk of heart disease as well as protecting the heart muscle after an attack. That may explain why doctors maintain that sex after a heart attack is relatively safe.
--PAIN CONTROL
In the 1970s Dr. Beverly Whipple of Rutgers University identified the female G spot, the vaginal on-switch for female arousal, and stumbled upon one of oxytocin's more potent effects: its ability to dull pain. Whipple showed that gentle pressure on the G spot raised pain thresholds by 40% and that during orgasm women could tolerate up to 110% more pain. But she could not explain the link until the advent of functional magnetic resonance imaging (fMRI). Using fMRI to view the brains of easily orgasmic women as they climaxed, either with visual stimuli or by self-stimulation, Whipple found that the body's pain-killing center in the midbrain is activated during peak arousal. Signals from this part of the brain instruct the body to release endorphins and corticosteroids, which can temporarily numb the raw nerve endings responsible for everything from menstrual cramps to arthritis and migraine for several minutes. Activating this region also reduces anxiety and has a calming effect.
--HE HEALING POWER OF SEX
A trial involving more than 100 college students in 1999 found that the levels of immunoglobulin, a microbe-fighting antibody, in students who engaged in intercourse once or twice a week were 30% higher than in those who were abstinent. Curiously, those who had sex more than twice a week had the same levels as those who were celibate. Could there be an optimal rate of sexual frequency for keeping the body's defenses strong?
Researchers in Sweden are meanwhile exploring how sex affects another immunological function: the healing of wounds. Here again, oxytocin may lead the way. Using injections of oxytocin as a surrogate for arousal, Swedish investigators have found that sores on the backs of lab rats heal twice as fast under the influence of the hormone as without it.
To find out whether the hormone has the same healing effect in people, Ohio State's Glaser and his wife Janice Kiecolt-Glaser, a psychologist at the same institution, are enrolling married couples in an unorthodox study in which each spouse's arm is blistered and then covered with a serum-collecting device. Over a 24-hour observation period, the couples discuss positive aspects of their marriage and mates as well as points of contention, such as finances or in-laws. The Glasers will analyze how levels of oxytocin change during these discussions, along with rates of healing.
--A LONG, HAPPY LIFE?
It's well known that married folk tend to live longer and suffer less depression than singles do. But is this because of more frequent sex, simple companionship or some benign aspect of personality that lends itself to marriage? Teasing apart such matters is difficult, but sex itself appears to be factor. A study of 3,500 Scottish men, for example, found a link between frequent intercourse and greater longevity. A much smaller study of elderly men found that those who masturbated appeared to experience less depression than those who did not. In addition, frequent sexual activity has been tied to lower risk of breast cancer in women and prostate cancer in men, a relationship that is still not fully understood but may involve some interaction between oxytocin and the sex hormones estrogen and testosterone and their roles in cell signaling and cell division. "Scientifically, it's an exciting time that will lead to a lot of rethinking and reconceptualizing of human sexuality," says Dr. John Bancroft, director of the Kinsey Institute. As the answers come in, the human race may begin to appreciate that the "sex glow" stays with them a lot longer than they realized.
- Alice Park