Why Women Have Sex (42 page)

In the Meston Sexual Psychophysiology Lab, we decided to look at exercise, which also increases SNS activity. The women visited the lab on two separate days. On one of the days, they simply watched a travel documentary followed by an erotic film. On the other day, they exercised for twenty minutes on a stationary cycle or a treadmill just before watching a similar film sequence. They exercised at 70 percent of their maximum heart rate, which is a pretty intense workout for most people. On both days, a vaginal photoplethysmograph measured the women’s sexual arousal while they watched the films. As it turned out, on the days the women exercised before viewing the films, they showed a much greater increase in vaginal engorgement from the sexual films. In fact, their sexual arousal to the film was a whopping 150 percent greater on the days they exercised. So, in addition to preparing our bodies for the “fight or flight” response, activation of the SNS prepares a woman’s body for sexual arousal.

This finding is quite different from what research has found in men. Activation of the SNS impairs a man’s ability to get an erection, especially if he is concerned about his sexual abilities. The finding from the Meston Lab suggests just the opposite for women—that activation of the SNS might help women who have sexual problems. If a women is “into” having sex psychologically, but her body is not responding, she might try doing something energizing—chase her partner around the block (or better yet, have the partner chase her), go dancing, or watch a scary movie together. Many self-help books tell women who have problems becoming sexually aroused or having an orgasm to do the opposite—relax the body by listening to soothing music, take a bubble bath, or do some quiet meditation. Certainly these calming techniques are helpful
for clearing and relaxing the mind, but research from the Meston Lab suggests they would not “jump-start” the woman’s body for sex as effectively as an invigorating activity would.

A few years ago, the Meston Lab research team went to several theme parks in Texas to examine whether riding a roller coaster, which increases SNS activity, might be another way to enhance sexual responses. Having women insert vaginal probes at a family-oriented amusement park was obviously not an option, so the team was unable to measure women’s genital sexual arousal directly. Instead, they measured sexual attraction. So for several days, the research team interviewed heterosexual women who were waiting in line to ride a roller coaster and women who had just gotten off the ride. The post-ride women were still in a state of heightened SNS arousal. The researchers asked the women to look at a photograph of a man and then fill out a brief questionnaire that asked how attractive they thought the man was, how much they would like to kiss him, and how willing they would be to go on a date with him. Even though all the women viewed the same photograph of an average-looking man, the women who had just gotten off the roller coaster rated the man as being more attractive and having higher dating potential than did the women who were waiting in line to take the ride. It appears that attraction increased as a result of residual SNS activation from the roller coaster ride.

Pragmatic daters and maters may wonder whether the findings from the roller coaster study mean they would have a better chance of attracting a mate if they frequented locales that offered dancing instead of lounging, or if they hung out at a gym instead of a coffee shop. The answer is not straightforward. In real-life dating situations, it depends on whether there is at least some initial level of attraction. If so, then yes, perhaps. But if the woman does not find her pursuer in the least bit appealing, then even having her run a marathon would not make her want to go on a date, much less have sex with the person.

This notion that SNS activation can increase sexual arousal and attraction for women is a new concept for most people today. Some clever
men, however, figured this out long ago. As far back as AD 550, recordings of the Roman circus noted:

Women stood up in the stands drumming with their fists on the backs of people in the seats before them and screaming hysterically: “Kill!, Kill!, Kill!” Even before the games started, smart young men could spot women who would give way to this madness and make a point of sitting next to them. While in the grip of hysteria, the women were unconscious of everything else and the boys could play with them while they screamed and writhed at the bloody spectacle below them.

Worldwide studies confirm that women experience depression twice as often as men. Over a lifetime, approximately 20 percent of women and 10 percent of men become depressed. Differences in the release of sex hormones partially explains why more women than men are depressed. Evidence for this includes the fact that girls are more susceptible to depression than boys—but only after they begin menstruating and experiencing the associated hormonal changes of puberty. In men, testosterone levels fluctuate slightly throughout the day, with levels being the highest in the morning. But in women, levels of sex hormones such as estrogen and progesterone vary tremendously across the menstrual cycle. A woman’s menstrual cycle is usually twenty-eight days, and if you count the first day of a woman’s menstrual period as day one, then estrogen peaks around day twelve (just before ovulation) and progesterone is highest around days nineteen through twenty-two.

Women’s sex hormones also change dramatically with life events such as puberty, pregnancy, delivery and post-pregnancy, and perimenopause. Such radical shifts in sex hormones negatively impact a number of brain chemicals and physiological processes that cause depression. This can also explain why as many as 5 percent of women experience symptoms of depression and anxiety the week before their menstrual period, a condition known as premenstrual dysphoric disorder. And it helps to explain why such a high proportion of women become depressed at times when they are experiencing dramatic changes in their sex hormones.

Sex differences in the production of the hormone melatonin can explain why women are three times more likely than men to experience seasonal affective disorder, or SAD—a form of depression that results from seasonal changes in the availability of natural light. Our bodies respond to decreases in daylight by secreting melatonin from the pineal gland, a small structure that resides deep in the brains of mammals. Melatonin creates a sense of sleepiness (which is why many people with insomnia take melatonin supplements). As morning approaches and light hits the retinas of the eyes, melatonin levels decrease, which in turn increases alertness or wakefulness. Given that nights are longer in winter than in summer, humans and other mammals secrete more melatonin in the winter. And because winter is when most people with SAD become depressed, scientists believe that SAD may be caused by too much melatonin.

If all mammals increase melatonin production in the winter, why is SAD so much more common in women than in men? Researcher Thomas Wehr and his colleagues at the National Institute of Mental Health have shown that it may be because women are more physiologically responsive to changes in exposure to light than are men. In our everyday life, we are exposed to lots of artificial light during the evenings, and one would think that this would affect melatonin production by “tricking” the brain to act as if it is daytime. When the researchers tested this hypothesis, they found an interesting gender difference: Regardless of the amount of artificial light they were exposed to, women much more than men were somehow still detecting and being influenced by the natural light. So, for women, the amount of melatonin secreted was greater in winter than in summer. For men, the artificial light seemed to compensate and they did not show the same degree of seasonal differences in melatonin secretion.

Prolonged stress that disrupts the body’s delicate hormonal equilibrium can also cause depression in both men and women. The brain uses neurotransmitters to chemically communicate information that controls our thoughts and behaviors. There are many different types of neurotransmitters in the brain, but three in particular have been linked closely with mood: serotonin, norepinephrine, and dopamine. If the production of these neurotransmitters is somehow compromised, it
can cause a region in the brain’s limbic system to malfunction. The limbic system controls our emotions, appetite, sleep, certain thought processes, and sex drive—all of which are impaired when a person is depressed.

Stress also causes the adrenal glands, which sit on top of the kidneys, to secrete more cortisol. Cortisol is a hormone that increases the body’s metabolism. Under normal levels of stress, Cortisol levels increase and then gradually return to normal. Prolonged stress, however, can cause extended Cortisol secretion, and this may be another cause of depression. We now know that Cortisol levels are abnormally high in about half of all severely depressed people. As it turns out, estrogen, which is produced in much higher quantities in women than in men, can not only increase Cortisol secretion, but it can impair the body’s ability to shut down Cortisol production post-stress. This could provide yet another explanation why more women than men suffer from depression and anxiety disorders. Also, given that sexual arousal and orgasm have been associated with decreases in Cortisol, elevated Cortisol could impair women’s sexual response. In a recent study conducted in the Meston Lab, women who had higher levels of Cortisol in response to viewing an erotic film were more likely to experience sexual desire and arousal problems than were women who showed the expected decrease in Cortisol while viewing the film. On the flip side, having sex could help, at least temporarily, alleviate anxiety and depression by decreasing Cortisol levels.

Many studies have shown that when women are depressed, they frequently experience sexual problems such as decreases in sexual desire and arousal. As we discussed in chapter 2, a number of drugs used to treat depression can impair sexual functioning. So, for women who are being treated with drugs for depression, it is sometimes hard to know whether the sexual problems are caused by depression or by the medication used to treat the depression. In another study conducted in the Meston Lab, close to one hundred college women who were in sexual relationships filled out a questionnaire that measured depression as well as sexual functioning. An anonymous and confidential code number assured the women that no one would know which response was theirs, making them more likely to answer the questions openly and honestly.
None of the women in the study were taking antidepressant medications. When the sexual functioning answers from moderately depressed women were compared to those of the nondepressed women, the researchers found that the depressed women experienced less vaginal lubrication and more pain during sex, had a harder time reaching orgasm, and felt less overall sexual satisfaction and pleasure than the nondepressed women did. The study also revealed a new and surprising finding: The depressed women masturbated much more often than the nondepressed women.

Why did depressed women find masturbation more rewarding than sex with a partner? One explanation is that the depressed women were masturbating as a “self-help” treatment—trying to feel better by having an orgasm. The endorphins released during orgasm create a temporary, but intense, sense of well-being. Because depressed women may find very little pleasure in their lives, even the short-term feel-good experience brought on by orgasm provides a meaningful mood-enhancing escape. Most women, even if they are not depressed, find it easier to have an orgasm through masturbation than with a partner—they know just the right places to touch and the amount of pressure that feels best. Also, having sex with another person requires a certain degree of social interaction—something that depressed people tend to avoid. And having sex solo would be unlikely to create “performance anxiety” or fear of being evaluated in the way that having sex with another person sometimes does.

At times masturbation may provide benefits over partnered sex, but research conducted by psychologist Gordon Gallup of the State University of New York in Albany suggests there might also be benefits to having sex with a partner—a male partner, that is. In the study, 293 college women filled out a depression inventory and also a questionnaire about their sex lives that asked things such as how often they had intercourse, how long it had been since their last sexual activity, and what type of birth control they used. As it turned out, the women in the study who had sex
without
using condoms (but may have used oral contraceptives) were significantly less depressed than the women who
had intercourse and used condoms as a regular form of birth control. They were also happier than the women who reported not having any sex at all. Perhaps the most shocking results came from the question on whether the women had ever attempted suicide. Over 13 percent of the women who said they always used condoms had attempted suicide in the past, compared with only 5 percent of women who said they never used condoms.

These findings suggest that there is something in semen that helped “cure the blues,” something that women who used condoms or abstained from intercourse were not getting. It has been known for a long time that semen contains nutritional substances that help sperm make the journey through a woman’s fallopian tube to capture that coveted egg. What fewer people know is that semen contains hormones including testosterone, estrogen, follicle-stimulating hormone, luteinizing hormone, prolactin, and several types of prostaglandins. All of these hormones have potential mood-altering abilities and can be absorbed into a woman’s bloodstream through the vaginal walls. In fact, some of the hormones have been detected in women’s blood within only hours of exposure to semen. Of the various semen-carrying candidates, estrogen and prostaglandins seem most likely to be the mood elevators. Both of these hormones have been shown to be lower than normal in depressed people, and estrogen has been shown to have mood-enhancing effects among postmenopausal women. Among younger women, there have been a few reports showing that certain estrogen-based contraceptives have mood-elevating properties.