Sex Sleep Eat Drink Dream (23 page)

There was also significant deactivation in the amygdala for women (less for men), leading the scientists to hypothesize that sex may distract us from events in the environment, even those that might justly invoke fear—perhaps, says Holstege, so that we can have sex "without being bothered by outside stimuli."

All of this activity may have some long-term health benefits. From the University of Bristol comes news that in men who reported the highest frequency of orgasm, the risk of fatal coronary events was halved—possibly because sexual activity offers a cardiovascular workout, or perhaps because men with a robust sex life are just happier and less stressed. Another study shows that college students who have sexual intercourse once or twice a week have 30 percent higher levels of immunoglobulin antibody than abstainers. And another, highly controversial study suggests that sex may have long-term positive effects on mood in women. In a sample of sexually active college females, researchers found that women who had intercourse without condoms had fewer symptoms of depression than those who used condoms or refrained from sex altogether. The scientists are quick to say that they do not recommend eliminating the use of condoms for psychological reasons, as sexually transmitted diseases or an undesired pregnancy would easily outweigh semen's benefits. But the study does suggest that some of the compounds present in semen that can be absorbed through the vagina, including testosterone, estrogen, and prostaglandins, may have an antidepressant effect.

A rush of pleasure; a reduction in stress, depression, and fear. Too bad we so often save sex for the end of the day and not the start.

11. NIGHT AIRS

I
T'S WELL AFTER
11
P.M.,
and you should be drifting off. Your partner is sleeping peacefully. But you're wide awake, nursing indigestion from dinner's too-large slab of beef, perhaps, or wheezing from asthma or the congestion of a wicked cold.

A sixteenth-century Italian priest, Sabba da Castiglione, cautioned his followers about the "numerous illnesses that night air is wont to generate in human bodies." You know that your blooming infirmity, whatever it may be, is not due to evil air. But it is true that many ills worsen at night. Fever spikes. Skin irritability flares. Gout, ulcers, and heartburn intensify.

Some of the ailments that stalk us in the hours of darkness are byproducts of the body's nocturnal protective mechanisms. At night many of our daytime defenses slow or shut down—our gag reflex, for instance, and the cilia that sweep clean the respiratory tract. The other mechanisms that fill the protective void, including stepped-up acid secretion and heightened inflammatory reactions, have the potential to wreak their own havoc, aggravating everything from ulcers to psoriasis. Low nocturnal levels of adrenaline and Cortisol (which ordinarily help keep breathing passages open during the day) make nighttime asthma attacks hundreds of times more common. Also, late night brings a shift in the workings of the lungs: Bronchia become more hy-perreactive, and the bronchial passageways that move air in and out of the lungs shrink in diameter by about 8 percent. For healthy people, this squeeze presents little problem. But for those with asthma, the constriction can reduce air flow to the lungs by 25 to 60 percent, causing the coughing, wheezing, and breathlessness of the disease.

Perhaps this feels more like a simple cold. Two tiny obstructive fists seem to have lodged in your nostrils. At the back of your throat is a sore, scratchy lump that makes it hard to swallow. Earlier today you were a whole, healthy person; now, it seems, you're the wretched host to a germ picked up somewhere, in an elevator or from a child who brought it home from school.

Nighttime is when activity for the body's immune cells is supposed to be peaking. Those glands swelling in your neck are filled with burgeoning populations of white cells known as lymphocytes. They're multiplying all right, but their full flowering against this insidious invader will take as long as a week. At the moment, they're not up to the struggle, and so you sniff and hack your way deep into night.

On average, adults get two to four colds a year; children, about four to eight. Researchers have carefully computed the disruption produced by these illnesses: In a typical year, the 500 million or so cold episodes in the United States cause some 400 million days of missed work and school, and more than 100 million doctor visits, for a total annual cost of up to $40 billion.

What is a cold, anyway? How did your spouse resist the germ that plagues you? Why does a bug register in one person as only a scratchy throat and put another in bed for a week?

The cold earned its name from the link stubbornly forged in folklore between catching a chill and contracting a cold. The Greek philosopher Celsus wrote in the second century
A.D.
that "winter provokes headache, coughs, and all the affections which attack the throat, and the sides of the chest and lungs."

Modern science deemed the cold-cold link a complete myth—until lately. The conviction that ambient temperature had little to do with susceptibility to infection grew out of a study in the 1950s. Scientists persuaded one group of more than two hundred volunteers to perch in a large freezer for two hours and another, equally large group to sit in their skivvies in a room at 60° F; then the whole crew of four hundred or so was exposed to a cold virus. All of the subjects contracted colds at about the same rate.

A decade later, a similar experiment was conducted after the discovery of the most common cause of the common cold, the rhinovirus (from the Greek
rhinos,
nose). Researchers placed the rhinovirus directly into the noses of inmates from a Texas prison, then exposed their subjects to extreme cold. Neither cold nor warmth, clothing or no clothing, wet hair or dry, affected their rate of infection, prompting the researchers to declare that no further studies were necessary.

Science, however, did not heed the advice, and a new study offers some evidence to support the old folk wisdom. In 2005, a team at the Common Cold Centre in Wales subjected ninety healthy volunteers to a body-chilling ice-water foot bath; ninety others in a control group stayed dry. In less than a week, almost a third of the chilled group had developed cold symptoms, compared with less than a tenth of the control group. The reason? When people are chilled, suggest the researchers, the blood vessels in their noses constrict, shutting off the blood supply to the white cells that fight infection. However, say skeptics, the "chilled" subjects were not tested for the presence of cold viruses; their cold symptoms may have been mainly subjective.

That colds tend to flourish in the chilly months is not because of temperature, but humidity and human behavior, argues Jack Gwaltney, a professor emeritus at the University of Virginia and an expert on the common cold. The rhinovirus's survival depends on moist conditions, above 55 percent humidity. More important, cold, wet days keep children densely packed inside nurseries, schools, and colleges, providing an ideal breeding ground for viruses. People, not weather, are the main problem, says Gwaltney: "The best way to avoid a cold is to live as a hermit; the best way to get one is to see a lot of children." Young noses are the major source of cold viruses. "If your child gets a cold, and you're not immune to that virus," he explains, "there's a 40 percent chance that you, too, will succumb."

Viruses are highly contagious bugs; small doses of only one to thirty particles are sufficient to produce infection. And just a day after being infected, a person can transmit the germ. While the average cold virus is most contagious within the first three days of illness, its particles are shed from nasal secretions for up to three weeks. These particles are surprisingly hardy and enduring. In a paper entitled "Rhinovirus transmission: one if by air, two if by hand," Gwaltney and his colleagues reported that rhinoviruses survive and remain infectious on surfaces—hands, doorknobs, counters—and are most commonly transmitted by finger-to-nose inoculation. During only ten seconds of hand exposure, the virus on a donor's hand is transferred to a recipient's fingers 70 percent of the time. Infection most often occurs when people touch a contaminated object or the fingers of infected individuals, then inoculate their own noses or eyes. The team found that transmission could be interrupted by cleaning the surfaces with disinfectant or even applying iodine to fingers.

Once inside your nose, cold viruses are absorbed by a thin film of mucus that coats the little shelf-like structures in your nasal passages called turbinates. Within ten or fifteen minutes, cilia lining the turbinates move the mucus and its baggage to the back of the throat, where they're swallowed and destroyed in the stomach. In unlucky cases, however, the virus particles carried in the mucus are deposited on your adenoids—lymph glands located above the roof of the mouth and behind the nose, which harbor cells to which the virus may readily attach. Here's the kernel of that thick, scratchy feeling in your throat. At first the adenoidal cells docilely accept the virus; later comes the storm. It takes about eight to twelve hours for a rhinovirus to rev up, complete its reproductive cycle, and produce new viruses. Soon thereafter, the cold symptoms begin.

Ah, the symptoms.

Despite popular belief, that stuffy, blocked feeling in your nostrils does not result from mucus but from the swelling of the turbinates caused by dilating blood vessels. These structures normally swell one at a time on an eight-hour cycle, even when you're cold-free. No one knows why, although some scientists speculate that the cycling may give one nasal chamber a rest while the other carries on the job of air conditioning. During a cold, however, both sides swell at once, and inhalation becomes a stifled affair.

The runny nose of a cold is born of thick mucus produced by "goblet" cells in the lining of the respiratory tract. This mucus is suspended in a watery fluid made from plasma that oozes out of junctions in the cells of the blood vessel walls lining the nose. The plasma carries antibodies and bradykinins—immune system chemicals that stimulate the pain nerve fibers in the nose and throat, causing soreness.

Beware the nose-blow, says Gwaltney: A new finding suggests that forceful nose-blowing may do more damage than good, propelling nasal secretions into the sinuses, where secondary bacterial infection can take hold.

If the tickle of mucus sufficiently irritates the nerve endings in your nasal passages, a message may flash up to the sneeze center in your brain. Thought to be located in the brain stem, the sneeze center coordinates the activity of muscles in the abdomen, chest, diaphragm, vocal cords, and throat, which contract, sending saliva flying out of your mouth and triggering copious nasal flow to wash away the offender.

Coughing can achieve even greater powers of expulsion. In most languages, the word for cough is imitative of a respiratory act so violent it can break blood vessels:
husten, toux, tosse.
First there's the sharp intake of breath, followed by a squeeze of muscles in the diaphragm and abdomen while the vocal cords close the glottis of the larynx for a fraction of a second. Then, as the glottis suddenly reopens, a rapid, powerful flow of air is released from the lungs at speeds of some five hundred miles per hour, blasting out whatever evil need be expelled.

Once considered a simple reflex, coughing is in fact a subtle mechanism. In the respiratory tract, from larynx to lungs, are sensory receptors that are triggered by irritants—mucus, smoke particles, and immune system chemicals. These receptors are the "master switches" of coughing. When stimulated, they fire a signal along the vagus nerve to the cough center, in the medulla area of the brain stem. (Here's where the active ingredients in some prescription cough remedies—opiates such as codeine—exert their calming effect.)

Runny nose, sneezing, cough. As Gwaltney points out, none of these cold symptoms result from any direct damage to the body by the cold virus itself, but from the exuberant action—or overreaction—of the body's own immune response. When Gwaltney and his colleagues biopsied cells of the nasal epithelium during a cold, they found no sign of destruction or injury by the virus. The rhinovirus and others like it produce illness by stimulating the body to do things that are harmful to its own cells and tissues. In fact, says Gwaltney, you can create a full-blown artificial cold in the body without the participation of any virus at all. Here's his recipe:

• A smidgeon of
histamines—
to get the nose dripping, dilate the blood vessels (causing that stuffy feeling), and stimulate the sneeze reflex. (It's not easy to provoke a sneeze, Gwaltney says. He tried tickling the nose of his subjects and giving them a snort of pepper; the only thing that worked reliably was placing histamine right on the nasal epithelium.)

• A pinch of
bradykinins
to stimulate the pain nerve fibers in the throat.

• A dash of
prostaglandins
to kindle a good cough and a headache.

• A sprinkle of
interleukin
to cultivate malaise.

Inject all ingredients into nose and wait.

These substances are all natural chemicals that mediate the body's inflammatory response—the first line of defense against injury or infection. Inflammation can occur nearly anywhere, in the skin around a splinter, in the joints (where it's called arthritis), in the brain (encephalitis), or in the lining of the nose (rhinitis). Unfortunately, in the case of a cold, all of this valiant inflammatory activity does not immediately rid the body of a virus. Sneezing and nasal irrigation may help remove dust or pollen from the nose, but not so virus particles; they're safely ensconced inside the actual cells of the nose, which we don't especially want removed. Once activated, inflammatory reactions tend to gain momentum, producing quantities of mucus for a week or so before the infection is resolved.