BZ: this article seems to fit in with the Gaia Portal published today in the line ~ “Patterns of ancients reappear, as corporate patterns dissolve.
Modern Life Suppresses An Ancient Body Rhythm
By Natalie Angier, published in the New York Times, on March 14, 1995
BETHESDA, Md.— AS the vernal equinox advances, and the sun lingers in the sky a bit longer each day, and the buds poke forth like babies’ fists from every barren twig, even urbanites may feel the pagan craving to revel in seasonal rhythms.
After all, the lengthening of the day and the warming of the air exert a tremendous influence on virtually every other life form, inspiring migrations, ending hibernations, inciting growth and exciting lust. Surely humans, too, must be prey to the power of the seasons, the return of light and the chastening of night. Surely people’s innate circadian clocks must react to the return of spring, resetting themselves to keep pace with the extra daytime hours.
As it turns out, human biological clocks do change but only in about half of all people — the half who are women. In men, however, the songs of the seasons apparently hit a deaf ear. The contemporary industrialized world, which blazes with artificial illumination, has suppressed men’s ability to react to changes in day length.
Women and men may sleep the same number of hours each night, they may spend the same amount of time bathed in a corporate fluorescent glow each day, but in women, at least one essential keeper of internal circadian rhythms ignores false idols of light and instead heeds only Helios, Ra, Mithras — the sun. When the sun rises late and sets with sorry haste, the amount of a key circadian hormone, melatonin, that is secreted in the female brain at night increases. Come summer, nocturnal melatonin release falls off.
The consequences of that seasonal hormonal shift remain unknown for humans, but in other species, annual changes in melatonin secretion serve as the principal signal orchestrating many of the behaviors that count, including a willingness to fly thousands of miles to one’s summering grounds and the desire to breed.
Among modern men, by contrast, though they retain all the machinery to react to seasonal change, the release of melatonin at the winter solstice is identical to that secreted during a midsummer night’s dream.
“Men seem to be more sensitive to artificial lights than women are,” said Dr. Thomas A. Wehr of the clinical psychobiology branch of the National Institutes of Mental Health here, who made the discovery of gender differences in circadian rhythms. Looked at another way, he said, grinning slyly, “When it comes to seasonal change, men just don’t get it.”
The surprising new finding is part of a larger study that Dr. Wehr and his colleagues are carrying out in the relatively unmined field of photoperiodicity in humans — the impact of day length on hormonal fluxes, sleep patterns and behavior. They are seeking to measure key indices of seasonal rhythms in humans and to see when, why and how those measures might change over the course of the year. Their work could explain why women suffer disproportionately from seasonal affective disorder, or SAD, a type of depression that strikes most often in winter.
In addition to the study of seasonal shifts, the researchers are attempting to tease apart the details of the body’s circadian clock, which operates on a 24-hour schedule and tells a person when to sleep, eat and be out and about. Through elaborate and demanding studies that require volunteers to be hooked up, prodded, bled and sampled like astronauts for weeks at a time, the scientists are attempting to determine what the human circadian clock may have behaved like in prehistoric times, before the advent of bright lights, big cities and all-night cybersex.
“It’s a kind of archeology, or human paleobiology,” said Dr. Wehr, 53. “We’re looking at what human hormonal, sleep and temperature patterns might have been like in a prehistorical period when there was very little artificial light around.”
Some of the scientists’ results are preliminary, and those describing gender differences in seasonal release of melatonin have yet to be published. Nevertheless, the work suggests that women and men live in slightly different nightly realms, and that women can add to the lunar timetable on which menstrual cycling is roughly based a gentle adherence as well to the calendar of the sun. However, Dr. Wehr points out that there may be male cadences as well, perhaps ones operating on a shorter timetable.
The new studies are part of a larger explosion of interest in biological clocks. Several weeks ago, scientists announced the discovery of a gene in plants that controls such circadian-based rhythms as the morning unfurling of leaves and the timing of photosynthesis. Writing in the current issue of American Scientist, Dr. Joseph S. Takahashi, a professor of neurobiology and physiology at Northwestern University, describes efforts to fish out the genes responsible for timekeeping in animals. One has been found in fruit flies, called the period gene, which assures that newly mature flies will emerge from their pupal cases in the morning, when the sun can quickly dry their wings. Another gene identified in the fungus Neurospora controls growth spurts. Dr. Takahashi and his co-workers are closing in on a gene called clock, found on both mouse and human chromosomes, that, when mutated, causes the body’s clock to think the world works on a 25-hour day.
When Dr. Wehr began studying photoperiodicity in humans, he was astonished to learn how little work had been done in the area. Animals, yes — their seasonal variations had been charted in detail. But studying the same thing in humans is hard, long-term work. Besides, many scientists assumed that people, being nonseasonal, year-round breeders and nonmigratory, were relatively immune to the effects of changing day length.
To explore the accuracy of such assumptions, Dr. Wehr and his colleagues attempted to recapitulate prehistoric sleep conditions in a posthistoric population, among 15 young men living in the Washington area. They began by exploring what happens when the men switched from the conventional day length, or photoperiod, of 16 hours, which the average working adult adheres to year-round with the help of lamps and coffee, to a shortened photoperiod of only 10 hours, a schedule that approximates what prehistoric people in the middle latitudes would have experienced in the dead of winter.
p itemprop=”articleBody”>Every night for four weeks the men came to the laboratory, where they spent 14 hours in windowless dark rooms, relaxing and sleeping as much as possible. Various hormone levels, temperature, brain waves and other functions were measured at regular intervals throughout the night. Later, similar measurements were made when the men came into the clinic to sleep for the more traditional seven to eight hours a night.
The researchers discovered a number of intriguing things about how ancestral humans may have spent their dark winter nights. For one thing, as the study volunteers adjusted to their artificial circumstances, their sleep patterns relaxed into distinct phases. The men slept only about an hour more than normal, but the slumber was spread over about a 12-hour period. They slept for about four to five hours early on, and another four to five hours or so toward morning, the two sleep bouts separated by several hours of quiet, distinctly nonanxious wakefulness in the middle of the night. The early evening sleep was primarily deep, slow-wave sleep and the morning episode consisted largely of REM, or rapid eye movement, sleep characterized by vivid dreams. The wakeful period, brain wave measurements indicated, resembled a state of meditation.
“This is a state not terribly familiar to modern sleepers,” Dr. Wehr said. “Perhaps what those who meditate today are seeking is a state that our ancestors would have considered their birthright, a nightly occurrence.” Dr. Wehr pointed out that many mammals, while they are secure in their dens, also sleep in bouts separated by stretches of quiet wakefulness.
During the enforced long nights, the levels of the hormone prolactin, which ordinarily double during sleep over daytime concentrations, switched into high gear shortly after the men entered their chambers, and remained elevated during the entire 14 hours. That perpetual prolactin surge could explain the overall peacefulness the men experienced. Prolactin is a compound that helps keep an animal resting; when birds brood their eggs, they stay still thanks to prolactin. The men’s melatonin release also kept pace with the contrived night. The pineal gland of the brain began secreting melatonin at the onset of darkness and it continued pumping the hormone out at fairly high levels until morning. The output of growth hormone, a chemical associated with bodily construction and repair, also remained high throughout the night.
When the men returned to the normal schedule of an eight-hour night, a host of fairly dramatic changes occurred. Melatonin secretion dropped off. The amount of prolactin released stayed the same, but it was compressed into a much shorter time frame. The peak of maximum growth hormone output during the night doubled over what it had been on the winter schedule. Body temperature stayed slightly warmer than it had been during the long nights.
These and other alterations in physiology persuaded the scientists that humans, contrary to previous notions, have retained their innate ability to respond strongly to changes in the length of day and night. How those seasonal adjustments might have affected the behavior of early man is unknown. Nor is it known whether people living in the tropics, where the length of day and night is constant throughout the year, would respond to changes in light conditions, or whether cues like weather and temperature changes might have the same effect on melatonin secretion and the like.
More recently, in a paper that will be published later this spring in the American Journal of Physiology, the Wehr team showed that these seasonal changes were suppressed by the impact of artificial lighting and the preferred Western pace. They took men who had been going about their daily lives on the standard pan-seasonal schedule of 16 waking, illuminated hours and put them in a dimly lit room for 24 hours, where they were kept awake and again sampled regularly for things like melatonin secretion. Because the body’s clock operates by a memory that lags for a day or two, the samples reflected the men’s hormonal indicators of day and night from the time preceding their foray into the laboratory. Measurements were taken for the same man once in winter and again in summer. And while the scientists’ previous studies showed that men can change their biological clocks from one season to the next when given the opportunity, these men, plucked from the real world for a day, showed no seasonal variation at all in melatonin secretion and other parameters.
The scientists found a gender difference in the seasonal response, not by looking for it, but as an incidental outcome of another study, an attempt to find the root cause of seasonal affective disorder. They wondered if sufferers of SAD might have seasonal variations in their melatonin secretions. Because most patients with the disorder are women, the researchers used healthy women as their control population. Subjecting SAD patients to the all-night sampling vigil they had put the men through earlier, the scientists found there was a significant difference in winter and summer pacemaking in the women with the affective disorder.
But to their astonishment, the investigators saw the same seasonal discrepancy in the healthy women as well. The winter patterns of melatonin secretion were long and more sustained; the summer pattern, shorter and with a lower maximum crest. All the women had been living according to the standard 16-hour up-and-ready schedule adhered to by their male counterparts. The women’s internal clocks, however — the part of the brain that responds to light and dark — was somehow keeping track of the seasons and adjusting melatonin output accordingly.
p itemprop=”articleBody”>Why women might be more resolutely photoperiodic than men remains a mystery. It could be a remnant of a time when humans, like many other mammals, tended to reproduce seasonally. In recent years, several scientists have found indications that humans still have semiseasonal breeding patterns, with peaks of fertility during spring and fall.
Beyond the gender difference, the work underscores how radically the change in human sleep patterns may be affecting biology and even behavior. By compressing all nocturnal biochemistry and all sleep patterns into an eight-hour period pretty much year-round, Dr. Wehr said, “we essentially live in an endless summer, from the day we are born until the day we die.” The consequences of that compression have yet to be charted.
Nor does Dr. Wehr suggest we should return to paleolithic ways of long, languid nights. “We like being awake and doing things, and we don’t want to go to bed early,” Dr. Wehr said. “We’re addicted to our endless summer.” After all, if one is not allowed to stay up late, what is the point of being an adult?
Graphs: “Natural Clocks: Similar Daily Cycles for 3 Organisms” shows levels of melatonin in three studies (algae, Japanese quall, human) (Sources: Poggeler, et al./Naturwissenschaften (algae); Kumar and Follett/Journal of Pineal Research (quall); Dr. Thomas A. Wehr, et al./American Journal of Physiology (humans) (pg. C3) Drawing (pg. C1)