From Fertility to Mood, Sunlight Found to Affect Human Biology

The New York Times published an article on June 23, 1981 sharing scientific research that shows how sunlight affects the human biology.  Topics include fertility, mood, hormones, sleep, depression, mental health, and the effects of artificial lighting.

From Fertility to Mood, Sunlight Found to Affect Human Biology

By Jane E. Brody
Published: June 23, 1981

As the sun shone from its northernmost point Sunday, bringing the summer solstice – and the longest day of the year – to the Northern Hemisphere, a mysterious hormone that may influence fertility, mood and many other body functions should have reached its annual low point in the blood of those who spent the day outdoors, according to a new finding that may ultimately revolutionize studies of the effects of light on people.

Thanks to the interplay between sunlight and this hormone, the research suggests, Sunday may have been the happiest day of the year for peoples living north of the equator.

The hormone, melatonin, is released from a tiny gland in the brain, called the pineal gland, at night. In some birds and reptiles, this gland is exposed on the top of the head and acts as a ”third eye,” sending messages about light levels to the brain. The new studies, by Dr. Alfred Lewy, a research psychiatrist, show that exposure to very bright light, such as daylight, can turn off production of melatonin in people.

The finding contradicts the generally held assumption that, through evolution, human beings escaped altogether from the profound hormonal effects of light seen in lower animals, where the visible part of the spectrum regulates the reproductive cycle and many other daily and seasonal rhythms. Body rhythms in people were believed to respond primarily to psychosocial rather than biochemical cues. In fact, however, the new study suggests that people may have adapted to low-level artificial light while remaining sensitive to the much more intense natural cycle of light and dark.

This discovery accounts for several observations of seasonal rhythms in human beings that are similar to those seen in lower animals. These rhythms are more pronounced in people who live far from the equator, suggesting that people are responding to the natural sunlight-dark cycle and are not influenced by artificial lighting.

In Finland, for example, the conception rate peaks in June and July, when Finns are exposed to about 20 hours of sunlight a day. And in the temperate and polar zones, there are seasonal patterns in depression, mania and suicide attempts.

Dr. Lewy pointed out that in New York City the longest day is twice as long as the shortest (the winter solstice) and that people could be expected to secrete more melatonin during the longer nights of winter.

His and other recent studies raise serious questions about the adequacy of most indoor lighting and especially about energy-saving lights that greatly distort the natural spectrum of the sun. The studies show that to affect hormone production, human beings require much brighter light than other animals – three to four times brighter than the lights normally in homes, offices and factories.

”In the last hundred years, we’ve cut ourselves off from the light we evolved with,” said Norman T. Gilroy of the Center for Responsive Design, a nonprofit organization in San Francisco. Typical indoor lighting has less than 10 percent of the intensity of outdoor light under the shade of a tree.

Until very recently, only visual acuity was considered in designing indoor lighting. ”People don’t need much light to see,” Dr. Lewy noted. ”But far more intense light is needed to affect melatonin secretion and other circadian rhythms in human beings.”

Dr. Richard J. Wurtman, professor of endocrinology and metabolism at the Massachusetts Institute of Technology, worked out the daily cycle of melatonin secretion and has been studying the biological effects of light for nearly two decades.

He believes that ”we are all unwitting subjects of a long-term experiment on the effects of artificial lighting on health. Until much more is known, we should design indoor lighting to resemble as closely as possible what the sun provides.”

Meanwhile, Dr. Wurtman suggested that people spend as much time as possible outdoors and open curtains and windows to let in unfiltered daylight. Mr. Gilroy recommended using full-spectrum bulbs and special windows that let in ultraviolet rays.

Incandescent bulbs used in homes provide light primarily from the red part of the spectrum. The cool-white fluorescent lamps of offices, factories and institutions emphasize the yellow-green portion. Neither is a notable source of the invisible ultraviolet or infrared radiation found in natural daylight, which has a more even distribution of the spectral colors. The only commercially available light source that approximates the sun’s spectrum is ”Vita-Lite,” a fluorescent bulb that costs three to five times more than cool-white fluorescents, though not more to operate.

Dr. Wurtman and other scientists investigating responses to light believe that people who spend most of their days indoors illuminated by lights that are a poor substitute for the brightness and spectrum of the sun could suffer untoward effects from inadequate light exposure. In experimental animals, prolonged exposure to ordinary indoor lighting has been linked to reproductive abnormalities and enhanced susceptibility to cancer. Various Effects on People

Preliminary studies in people have suggested such problems as increased fatigue, decreased performance, diminished immunological defenses, reduced physical fitness and possibly impaired fertility associated with living and working under incandescent or cool-white fluorescent lights.

Dr. Philip C. Hughes, director of environmental photobiology at the Duro-Test Corporation in North Bergen, N.J., reports that the Russians now prescribe daily doses of ultraviolet light for workers deprived of sunlight exposure. Mr. Gilroy said that several American unions are demanding more healthful lighting in offices.

Bone loss due to inadequate vitamin D formation in the skin also occurs in people expgsed only to ordinary indoor light. Vitamin D, most of which results from exposure to the sun’s ultraviolet rays, is needed to absorb calcium from the diet, and many people in northern latitudes become deficient in vitamin D during the winter. The problem is most serious among those who spend the daylight hours indoors, and foods fortified with vitamin D are not always adequate compensation.

Attempts to use the energy-efficient but spectrally limited sodium vapor lamps indoors have met with a slew of immediate health complaints, including eyestrain, headache and nausea, and such lamps have been removed from several schools. This has prompted Dr. Wurtman to urge that ”novel lighting first be tested for health effects before exposing people.”

Different parts of the spectrum have different effects. While the invisible ultraviolet is needed for vitamin D synthesis and suntanning, the visible part of the spectrum influences body rhythms and hormone levels.

Light exerts its internal biochemical effects through the eye. Light passes through the retina to the optic nerve. Part of the optic nerve goes to the brain’s vision center and the other part goes to a section of the hypothalamus, the superchiasmatic nucleus, which is the body’s internal clock. From this nucleus, the light-generated nerve message travels through the brain to the spinal cord and out a nerve center, called the superior cervical ganglion, that transmits it to the pineal gland.

Dr. Lewy, a psychiatrist who is now director of the Sleep and Mood Disorders Laboratory at the University of Oregon Health Sciences Center, has shown in a preliminary study that some persons who suffer from periodic mental depressions are unusually sensitive to light, though not nearly as sensitive as other animals. In these patients, a lower level of light is required to suppress melatonin secretion. Even those who have recovered seem to retain their supersensitivity to light.

While at the National Institute of Mental Health, Dr. Lewy and his colleagues successfully treated a victim of manic depression who suffered from winter-long depressions that disappeared each spring. By exposing him for six hours a day – three hours at dawn and three at dusk – to high-intensity light that mimics the spectrum of the sun, the man’s depression lifted in four days and he has remained well.

”In a sense we made spring come earlier for him,” the psychiatrist noted. ”We expect to have to repeat the treatment next fall.”

As a result of Dr. Lewy’s research, the once dimly lit patient rooms at the mental health institute are now brightly illuminated with high-intensity, full-spectrum bulbs. In his new lab in Portland, Ore., Dr. Lewy plans to test light treatment in patients who become depressed in winter and recover in spring, as well as patients with other kinds of seasonal illnesses, such as ulcers. Many who suffer from cyclical depressions have disturbed circadian rhythms, possibly indicating abnormal pineal function, he said.

Rather than melatonin excess or lack acting as a direct cause of mental ills, Dr. Lewy believes the hormoneserves as ”a marker for what’s going on in the brain, the result of many biochemical processes.” Recently Dr. Lewy has been studying blind persons and has found that they have different melatonin rhythms than those who can see.

Though in nocturnal animals the pineal gland responds to light as dim as that provided by a quarter moon or a candle, in humans, ordinary room lighting does not shut down melatonin formed experiments with people, interrupting their nights by turning on the lights, saw no effect on melatonin levels and assumed that, as intelligent beings, humans were immune to control by so basic an environmental factor as light. A Different Tactic

Dr. Lewy tried a different tactic. After spending three years working with Dr. Sanford P. Markey to perfect a technique for precisely measuring melatonin in blood and urine, he studied volunteers who slept not at night but during the day for a week, until their usual melatonin cycle – high production at night, none during the day -was reversed. This is similar to the effect of traveling from the East Coast to the West Coast. Then he awoke the subjects in the middle of their sleep and exposed them to sunlight. A precipitous drop in melatonin levels occurred. Later, he repeated the studies during the night, using high intensity artificial light. Again, melatonin production shut down when the bright lights went on. These findings were published in the December 12, 1980 issue of Science.

Dr. Harry Lynch, an M.I.T. light researcher who works with Dr. Wurtman, said Dr. Lewy’s finding should lead to a wide variety of studies examining how human physiological rhythms respond to light. He explained, ”We may be able to deliberately manipulate pineal function to achieve some sort of therapeutic good, for example, for sleep problems, deities.” Light manipulation has been used by farmers for years to increase egg laying and milk production, though without understanding how it works.

Dr. Lewy warned, however, that people should not attempt selftreatment by deliberately staring at high-intensity lights or overexposing themselves to sunlight or ultraviolet lamps lest they risk retinal burns, sunburn and damage that could lead to skin cancer.

Source: http://query.nytimes.com/gst/fullpage.html?res=980CE2DD1138F930A15755C0A967948260&sec=health&spon=&pagewanted=all

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