Artificial illumination can mess with more than your mental health

by Newspartnergroup | November 7, 2007 at 04:38 am

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Oh, the light! The autumn light! Is there anything more glorious than a November day, awash in the sun's low-slung amber rays?

And yet ... perhaps you feel the dread, too. The looming inkiness that, like the tide, crawls up your legs a little higher each day, turning that honeyed light to molasses and molasses to muck until you realize, too late, that the birds have left and the world has gone dark. Dark when you wake up, dark when you go home.

In simpler times we slept more in winter, but modern living denies us that luxury. So increasingly each day, soft-white lights from yonder windows break — along with halogens, tungstens and compact fluorescents. And when we can't stand it anymore, we resort to manipulation, declaring that 6 in the morning is now 5.

You got a problem with that, take it up in the spring.

Now science is finding that our manhandling of light and time is making us sick.

Artificial illumination is fooling the body's biological clock into releasing key wakefulness hormones at the wrong times, contributing to seasonal fatigue and depression. And daylight-saving time, extended by Congress this year for an extra four weeks, risks dragging even more Americans into a winter funk.

MORE ILLNESS

Much more than mental health is at stake. Women who work at night, out of sync with the light, have recently been shown to have higher rates of breast cancer — so much so that an arm of the World Health Organization will announce next month that it is classifying shift work as a "probable carcinogen."

That will put the night shift in the same health-risk category as exposure to some types of toxic chemicals.

"Electric lights are wonderful, but as with a lot of other things, we really mess things up," said Dr. David Avery, a psychiatrist at the University of Washington School of Medicine who studies light's impact on health.

Researchers have long known that virtually all living organisms have biological rhythms that are linked to light. But the human health implications remained opaque until the 1970s, when scientists discovered the brain's internal clock: the suprachiasmatic nucleus, or SCN, a tangle of neurons in the hypothalamus connected directly to the eyes.

HORMONES AFFECTED

The SCN controls the ebb and flow of hormones that influence sleepiness, alertness and hunger. Prime among them is melatonin, levels of which rise each evening, easing the onset of sleep, and then fall before dawn in advance of awakening.

But the SCN does not work in a vacuum. It takes its cues from light signals passed along by the eyes.

For decades scientists presumed that those clock-setting signals came from rods and cones, the light-sensitive cells in the retina that provide black-and-white and color vision. Then, in 2002, researchers at Brown University discovered an entirely different set of light-detecting cells in the eyes of humans and other mammals: ganglion cells.

Unlike rods and cones, ganglion cells specifically detect sky-blue light. The amount of light needed to get them firing is the equivalent of the intensity of sunlight reaching the eye at about daybreak. Taken together, those traits make them the perfect cells to tell the brain when dawn has arrived, which they do via a dedicated neural conduit to the SCN.

Unfortunately, this system does not always work like clockwork.

Because of genetic differences, many people's clocks are set differently from others'. In some, the evening melatonin spike is delayed and sleep comes late. Early awakening is also often difficult for these night owls, perhaps in part because their melatonin levels have not had time to drop sufficiently by morning.

Others have the opposite problem: The clocks in these morning larks run fast compared with solar clock time, lulling them to sleep early and then awakening them well before dawn's early light.

Being out of phase with the natural day-night cycle can take a big toll, causing fatigue, mood disturbances and depression. But for millions of Americans, these symptoms become even worse in winter, blossoming into what is in effect a months-long case of jet lag.

Scientists disagree on the cause of seasonal affective disorder, or SAD, as it has come to be known. Some focus on winter's late sunrises, which appear to push various hormone cycles out of phase with the daily wake-sleep cycle. Others focus on the early sunsets, which may affect the timing of melatonin production in the brain.

But while genes clearly play a role (night owls are more often affected), location also matters.

Daylight-saving time was stretched this year to Sunday for reasons that include an effort to save energy. But the change exacerbates the problem of seasonal depression and mood disorders by further delaying the time of sunrise, a key signal that resets the body's clock.

"From the psychiatric perspective, the extension of daylight-saving time this year was a very bad decision," Terman said. "Our expectation is we will see increased depression and mood disorders."

The good news is that treatments for seasonal depression — primarily the use of bright light, and in some cases melatonin supplements, to reset the body's clock — can be effective.

LIGHT NEVER LEAVES

Of course, the fact that artificial lighting can reset people's clocks and boost alertness at night speaks to its potential to throw normal rhythms into disarray. As though it were not bad enough that lighting is a 24-7 feature of modern life, said Avery of the University of Washington, people spend evenings staring at their "Microsoft blue" computer monitors, then wonder why they can't fall asleep.

"We've deseasonalized ourselves," said Dr. Thomas Wehr, a psychiatrist at the National Institute of Mental Health in Bethesda, Md. "We are living in an experiment that is finding out what happens if you expose humans to constant summer day lengths."

The perfect solution, as any camper knows, is to give up artificial light, an approach that quickly brings one into a cycle of long, restful nights and easy awakenings at dawn. More realistically, experts recommend avoiding bright lights after dusk and perhaps wearing yellow sunglasses at brightly lit evening events to filter out the blue light that might fool your ganglia into thinking it is morning.

For those working at night, "the idea might be to have a work environment where at the beginning of the shift the lighting is heavier in blues that suppress melatonin, then gradually it changes and becomes redder and redder," a hue that does not stimulate the eye's ganglion cells, said Richard Stevens, an epidemiologist at the University of Connecticut Health Center in Farmington.

Stevens knows how important night-shift lighting can be. It was his focus on the issue that helped reveal that women who work night shifts for 20 to 30 years have breast cancer rates 30 to 80 percent higher than their day-shift counterparts. The mechanism is still not fully explained, but studies have since shown that melatonin — whose secretion is suppressed by nighttime illumination — is a potent anti-cancer hormone.

Consistent with that, profoundly blind women also have very low rates of breast cancer, presumably because their melatonin levels are never suppressed by light.

A panel of experts convened this month by the International Agency for Research on Cancer, part of the World Health Organization, reviewed studies on animals that were kept awake at night or subjected to repeated six-hour jet lags, and several large human studies of nurses and airline flight attendants. It concluded there is strong evidence that shift work can cause cancer.

Darkness doesn't have to be about depression and loneliness, said Dave Crawford, executive director of the International Dark-Sky Association, a Tucson-based nonprofit group that advocates against unnecessary illumination.

It can be about stars, about contemplation, about quiet conversation with a friend.

"If we sprayed water all over the place here in the desert, we'd be put in jail. So why is it OK to spray light all over the place at night?" asked Crawford, adding that more than half of all mammals spend most of their waking hours at night or twilight, "including teenagers."

Light is fine — in the day — Crawford said. "We're trying to bring to everyone's attention that there is a night."

For the next few months, that is going to be hard to forget.

Source: http://www.thefitnessclub.info