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Time Change Takes Extra Toll

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By RICK WEISS The Washington Post

Published: November 4, 2007

Oh, the light! The autumn light! Is there anything more glorious than a fall 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 a.m. is now 5.

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.

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 in December 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 such toxic chemicals as trichloroethylene, vinyl chloride and polychlorinated biphenyls (PCBs).

"Electric lights are wonderful, but as with a lot of other things, we really mess things up," said David Avery, a psychiatrist at the University of Washington School of Medicine who studies light's impact on health. "Our ancestors evolved in a very regular light-dark cycle, and our bodies just work better that way. But more and more, we are creating very irregular, erratic lighting cues."

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.

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, then fall before dawn in advance of awakening.

Rats whose SCNs are surgically removed become unhinged from time, sleeping at odd intervals. And when one animal's SCN is transplanted into another's brain, the recipient takes on the donor's wake-sleep schedule.

But the SCN does not work in a vacuum. It takes cues from light signals sent 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 light needed to get them firing is about 500 billion photons per second per square centimeter, or the intensity of sunlight reaching the eye at about daybreak. 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.

Night Owls And Larks

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.

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 worsen in winter, blossoming into what is in effect a monthslong 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 timing of the brain's melatonin production.

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

Recent work by Thomas White of the New York State Office of Mental Health and Michael Terman, director of the Center for Light Treatment and Biological Rhythms at Columbia University Medical Center, has shown that seasonal depression and mood disorders become more prevalent not only at northern latitudes - not surprising, as days are shorter there - but also toward the western edges of time zones, where people remain in darkness almost an hour later each morning.

Daylight saving time, which was stretched this year to today for a number of reasons, including an effort to save energy, exacerbates the problem by further delaying the time of sunrise, a key signal that resets the body's clock each day.

"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."

See The Light For Treatment

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

For most people with SAD, the trick is to get bright light exposure first thing in the morning to simulate an earlier dawn and shift the body clock forward, said Alfred Lewy, a psychiatrist and chronobiologist at Oregon Health & Science University in Portland.

For some people, taking 0.3 to 0.5 milligrams of melatonin in the midafternoon also can help, he added.

For the minority of SAD sufferers who are larks, light in the early evening can help.

Diagnosing yourself as owl or lark can be tricky. Wake-up times are affected by much more than your natural clock (whether your sixth-grade daughter has to be fed before trudging off to school in the dark, for example), so your sleep schedule is not a surefire clue. Lewy suggests trying morning light first, but switching to the lark regimen if symptoms worsen.

Many kinds of lights are available for SAD treatment. Although some experts recommend those rich in the sky-blue wavelengths (the color that ganglion cells respond to), others warn that intense blue light can damage the eye. Most research indicates that 30 to 90 minutes' exposure to fluorescent "white" lighting of about 10,000 lux works fine.

So effective is light as a mood improver that many psychiatrists now suspect that their understanding of depression has been backward: The disturbed sleep and withdrawal into darkened rooms so often seen in patients with depression, bipolar disorder and related problems may be not a symptom of those diseases but a cause. Reset the clock, and the depression lifts.

A 2005 review commissioned by the American Psychiatric Association concluded that daily exposure to bright light was about as effective as antidepressants against several forms of depression. Recent studies have suggested light therapy also can help patients with Alzheimer's disease.

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.

Richard Stevens, an epidemiologist at the University of Connecticut Health Center in Farmington, 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 percent 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 anticancer hormone.

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

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