Seeing the Light of Day

 The counseling center at the University of Washington in Seattle offers light therapy.
The counseling center at the University of Washington in Seattle offers light therapy. (Blaine Harden/twp - Blaine Harden The Washington Post)
By Rick Weiss
Washington Post Staff Writer
Tuesday, October 30, 2007

Oh, the light! The autumn light! Is there anything more glorious than an October 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.

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 (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, and 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.

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