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Shining Light May Shift Sleep Cycle

January 16, 1998

WASHINGTON (AP) _ Applying light to the back of the knees is just as effective in resetting the sleep-wake cycle as shining lights into the eyes, researchers say.

A Cornell University researcher said Thursday experiments showed that the body clock, which controls the sleep-wake, or circadian, cycle can be change by shining a bluish light on the tender skin back of the knees at specific times during the day.

``We got the same type of clock resetting with this as others have by shining lights into the eyes,″ said Scott S. Campbell of the Cornell University Medical College in White Plains, N.Y.

It has long been believed that the natural body clock, which controls wakefulness and sleep, is controlled by the amount of light falling on the eyes. Some shift workers and jet travelers routinely reset their body clocks by sitting in front of bright lights for a time.

But Campbell said it may not be necessary to look at the lights.

His study with 15 volunteers showed that shining light for up to three hours on the back of the knees also caused a shift in the body clock.

Campbell said the clock shift was detected by taking the volunteers’ temperatures and measuring the level of melatonin in their saliva. Melatonin is a hormone that is secreted in phase with the body clock.

Normally, the natural clock causes the body temperature to start falling during the evening hours and then to rise just before dawn. Melatonin levels are a mirror image, going down during the day and then rising during the night.

By applying light to the back of the volunteers’ knees, said Campbell, he could cause the body clock to shift forward or backward, depending on when the light is applied.

For instance, in one 44-year-old man, applying lights to the knees for three hours, from 6 a.m. to 9 a.m., caused the body’s temperature minimum to shift from 7 a.m. to 4 a.m.

Campbell said that such techniques would be useful in helping night shift workers change their sleep-wake cycles to meet the needs of the job.

The technique could also be used to combat jet lag, he said. For instances, said Campbell, a passenger could expose his legs to light at a carefully planned time while flying to Japan and ``he could have his body clock reset by the time he got to Tokyo.″

This would avoid jet lag, the listless exhaustion caused by flying across many time zones within a short period.

The study is being published Friday in the journal Science.

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