Expose Yourself to the Light, Be Happy

I know spring is here when I see the kid down the road wearing shorts as he waits for the school bus. He suffers on cold mornings, but the lad may be on to something--news from back east is changing researchers' ideas of how light effects the human body.

Bright light applied to the back of people's knees has had an effect similar to that experienced by people who gaze at special light tables to combat seasonal affective disorder. Scott Campbell and Patricia Murphy of Cornell University Medical College in White Plains, New York, have found this unique treatment has allowed them to reset the human internal clock. Their research may lead to different treatments for seasonal affective disorder, a common malady among northerners who in the dark season find themselves more irritable, sleepy, and hungry.

In Campbell and Murphy's study, they tinkered with people's circadian rhythms--the body's synchronization to Earth's 24-hour rotation that gets out of whack when people fly across a few time zones. Researchers have found that people develop cycles of waking, sleeping and body-temperature changes even if those people aren't exposed to sunlight. For reasons scientists don't quite understand, these cycles are slightly longer than 24 hours, but less than 25 hours.

Sunlight and darkness are two of the signals we use to reset our internal clocks every day. Without being conscious of the signals' effect, we use daylight, dark nights and even the morning commute to work to get in tune with a 24-hour day. As a result of that tuning, our body temperatures drop several degrees while we sleep.

Campbell and Murphy monitored the body temperatures of 15 volunteers who slept in a lab. The researchers woke the men and women at different times of the night and told them to sit up while the researchers attached an illuminated pad to the back of the volunteers' knees. When the pad was lit just before the subjects' lowest body temperature was reached (about 5:30 a.m.), the individuals' daily rhythms were delayed by three hours the next night. A three-hour shift the other way occurred when the light was shined behind the knee just after the body reached its lowest temperature.

The results of the study challenge the assumption that humans fine-tune their internal clocks with light that enters the body solely through the eyes. Campbell and Murphy even tried applying light to the back of the knees with a light table used by sufferers of seasonal affective disorder. Once again, the internal clocks of the volunteers were reset.

Campbell and Murphy chose to apply light to the back of people's knees for two reasons: they were looking for a site that prevented light from reaching the eyes of the subjects, and the tender skin on the back of the knee has many blood vessels near the surface. Campbell said the researchers wanted to test a hypothesis of Dan Oren, a psychiatrist who specializes in circadian rhythm disorders at Yale University. Oren believes blood may be the messenger that carries the light signal from skin to the brain.

Though skin blocks or absorbs most light, some passes through, Oren said. He and other researchers are now exploring whether the light that gets beneath our skin may produce gases in the blood or destroy blood pigments, both of which may affect a person's internal clock.

Campbell said he and other researchers are interested in inventing a portable light that a person might be able to wear behind the knee while traveling to reduce the effects of jet lag. A similar device might also have potential for treating seasonal affective disorder. Maybe Alaskans should expose some of that pasty winter skin. Get out your glacier glasses.