Green Light Exposure Can Reset Body Clock

WEDNESDAY May 12, 2010 -- Exposure to green light can reset the body's internal clock and alter sleep-related hormonal responses, new research suggests.

The finding, reported in the May 12 issue of Science Translational Medicine, stems from research conducted by a team of scientists at Brigham and Women's Hospital in Boston, and builds on prior research about how the eye handles light exposure in ways that are unrelated to vision.

So-called "non-visual responses" had previously been linked to blue light exposure, the study authors noted.

In this regard, the eye's photoreceptor system located in the eye's ganglion cell layer, and distinct from the part of the eye responsible for processing sight, had been identified as a center for special cells that detect and absorb blue light, thereby triggering a shift in the viewer's internal circadian body clock.

Blue light exposure had also previously been found to prompt increased alertness by suppressing the sleep-inducing hormone melatonin.

The study authors note that such observations have led to the harnessing of blue light for all kinds of therapeutic treatments targeting a range of circadian rhythm sleep disorders, as well as seasonal affective disorder.

In a news release from the hospital, lead researcher Steven Lockley said: "Over the past decade there have been many non-FDA approved devices and technologies marketed for using blue light therapeutically, such as blue light boxes for treatment of seasonal affective disorder and circadian rhythm sleep disorders, and glasses that block blue light from reaching the eye. Our results suggest that we have to consider not only blue light when predicting the effects of light on our circadian rhythms, hormones and alertness, but also other visible wavelengths such as green light."

The finding was based on a nine-day study with 52 healthy volunteers, who were exposed to 6.5 hours per day of either green or blue light after being placed on a wake-sleep schedule that mimicked overnight shift work. The experiment was conducted in a setting stripped of all cues that might indicate time of day.

The research team found that blue light appeared to most readily stimulate changes in melatonin levels and circadian clock rhythms. However, green light was also found to be capable of provoking non-visual responses to light exposure, although the responses were not always as long-lasting.

More information

For more on circadian rhythms, visit the U.S. National Institute of General Medical Sciences.

Posted: May 2010


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