© 2001Pro Health, Inc.,

Immune Support.com

August 17, 2001

Scientists Discover Key to Melatonin Production

and Regulation of Circadian Rhythms

________________________________________________________________________________________________________________

________________________________________________________________________________________________________________

N

euroscientists at Jefferson Medical College have

clarified how the human eye uses light to

regulate melatonin production, and in turn, the

body's biological clock. Their observations are

published in the August 15 issue of the

Journal of

Neuroscience.

The scientists discovered what appears to be a fifth

human "photoreceptor," which is the main one to

regulate the biological - and non-visual - effects of light

on the body. They have identified a novel photopigment

in the human eye responsible for reacting to light and

controlling the production of melatonin, which plays an

important role in the body's circadian rhythms. They

also discovered that wavelengths of light in the blue

region of the visible spectrum are the most effective in

controlling melatonin production.

"We have strong evidence for a novel, fifth

photoreceptor and it appears to be independent of the

classic photoreceptor for vision. It influences the

biological effects of light. It regulates circadian rhythms

and hormones in the body. We've also shown the

fingerprint of wavelength sensitivity for the regulation

of the hormone melatonin," said

George Brainard, Ph.D., professor of neurology at

Jefferson Medical College of Thomas Jefferson

University in Philadelphia.

"This discovery will have an immediate impact on

the therapeutic use of light for treating winter depression

and circadian disorders," he adds. "Some makers of light

therapy equipment are developing prototypes with

enhanced blue light stimuli.

Four cells in the human retina capture light and form

the visual system. One type, rod cells, regulates night

vision. The other three types, called cone cells, control

color vision. It's known that exposure to light at night

can disrupt the body's production of melatonin, which is

produced by the pineal gland in the brain and plays a

vital role in resetting the body's daily biological clock.

Earlier this year, Dr. Brainard and his group showed

that the combined three-cone system didn't control the

biological effects of light, at least not for melatonin

regulation. But subsequent work led to the surprising

discovery that a novel receptor was responsible for the

effect.

"We didn't anticipate this at all," he says.

In the study, they looked at the effects of different

wavelengths of light on 72 healthy volunteers, exposing

them to nine different wavelengths, from indigo to

orange. Subjects were brought into the laboratory at

midnight, when melatonin is highest. The subjects'

pupils were dilated and then they were blindfolded for

two hours. Blood samples were drawn.

Next, each person was exposed to a specific dose of

photons of one light for 90 minutes, and then another

blood sample was drawn. Wavelengths of blue light had

the highest potency in causing changes in melatonin

levels, he explains.

In theory, he says, "If a clinician wants to use light

therapeutically, the blue wavelengths may be more

effective. If you wanted built-in illumination that would

enhance circadian regulation, you might want this

wavelength region emphasized. In contrast, if you

wanted something that doesn't produce biological

stimulation, you might steer the light more toward the

red wavelengths." But controlled clinical trials will be

needed, he adds. Next, Dr. Brainard's team would like to

study the next step in how light regulates not just

melatonin, but all of the body's circadian rhythms,

including body temperature, cortisol and performance

rhythms. The National Institute of Neurological

Disorders and Stroke, the National Space Biomedical

Research Institute and NASA funded the research.