RESEARCH SHOWS THE EFFECTS OF LIGHT ON MELATONIN PRODUCTION
Melatonin is the sleep hormone produced naturally in the human body by the pineal gland in the brain.
Tests have now conclusively proven that different light wavelengths have different effects on the body’s melatonin production.
In a test performed in 2001 by Debra Skene at the University of Surrey, light was shone into volunteers’ eyes in the middle of the night, when melatonin production levels are at their peak. Melatonin production was found to be clearly sensitive to light: production levels decreased as light intensity increased. However, what was interesting was that the different wavelengths of light produced different results. The shortest wavelengths, what we see as dark blue, caused the greatest drop in melatonin. What is particularly interesting is that the rods and cones in the retina barely detect this wavelength of light.
"Skene concluded that there must be a third, still unknown type of photoreceptor that tells the brain when to stop making melatonin"
A further study in 2002, by David Berson of Brown University, went on to confirm that a new type of photoreceptor existed. Berson described them as a type of retinal ganglion cell. These cells extend long projections into a part of the brain called suprachiasmatic nucleus (SCN). They transmit information directly from the eyes into the region of the brain that regulates the circadian clock These photoreceptors are the sensor in the pineal gland that receive the blue light, which signals to the pineal gland to stop producing melatonin.
What these tests found was that there are two completely separate systems in operation in our eyes. One, using rods and cones, allows us to see things. The second controls the release of melatonin. The photoreceptors receive information directly from the eye to the part of the brain that regulates our body clock, or circadian rhythm.
In 2003 it was confirmed by Lockley et al that the shorter wavelengths of light have a greater effect on melatonin production. The short 460 nanometres (nm) wavelengths of light suppress melatonin twice as much as longer 555 nm light, the wavelength best seen my the human eye.
"It was demonstrated that if we can control the wavelengths of light reaching the eye, we can control our internal clocks"
In 2005 Christian Cajochen at University Basel in Switzerland, successfully reset the circadian clocks of test subjects through the use of colored lights. Test subjects were exposed to indigo-blue light with a wavelength of 460 nm, green-yellow light with a wavelength of 550 nm, or complete darkness. The researchers then monitored each subject’s sleep / wake cycle. Subjects in complete darkness showed normal nighttime trends of reduced core-body temperatures, slower heart rates, higher melatonin production and increased sleepiness. Exposing subjects to the indigo-blue light suppressed melatonin production and other normal nighttime trends. Green-yellow light had a minimal effect.
In 2007 a further study by Farhan Zaidi et al, at the imperial College London concluded that there are two separate functional light sensing systems in the eye: one for vision, and one for setting our sleep / wake pattern. Blind people who lack rods and cones in their eyes but still have functional blue light sensitive ganglion in their eyes were still able to unconsciously sense whether it was light or dark by detecting blue light. By shining a light in their eyes, the researchers were able to delay the subjects’ body clock cycle, proving that their ganglion cells still registered light. The blue light caused melatonin production to drop by 60%, while at the same time alertness sharpened and brain activity increased, demonstrating that the body clock had been tricked into thinking it was daytime.
The wavelength of 480 nm which the retinal ganglia are so sensitive to, is in the blue spectrum. In fact, it is very similar to the color of the sky on a bright sunny day. Bright lights, especially blue lights, tell our brain that it is morning.
Conversely, when the sun is setting the eye sends signals to the brain that night is falling, which activates the pineal gland to produce melatonin. Melatonin then works to induce feelings of drowsiness, acting as the signal to the body that it’s time for bed.
- ^ Escrivá, JosemarÃa (1939), "Number 206", The Way
- ^ Thurber, James (31 Mar 1983). Fables for our time (Rei Ill ed.). HarperCollins. ISBN 978-0-06-090999-4. Unknown parameter
|illustrator=ignored (help) - ^ "Teen sleep: Why is your teen so tired?". Mayo Clinic.
- ^ "Later start times for high school students". University of Minnesota College of Education and Human Development. June 2002.
- ^ "School Start Time and Sleep". National Sleep Foundation.
- ^ O'Callaghan, Tiffany (2010-07-06). "Study: teens benefit from later school start". Time.
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