News & Notes

December is the month of the shortest day of the year; the day with the most darkness of all the days.  In honor of this, our Of the Month topic is darkness.  You may wonder what there is to say about darkness, and whatever it has to do with health.  Actually, I hope you do wonder that and that you'll have a different idea about darkness when we're done!  Getting around to the point of this is going to be a little roundabout, so bear with me!
Function of Dark.  I doubt we usually think of dark as having a function, but I suspect there are a number of things that come to mind when you think of "dark."  Night is probably one of the first (especially with the picture of the moon in a night sky above to lead your thinking!)  So night, then day and we make the little leap of logic to circadian rhythms.  Circadian rhythms are found in most living things, follow approximately a 24-hour cycle, are influenced by light and dark in the environment and influence physical, mental and behavioral changes in those living things - including us.  Dark plays a significant role in the setting of circadian rhythms.
A Bit of Anatomy & Physiology.  The specific place in the brain that is responsible for setting our biological clock, which is related to circadian rhythms, is called the Suprachiasmatic Nucleus (SCN).  Just about 10 years ago we discovered a new receptor cell in the eye that does nothing to help us visually see things.  (You might remember the rods and cones in the eye are the receptors that give us sight.)  These new ganglion receptor cells skip the optic nerve and go right to the SCN - giving direct information simply about how much light is coming into the eye.  This discovery spurred a great deal of speculation and further study.
   One of the things the SCN does is control the production of melatonin.  Melatonin is a hormone released by the pineal gland, probably best known for making us sleepy, but it also is involved with cycles of the female hormones and is a powerful anti-oxidant.  Melatonin production increases in the dark (usually night), and decreases with the light (usually day).  Recent studies, however, are showing that not all lights are created equal in their ability to turn off the production of melatonin.  In fact, it appears that the blue spectrum of light is most effective at suppressing melatonin. 
Logic and Speculation.  If we think about this, it makes sense, doesn't it?  Blue sky comes in the morning, it's time to get up and start our day, how lucky that blue light is best at turning down the melatonin so we can wake up and be productive!  It appears that, once again, the body is wonderfully made to interact with its environment in a healthy way.
   But then inquiring minds start to wonder other things.  What happens when we are exposed to excessive or prolonged blue light?  What other functions of the body are related to melatonin and circadian rhythms?  Are they then affected by such exposure?  Can light and/or lack of light be used therapeutically?  If so, how? 
Current Thought.  Before Edison, there was little opportunity to have excessive exposure to light.  Humans went about their business in a pretty natural day/night routine.  Lights of campfires, candles and kerosene lamps aren't overly in the blue wavelength anyway.  Another feature of pre-Edison light exposure was contrast of day/night light.  Volume of light is measured in a unit called a lux.  On a clear night, a quarter moon is about 0.01 lux and a full moon 0.027 lux.  A very dark, overcast day is 100 lux and a basic cloudy day is 1000 lux, but a sunny day in indirect light is 10-25,000 lux and in the direct light is 35-130,000 lux!  So at the least contrast - a full moon to a very dark day - 100 lux is still over 3700 times brighter than 0.027 lux.  Those were pretty clear signals through the ganglion cells to the SCN that it was time to turn the melatonin production off or on. 
   What about today?  Here's where some of the current speculation is happening.  An average American living room is 50 lux.  A well-lit office is about 400 lux.  Depending on where we live, our cities and towns are lit up much of the night - often with fluorescent lighting that may be high in the blue spectrum.  Many people spend little, if any, time outside in the natural sunlight, going from home to office and home again.  Office lux is only 8 times greater than home lux - not much contrast in comparison to Nature's contrast.  There are very few places left in the U.S. - indeed, in the world - that experience the 0.027 lux of a full moon.  Take a look at this picture of the U.S. from satellite photos:  US Light at Night   And one of the world here:  World Light at Night   Besides the nearly constant artificial lighting, is the bluish light from our computers and televisions adding to the problem? 
   There is new focus on what unintended consequences we might be experiencing from being surrounded by so much light so much of the time.  Many of them appear to be related to the decreased levels of melatonin associated with increased exposure to light.  It's easy to guess a problem with insomnia, but lower levels of melatonin have been implicated in coronary artery disease, GERD (heartburn), asthma, Alzheimer's disease, Seasonal Affective Disorder and significantly in both breast and prostate cancers.  Night shift workers have significantly higher rates of these, and possibly other, diseases.  Melatonin is currently being studied as a treatment for a number of these concerns.
SOOO, Back to Dark!  One of the ways that we can help keep our circadian rhythms normalized and melatonin levels healthy is to increase the contrast in light levels we get during the day.  First, it's important to expose ourselves to bright, natural light everyday - and early in the day if possible.  Then, we need to decrease our light exposure at night as much as possible - in other words, to get in the darkest dark we can! 
   Obvious things like turning off the TV and computer in your bedroom are straightforward, but also apply to your alarm clock.  Okay, you might not want to turn it OFF, but you can cover it up!  You don't need to see what time it is when you're sleeping anyway.  Night lights may be helpful for safety in mid-night trips out of bed, but they aren't helpful during sleep.  They are available in motion-detector models that maintain both safety in movement and darkness in sleep.
   Black-out shades or drape linings can significantly decrease the light coming through bedroom windows.  And sleep masks can also be a comfortable, inexpensive way to block out large amounts of light.  Some people who seem to be very sensitive to light may also benefit from special glasses, light bulbs and screening devices that eliminate blue spectrum light.  If you're interested in these products, check out this website:  Low Blue Lights  (I have no financial stake in this company, by the way.)
Tangent.  Besides impacting our health, I mentioned earlier that most creatures have circadian rhythms.  Why should we consider that this huge increase of light is only affecting our health?  The British Astronomical Association's Campaign for Dark Skies addresses some of these issues, as well as just being concerned that we are losing a stunning beauty of nature in a starlit sky.  Campaign for Dark Skies is their website.  For thousands of urban school children the Milky Way and the Big Dipper are as extinct as Tyrannosaurus Rex! 

I said this was a round-about story!  I honor December and its longest night of the year - even if it's hardly the darkest night anymore.  And I hope that you'll also see the value of increasing darkness in our lives.  It can improve our sleep at night and our wakefulness in the day, as well as lower our risk for disease.  And maybe consider a vacation in one of the "dark" places on the Light at Night maps linked previously, and take in a spectacular night sky while it's still available!  That has to be good for your health too!