The positive heath effects of sunlight

A viewer is asked about blue light and its health effects.  She heard that exposure to blue light could cause insomnia and other health problems but her friends say that it is being used by doctors for depression and other diseases.  Last month the American Medical Association released a position statement calling for reducing the amount of blue light emitted from LED street lights adding to the confusion.

The light you can see is called white light and is actually made of light waves from every color of the rainbow from long wavelength low energy red waves to the higher energy short wavelength blue and violet waves.  Back in the caveman days, the sun provides exposure to all of these colors of light during the day with no exposure at night and this forms the basis of our circadian rhythm.  This impacts blood pressure and heart rate, release of hormones, and impacts mental well-being.  It gets you ready to start the day and gets you ready to sleep at night.  In today’s society, people are staying indoors more during the day and using artificial light from lightbulbs, TVs, computer screens, and smartphones at night which confuses our bodies.  If you don’t have enough exposure to light during the day it can cause or worsen depression.  This usually happens in the wintertime and exposure to light from the sun or a therapeutic lightbox in the mornings can help.  It looks like the blue light spectrum is especially good at providing these benefits. People who live at the beach and have exposure to the blue light reflected off the ocean actually have lower rates of depression.  However, exposure to light at bedtime can keep people awake and causes a number of negative health effects such as higher blood pressure, obesity, and risks of falls and accidents.  Blue light in particular can suppress melatonin release, suppress sleep inducing delta waves in the brain, and decrease the amount of REM sleep people get.  Blue light waves also cause more glare and can make it harder for people to see properly when directly exposed.  So it really is a trade-off between the benefits and risks of blue light and the time of day is a critical determinant of the long term outcome.

Being exposed to sunlight is good for your mood and helps regulate a normal circadian rhythm even in those who are blind because the receptors in the eye that send nerve signals to the part of the brain that impacts melatonin release and mood are not the same ones needed for sight.  If you have depression which worsens in the wintertime, a light box can help as long as it is not used too late in the day.  However, 30-60 min before bedtime, try not to expose yourself to light from a TV, smartphone, or tablet and keep the room dim.  If you cannot avoid these light sources, which is preferred, there are glasses that shield the eyes from blue light rays which can be helpful at nighttime, the new iOS operating system from Apple has a setting called night shift and Android has apps like CF.lumen or Twilight that shift away from the blue end of the light spectrum towards a redder spectrum at nighttime.