Every evening, the hormone melatonin activates sleep and other nighttime processes in our bodies. Melatonin is a primary contributor to our health.
Exposure to blue wavelengths of light during evening hours (or pre-sleep hours for shift workers) suppresses the release of melatonin and disrupts sleep (especially restorative sleep) and circadian rhythms.
This blue wavelength sensitivity cannot be explained by the spectral sensitivity of the rods and cones in our eyes. For over a hundred years we have known that daytime color vision relies on cone receptors that provide color information to the brain. While the cones can respond to all colors in the visual spectrum, they are most sensitive to green light. Nighttime vision is dependent on rod receptors that can see even when light levels are very low. The pathways that carry visual images from the rods and cones to the brain have been well mapped and understood. But neither rods nor cones are highly sensitive to the blue wavelengths that reset circadian rhythms and suppress melatonin.
The important discovery, which explained the blue light sensitivity, was the identification of special types of photoreceptor cells in the retina containing melanopsin, a photo pigment with a peak sensitivity to 460nm blue light. The melanopsin receptors are 25 times more responsive to light at this blue wavelength than to full spectrum white light. When activated by blue light, the melanopsin receptors send information via a special neuronal pathways directly to the suprachiasmatic nucleus (SCN) in the brain. These melanopsin pathways are quite separate from those that carry visual images to the brain. The SCN is the body’s “master circadian biological clock.” It thus became clear that, just like our ears have the two functions of hearing and balance, our eyes have the two functions of seeing visual images and regulating the brain’s master circadian clock.
Natural night after sunset is associated with the absence or very low levels of bioactive blue light content. The lack of blue light provides a night signal to the master clock and triggers a chain reaction that activates hormonal and other pathways critical to maintaining health and avoiding depression, diabetes, obesity, cardiovascular disease, and breast and prostate cancer. Around 9 PM melatonin secretion starts to climb and this a critical signal that circadian night has begun. Body temperature is lowered, and bowel movements are suppressed.
Melatonin secretion peaks around 2 AM, then starts to drop and terminates by 7 AM, signaling the start of a new day. Just as the presence of bioactive blue light is critical to maintaining circadian day functions, the absence of bioactive blue is critical to maintaining optimal circadian night functions.Download Medablu Blue-free white paper