Story last updated at 1/18/2012 - 12:59 pm
We're gaining daylight at an increasing pace since winter solstice, but we're still in the heart of winter when low light levels influence mood and sleepiness for many. It is common knowledge, supported by medical research, that exposure to a strong source of blue or full spectrum light can boost energy and improve mood. But why?
Light therapy has been of medical interest for centuries and many pre-modern hospitals included a solar room for patients. However, only in recent decades is the physiochemical basis of light's effects on mammals beginning to be understood. Here, we will explore an example of how light affects a biochemical process important for mood and sleep-wake cycles. In doing so, we can gain insight as to how non-light mood enhancers may work through a similar mechanism.
The human circadian rhythm is a daily cycle of biochemical, physiological and behavioral activity that can be influenced by environmental factors. In addition to the daily rhythm, there are also other time levels of synchronization - for example, monthly menstruation. Chronobiology, the study of biological timing, is a very active area of current research with a lot of open questions. However, we do know that biological clocks can be influenced by factors called zeitgebers. Zeitgeber is German for "time giver" or "synchronizer." Although light is the strongest zeitgeber, other factors such as exercise, social interactions, pharmaceuticals and eating/drinking patterns can influence our daily cycles.
An example of how light can affect our mood and sleep wake cycles is provided by the neurohormone melatonin, affectionately called the "hormone of darkness." Melatonin acts largely in the brain, where it binds to the melatonin receptor leading to downstream effects including sleepiness and improved mood. Experiments have shown that waking people at night, when peak melatonin production occurs, and shining light in their eyes strongly decreases melatonin production. So, the absence of light is a cue for increasing melatonin biosynthesis. Melatonin is also a powerful antioxidant, scavenging free radicals that may otherwise damage healthy tissue, and therefore may also influence regeneration during sleep.
Not any light will do. Only light that includes blue-green wavelengths can cause this effect on melatonin production and regulation of the circadian rhythm. Full spectrum light, such as light from the sun or specialized bulbs, is made up of many different colors although it may appear white. Think of how a prism splits a sunbeam into a rainbow. The connection between blue light and circadian rhythm regulation is provided by a protein called cryptochrome, Greek for "hidden color." Cryptochrome is a key photoreceptor protein present in our eyes, which is activated by blue light. Once activated, cryptochrome works together with other circadian regulator proteins to influence whole networks of gene expression in addition to inhibiting melatonin production.
An article published in the molecular biology journal "Genes to Cells" in 2010 added a key piece of information linking blue light to melatonin. Utilizing mice with a defective cryptochrome gene, researchers discovered these mice did not decrease melatonin production when exposed to bright light during their sleep cycle. When cryptochrome was lacking, the light signal could not be processed and the mice continued to produce high levels of melatonin. This strongly suggests cryptochrome is necessary to relay the signal, which results in decreased melatonin production.
Let's relate this result back to our experience with lights that emit the crucial wavelengths, commonly called happy lights. Say you wake up and it's still dark outside. Your melatonin production is still quite high and you feel sleepy. You decide to use your happy light and this induces a rapid decrease in melatonin production and leads to a feeling of wakefulness. You feel better and go about your day. Additional studies have used melatonin as a therapeutic agent in coordination with light therapy for improved outcomes in treating seasonal affective disorder.
The blue light-melatonin connection is perhaps the most clearly understood example of a zeitgeber affecting a biochemical process, and illustrates how an environmental factor such as light can change our biochemistry. However, it is certainly not the entire story. Above, it was mentioned that cryptochrome influences whole networks of genes, and in fact more than one-third of active genes have shown to be regulated differently from day to night. Perhaps this gives some insight into the importance of sleep, when our bodies switch into a whole different mode.
Taking the night concept to the extreme, it might be argued that winter is one big night when our bodies can do large-scale rest and regeneration, allowing deeper metabolic and perhaps psychological digestion of the year past and recouping for the year ahead. Maybe it's more the expectation that we should not slow down and should adhere to modern schedules that can lead to depression when our bodies don't comply. One report states Native Alaskans living above the Arctic Circle do not experience nearly as much seasonal affective disorder we might expect, and gives credit to honoring nature's cycle and taking rest. Why not embrace the darkness and allow some inner retreat - honoring nature and her wisdom? The bears do it and plants do it, or they at least slow way down.
This winter I choose to not use a happy light and instead tapped into some of the other zeitgebers: Taking exercise, quality time in community and consistent meal timing. Thankfully, I have maintained an early waking time without using an alarm, and have felt pretty energetic. Light from a friend's smile or metabolically lighting up our engines through exercise can have the same effect on mood as blue light. Imagine your physiology changing after a daytime walk with a friend followed by lunch. Nevertheless, light therapy is the strongest zeitgeber and it's exciting that new research is beginning to show us how these effects are mediated. As always, the hope is that more information can lead us to better solutions.
For more information, can be found here.
Jasmina Allen currently lives in Juneau and holds degrees in chemical biology. She may be reached at jsmnallen@gmail.com.
