[by Tamara Sellman RPSGT CCSH for Advanced Cardiovascular Sleep Disorders Center]
The winter solstice in North America, which is described as the shortest day and longest night of the year, takes place tomorrow.
While our current meteorological winter got off to a sparkling start with the snow we encountered earlier this month, winter solstice marks what is known as astronomical winter.
At this time of year, the North Pole receives literally no solar energy. (No wonder Santa wants to travel south in December!) Even in Alabama, the days are shorter and the nights are longer.
The significance of this time of year influences more than just the holidays, however. The lower daylight we experience at the winter solstice influences the way we behave at the circadian level.
What are circadian rhythms?
Circadian (which means "about a day") defines the structure of our energy as we move about our 24-hour day. This energy level is influenced by the light-dark cycles of the planet, which shape our biological rhythms.
These rhythms are informed by certain time cues we experience: exposure to light or darkness is the main influence, but also important to our body clocks are meal times and activity levels.
Circadian rhythms can account for a number of common behaviors, such as the need to eat in the morning or to take an afternoon nap. Every cell in our body has a circadian clock, and while the brain is the circadian "center" of the body, other systems also have their own circadian synchronicity.
For instance, circadian rhythms in the digestive system exist to slow down the digestive process as we sleep so we can go without using the bathroom for eight hours.
If our rhythms are balanced, we typically fall asleep with ease at night and awaken at or around sunrise. However, many of us don't have balanced rhythms. It might be due to one very simple fact: artificial lighting extends our encounters with daylight later into the evening, delaying our desire to fall asleep.
Did you know? Our brains release an important substance, melatonin, into the bloodstream as soon as the day of light begins to dim. But with the lights on nearly everywhere we go, less melatonin is released and we are driven biologically to stay awake.
Once we go to bed, the darkness itself creates the possibility for the melatonin surge we need to fall asleep.
Conversely, cortisol is a substance the brain releases into the bloodstream upon awakening in the morning, and throughout the day, to keep us alert and awake. It remains in steady supply as long as the eyes continue to register light exposure. It's also part of the biological, or circadian, system which regulates our sleep-wake cycles.
When we struggle to find a balance between our sleeping and waking lives, we might be suffering from a circadian rhythm disorder.
How the winter solstice affects our sleep
For some, darkening days can lead to sluggish, low energy. This might be linked to seasonal affective disorder (or SAD, sometimes called winter depression), or it could be caused by poor sleep due to holiday stress or the symptoms of illnesses like the flu or respiratory viruses. If you feel especially sedentary right now, it's probably due to biology (and not a character flaw!). Mammals, in general, like to hibernate, a behavior that isn't exclusive to bears.
At the time of the solstice, we may lose touch with ordinary circadian rhythms due to the extremes of low daytime light and long evenings.
Disruptions to circadian rhythms aren't only going to cause low energy, but other very real concerns: a reduced immune system, heightened risks for car or heavy machinery accidents, injuries caused by general clumsiness, even weight gain and mood swings.
How to reset your rhythms
You may prefer to simply hibernate (though sleeping too much is not exactly a healthy lifestyle choice.) Most people, however, have full schedules and need to maximize their daytime alertness and energy even when the skies are dim. Here are a few ways you can reset your circadian system for optimal functioning during the darkest days of the year:
This could be as simple as taking a walk first thing in the morning. That direct hit of sunshine is more than adequate for a circadian reset. If you prefer an in-home option, try out light therapy. Either sit in front of a light box for 20 minutes every morning or choose one of the wearable options now available (light therapy goggles and visors allow you to move about as you get ready in the morning).
While the human body manufactures some vitamin D naturally, it needs sunlight (or artificial light via light therapy) to do so. Getting adequate vitamin D may not necessarily make you sleep better, but it can help with deficiencies that cause problems with extreme daytime sleepiness. If you find you are napping a lot during the day, this might also cut into your need for sleep at night, resulting in an unfortunate bout with insomnia. Adequate vitamin D also bolsters the immune system during flu season.
Our bodies naturally generate melatonin, but during the darkest time of year, a little boost of manufactured melatonin might help you achieve good sleep at night. Opt for the lowest dose you can find, and take it an hour before bedtime, for best results (while avoiding bright light!).
GOOD SLEEP HYGIENE
This can't be stressed enough. Good bedtime habits are one of the best ways to maintain balanced circadian rhythms. The simplest way to do so is by keeping consistent bedtimes and wake up times. Your body and brain function much better when you follow a regular sleep-wake schedule.
Keep in mind, some folks celebrate the winter solstice!
Many cultures appreciate and honor the winter solstice by lighting candles in the house at night or gathering around bonfires to defeat the coldness and darkness. For the Danish, hygge describes a practice of embracing the darkness in quiet contemplation. And one more reason to celebrate... since the winter solstice marks the longest night and darkest day of the year, every day forward will bring shorter nights and lighter days, which may be the best reason of all to celebrate!