It has quite suddenly become that time of year again when season has passed from summer to fall and the autumnal equinox is upon us. The equinox occurs twice a year when day and night are approximately equal in length across the globe. As we all learned in grade school Earth Science, the Vernal (Spring) Equinox occurs around March 20-21 in the Northern Hemisphere and the Autumnal (Fall) Equinox occurs around September 22-23 in the Northern Hemisphere. What causes the equinoxes is that the Earth’s axis is tilted at about 23.5 degrees relative to its orbital plane around the Sun and during an equinox, the Sun appears directly above the Earth’s equator, meaning neither hemisphere is tilted toward or away from the Sun. At that moment, day and night are roughly 12 hours each everywhere on Earth. The Sun rises due east and sets due west and reaches its highest point directly overhead at the equator. This marks the transition between seasons. The spring equinox is the beginning of spring in the Northern Hemisphere and the beginning of fall in the Southern Hemisphere. Conversely, the autumn equinox is the beginning of fall in the Northern Hemisphere and spring in the Southern Hemisphere. Got that…I know, you knew that, but a refresher is always helpful as time and distance from the days of Middle School extend out beyond our memories.
There is a great deal of cultural importance to the whole equinox process. Many cultures have celebrated equinoxes as times of balance and renewal. They’ve been used to mark planting seasons, harvest times, and various religious observances throughout history. The word “equinox” comes from Latin, meaning “equal night,” though due to atmospheric refraction and the Sun’s apparent size, daylight is actually slightly longer than night on the equinox. To someone like me, living on a hilltop in San Diego as I do, the changing of the seasons and the orbital path of the earth are a big part of my existence. I cannot stay in bed past 6:30 except on rare occasions. Whether I go to bed at 10:30 or midnight, I get restless by 6:30 as the sun starts filtering around the edges of the shades over my head. Today is an overcast day on the hilltop. No rain expected but 88% humidity (very rare around here). In a year like this when rainfall has been particularly light, this sort of grey day with overcast moisture is more a welcome relief than a downer. But that is beside the point. What is more relevant is that the grayness has highlighted the fact that the days are now getting shorter and there is less light filtering around those shades in the morning. One might think that would lead to more tendency to sleep in, but so far that is not the case. I was up and at ‘em in the pale light of pre-dawn at…….6:30. My circadian rhythm has overwhelmed the seasonal adjustments.
Circadian rhythm is your body’s internal biological clock that regulates sleep-wake cycles and other physiological processes over a roughly 24-hour period. Your circadian rhythm is controlled by the suprachiasmatic nucleus (SCN) in your brain’s hypothalamus (Oooooooh!….). This master clock responds primarily to light and darkness, sending signals throughout your body to coordinate various functions. That would imply that the orbital seasonal changes should bear on the circadian process. But what regulates circadian rhythm is more involved than just light and dark…at least to a point. It is regulated by sleep and wakefulness patterns (which for me are mostly governed by my joints and muscles, which only want to be prone for so long). There is also body temperature fluctuations, which mostly comes from hormone production (melatonin, cortisol, growth hormone, which I have explained I seem to have in abundance in a good way), blood pressure and heart rate (which in my case are somewhat drug-induced by my daily meds), metabolism and digestion (which run very slowly in this bulky beast of a body I inhabit), the body’s immune system functions (which so far…knock on wood…work very well in me) and cognitive performance and alertness (which we all understand are driven by over-thinking in my case).
The natural pattern of a typical circadian cycle is that in the morning, Cortisol peaks, body temperature rises, alertness increases. Then, in the afternoon you reach peak physical coordination and reaction times, with likely some bio rhythmic low in mid-afternoon to refresh. In the evening, Melatonin production begins and body temperature starts to drop so that by full-on night you can allow deep sleep to occur, allowing for tissue repair and memory consolidation to happen so that you are ready for the next day. The strongest cue for your circadian clock is light, to be sure. But things like meal timing matters and can shift certain body rhythms, as can physical activity. this is why many people like me do whatever exercise they are likely to undertake in the early part of the day. In theory, that exercise helps reinforce healthy patterns in your circadian rhythm. Research shows that age can make a big difference in circadian rhythm. Rhythms tend to shift earlier as you get older. And as we all learn more and more as we get older, genetics matters a lot. Some people are naturally early risers or night owls and there is little they can do to alter that, but rather, are wise to play into those tendencies, as I tend to.
Our modern awareness for circadian rhythm disruption tends to be very much top of mind, whether we’d call it that or not. When your circadian rhythm is disrupted (by shift work, jet lag, excessive screen time, or irregular schedules), you tend to know that you may experience sleep problems, mood changes, decreased cognitive function, and increased risk of various health issues including diabetes, obesity, and cardiovascular disease. Maintaining consistent sleep and wake times, getting morning sunlight, and limiting evening blue light exposure can help keep your circadian rhythm synchronized. And then all that theory and understanding go out the window when I am lying in bed at 6:30 with no light coming around the shades and my jumpiness makes me get pout of bed for no particular reason that I can comprehend. Sometimes its to get a jump on an early shower, sometimes its to check on an incoming email from Europe or NY. Sometimes its because I’ve been dreaming about planting this or that and want to just get on with it. This morning it is a hodgepodge of all of that and is in no way specific to any great angst in my soul. So I sit here in the dark (in truth it is far less dark now) and write about sitting in the dark in hopes that it will help me explain to myself why I am the way I am. And then Popeye once again pops into mind and I remember that I “yam what I yam and that’s all that I yam”.