Understanding the science of circadian rhythms.
Your environment controls your body's activity—here's how.
This is a science-based newsletter, but at the same time, lifestyle is not science. So, what science do you need to understand for this circadian rhythm stuff to make sense? In today's post, I'm going to give an overview of the science of circadian rhythms.
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This is the best graphic I have been able to find so far. It shows the 2 primary zeitgebers—that is, time-givers. Light and food. To be even more accurate, we could say the light/dark cycle and the food/fast cycle.
These alternations control what happens in the brain, which then control the body. What kinds of things do light and food control? Pretty much everything! But one example that is often used as a marker of overall rhythmicity is melatonin. Melatonin can only be synthesized in darkness. So, if you are like most in the US (99%), you experience so much light at night your body can't make enough melatonin. This is only one example of circadian disruption.
Metabolism is also under circadian control. Like lacking time under darkness, we also tend to lack time without food in our system. We need time without active digestion going on so that we can undergo a process called autophagy.
Autophagy is the process of breaking down old cells, pathogens, and waste products. It should happen every night while we sleep. If it doesn't, we see metabolic problems like being overweight and/or having type II diabetes. In research, scientists talk about “temporal compartmentalization.” This is a scientific way of saying certain processes can’t happen at the same times. We know we can’t be awake and asleep at the same time. Digestion has functions that are like that, too. Here’s a graphic showing in layman’s terms what happens when you eat after dark:
From these two examples, we can see how different life can be with and without a proper nighttime darkness and fast.
And these are only two of many functions that rely on alternating signals from day/night.
All these words describe how our bodies turn cues like brightness and meal timing into instructions. So, the main part of the body we talk about is the suprachiasmatic nucleus, or SCN. (That is what the first graphic in this email shows).
Here is another depiction of the SCN I like because it shows that it responds to both light and dark:
So, if it is bright, the SCN receives the light signals and tells the body to run daytime processes. If it is dark, the SCN receives the darkness signal and tells the body to run nighttime processes.
That alternation between two sets of activities is what we mean by "circadian." If we live only in light, or only in darkness, we are missing out on half of our biological function. And that is what we mean when we say "disruption." The cycle of light/dark is disrupted.
If light was balanced between 6am and 6pm, and here's approximately what that would look like in the body.
Since light is not perfectly balanced across the year, processes will vary. Sadly, we do not have a whole lot of research at this point about how rhythms vary across the year and with the seasons. Some "experts" even go so far as to say humans should only live within 30 degrees of the equator! I disagree. In case you missed it, I wrote a post earlier this year about how the Eskimo Inuit used to deal with the endless summer sun:
And I am always on the lookout for more information like this. Do you live at an extreme latitude? Do you have any experiences with feeling your body rhythms change across the year? Let us know in the comments!
That's all for today, but you can always review past posts at brighterdaysdarkernights.com/archive.
Brighter Days, Darker Nights is a reader-supported publication. To receive new posts and support my work, consider becoming a free or paid subscriber.