To every thing there is a season, and a time to every purpose under heaven. (Ecclesiastes 3:1)
Many refer to the body as having some type of “clock.” When certain parts of the country change to Daylight Savings Time or when we cross time zones in our travels, for example, we complain that it throws off our “internal clock.” When we discuss life chapters such as those defined by childbearing or retirement, we refer to a “biological clock.” A newborn infant who cries for feeding at 3 a.m. is a prime example of one whose timing hasn’t yet been conditioned to life outside the womb. When we refer to our bodies having some sort of internal timing mechanism, we’re closer to accuracy than even we realize, yet many don’t recognize the name of the most important internal clock that we have: circadian rhythm. Further, to say that the body has a built-in timekeeper may give the impression that this mechanism merely regulates when we wake up, become hungry, and go back to sleep. But, it does so much more; it controls the entire functionality of our physical makeup. And, it embodies one simple truth that many of us don’t realize: The timing of our bodily systems is often just as important—if not more so—as what we actually do with our bodies. While the circadian rhythm is often overlooked or taken for granted by people going about their daily lives, there are vast ways it is vital to our overall health.
What Is Circadian Rhythm?
The word “circadian” is generated from the roots circa (“around”) and dian (or diam, “day”).[i] So the concept refers to a cycle in which our body is meant to work “around the day.” This is an internal clock that is active for the entire twenty-four-hour period. For the human body, the clock is divided into three segments wherein the activity is geared toward a specific theme: sleep, nutrition, and activity. Almost every gene, hormone, and biochemical mechanism turns on and off at different times of the day. These genes govern nearly every aspect of our lives, like inflammation, energy, sleep, memory, and healing, just to name a few. All aspects of our DNA are woven into this internal timekeeper, which is synchronized through a paired group of neurons in the hypothalamus. This master clock in the brain is called the suprachiasmatic nucleus (SCN), a tiny cerebral feature that is made up of a whopping twenty-thousand brain cells, and which is set to respond to light signals relayed via the protein melanopsin, which is located within the retina of the eye.[ii] The SCN is located above the optic nerves that cross at the center of the brain. It keeps tabs on the light signals brought in through the eyes and discerns which type of light it is seeing. Depending on the type of light it’s picking up on, it sends cues throughout the body regulating appetite, motivation for activity, hormone generation and secretion, body temperature, and even moods. Surprisingly, even blind people are able to pick up enough light sensation to keep the SCN informed.
The circadian cycle is an innate feature that has evolved across the centuries to preserve our ability to hunt, gather, work, and remain vigilant during the waking hours of the day. In a (hypothetical) world in which there is nothing to interrupt it, here’s a basic idea of how circadian rhythm works:
In the morning, sunlight (often referred to as “blue light”) comes peering through the windows, filtering through the melanopsin light sensors in the retina. The eyes process these rays toward the SCN, which alerts you to the fact that a new day has begun. The pineal gland then dispatches hormones such as cortisol to cause you to rise. The pancreas is on standby, ready to dispatch the insulin necessary to metabolize breakfast. At around 9 a.m., testosterone and attentiveness should reach their peak, providing you the strength and energy you need to face the work day ahead. Shortly thereafter, your physical coordination escalates and cardiovascular strength increases. (These are adaptations that have formed over years of mankind’s need for the great manual labor known by our ancestors.) During the first half of the day, your body is in the segment of the cycle that leans toward nutrition. During these hours, insulin levels are healthiest and food is processed best. This is the when that the system is most efficient about pulling nutrients out of the food that’s been ingested. Similarly, bowel movements often happen in the first half of day, the body having conducted its own detox-and-purge process during the night. By about noon, your mental function is at its height, and after this stimulating period of time, your physical body becomes its sharpest in early- to mid -afternoon. By evening, your blood pressure reaches its high point, as the body begins to prepare for its nightly detox regime, which takes place during sleep. In response to this heightened blood pressure, your body temperature spikes at around 7 p.m. As your activity diminishes and blue light decreases and eventually disappears, the body eliminates chemicals that foster alertness. Melatonin kicks in at around 9 p.m., causing you to become sleepy. By about 10 p.m., sleep sets in, and by 2 a.m., you should be experiencing the deepest sleep of the night. During this time, your brain is processing, storing, and filing memories of events that took place during the day. The brain is likewise conducting a mass detox process, ridding your systems of toxins you we were exposed to over the day. In like manner, it is finishing the absorption process of nutrients you took in while you were awake, and is even producing such vital chemicals as melatonin, hormones, and human growth hormone, a vital element in the growth of children and injury healing in adults.
This continues until approximately 4 a.m., when your body begins to undergo the physical changes that prepare you for waking up, despite your obliviousness to this transition. Melatonin production decreases, you temperature and blood pressure increase, and breathing speeds up slightly. Your eyes open, you wake up, and the circadian rhythm repeats.
As stated previously, this cycle has evolved throughout the history of mankind, adapting to environmental demands. Along these lines, it’s interesting that while everyone’s circadian routine is approximately twenty-four hours long, the precise timing can vary slightly among individuals. For example, in the aforementioned example, 10 p.m. is the time sleep sets in. However, some people move in slightly earlier or later rotations. The result is the variance that we would use when referring to people as “morning larks” or “night owls.” Why such a discrepancy? Matthew Walker explains that our ancestors were wired to:
…co-sleep as families or even whole tribes…the benefits of such variation in sleep/wake timing preferences can be understood. The night owls…[would fall asleep] between one or two a.m.…the morning larks…would have retired at 9 p.m. and woken at 5 a.m. Consequently, the group as a whole is only collectively vulnerable…for just four hours rather than eight hours.[iii]
The scenario described earlier, to someone juggling many responsibilities, may seem like a pipe dream. In this day and age, such a schedule seems hardly obtainable considering our busy lifestyles. Yet, our cycles define how our bodies were meant to thrive. Have you ever wondered why people in our grandparents’ generation, many of them farmers, managed to stay so healthy into such late ages? If we examine their diets, we find a paradox. Their food was organic/farm raised (a positive contribution to their health!) but what they ate was often filled with fats and carbs—a diet doctors would steer today’s patients away from. Foods such as eggs, bread, gravy, and bacon were eaten regularly, while fresh fruits and vegetables may have only been available seasonally. However, due to the lack of television, the Internet, and other distractions, they often spent evenings in decreased activity, and when it was dark outside, the great majority went to sleep. When we scrutinize their lifestyles, we find that they lived in accordance with the ideal daily cycle. Each of the three themes of the circadian were honored: sleep (regulated by the sun’s rising and setting); nutrition (through the farming of safe and wholesome food); and activity (through manual labor and the habit of finding entertainment through activity and healthy social settings).
For some, it may seem that if we work against our own cycle long enough, it will eventually change. After all, those who fly to different regions of the world experience jet lag, but they soon recover. However, travel involves the fact that, in the new region, sunlight is operating on a different timeline—so, after a day or two, the body adapts. Working in a time zone where the body must operate against the sun has direr consequences. University of California in Berkeley’s professor of neuroscience, Dr. Matthew Walker, states:
Wakefulness and sleep are therefore under the control of the circadian rhythm, and not the other way around…[it] will march up and down every twenty-four hours irrespective of whether you have slept or not.[iv]
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This is particularly true for shift workers who must remain awake during nocturnal hours when their cycle wishes for sleep. These folks are regularly pushing against their body’s preferred cycle, and the manifestation of this physical taxation can have measurable disadvantages. A study in Occupational and Environmental Medicine found that employees who held such shifts “had lower scores on tests of memory, processing speed and overall brain power…[and experienced] cognitive deficits so steep that the study authors equated them to 6.5 years of age related decline.”[v]
Just like shift workers, the body’s organs and glands—such as the liver and the thyroid—do different jobs at different times of the day. In a production plant, an exact order of operations has to happen to produce a final product: If anyone is unable to properly carry out his or her responsibilities, the result is likely to be a defective product. For us, this means that timing is everything. For example, eating a bagel in the morning means that the liver has adequate time and prepared support to efficiently take in the calories, which will generally be burned throughout the day instead of becoming stored fat. However, eating the same bagel in the evening will result in the bagel being converted to stored fat. As we’ll explain a little later, what we eat isn’t all that matters where diet is concerned; it is also when we’re eating that’s significant.
Limiting our exposure to technology can add quality to our lives. While the sun is the greatest source of blue light, electronic screens produce a similar light in diminished capacity—not enough to supplement the lack of natural daylight—but adequate amounts to throw the body into wakefulness during the evening hours when the body should be preparing for sleep. You may think, “I can wind down with television just fine. I still get to sleep without trouble,” but unfortunately you may not be aware of the chemical alterations that your body should have gone through but didn’t, and thus aren’t privy to the declined quality of your sleep. Those who watch excessive television in the evening, stare at a computer too many hours late into the day, or even enjoy too much phone time during this segment of the cycle stunt melatonin development and harm their health by means of sleep deprivation.
On the other hand, lack of sunlight can tell the brain’s mechanism to falsely believe that it is dark outside, resulting in the generating of melatonin at sporadic times during the day. Often, our workplaces have limited natural light, which, coupled with sitting in a chair at a desk for too long, can trigger sleepiness. This often contributes to the need for additional coffee—a solution that, incidentally, doesn’t address the actual problem. The real issue in such a case is not the lack of caffeine, but is rather a deficiency of sunlight.
All this talk of sunlight may draw us to believe that circadian rhythm is a response system to our external world rather than a force from within. It would be simple to buy into the notion that when the sun comes up, we wake, and when it goes down, we sleep—just like clockwork. However, studies that began in the 1950s have shown that this timekeeper remains true, guiding human beings along a cycle roughly twenty-four hours and fifteen minutes in duration, even when we’re completely locked away from the influence of the sun, moon, and other cosmic markers of time. Further, although circadian rhythm is largely cued by blue light, other triggers influence (even throw off) its timing as well, including food intake, exercise, and blue light exposure at the wrong times of day. (We will talk about this more a little later.)
In the 1950s, a volunteer ventured far into a cave in the Andes mountains carrying only the simplest provisions: enough food to survive on for several weeks, some candles, and reading material. A rudimentary telephone was designed that could only call out to log the time to a volunteer. Each time the hiker felt sleep setting in, he’d report via telephone, and would do the same as he woke up. The experiment showed that his internal clock operated with near-perfect precision, with one exception: He woke up slightly later each day, and retired in the same fashion. In total, his cycle showed a pattern of being twenty-four hours and fifteen minutes long, but despite his clock being slightly longer than twenty-four hours, his rhythm was consistent for the duration of his cave-dwelling time. What was gleaned from these findings was that although adequate blue light or sunlight can trigger or sometimes even reset this internal timekeeper, it exists within our innate mechanisms, independent of our environment, and hardwired into our brains as a separate entity from the outside world. This proves that while our systems are able to adapt, we must follow the cycle for which we’re designed.
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[i] Walker, Matthew. Why We Sleep: Unlocking the Power of Sleep and Dreams. (New York: Scribner, 2017), Pg.14.
[ii] Ibid., Pg. 18.
[iii] Ibid., Pg. 22.
[iv] Ibid., Pg. 20.
[v] Oaklander, Mandy. “This Is Your Brain on 10 Years of Working the Night Shift.” Time Magazine Online. November 4, 2014. Accessed February 3, 2020. https://time.com/3556130/night-shift-brain-work-health/.