Life on Earth has evolved to thrive with the natural cycles of the sunrise and sunset. Humans are no exception and are heavily influenced by this cycle. This cycle is known as our circadian rhythm; the daily rhythm we have to anticipate and adapt to the dramatically different conditions between day and night. The circadian rhythm is our body’s natural time keeping mechanism, also known as the biological clock. This clock controls our time-dependent biological processes. The most obvious process is sleep, but it also dictates our food intake, blood pressure, metabolism, and other things.
Obeying Our Body's Master Clock
Did you know there is a best time for you to eat, sleep, think, and even play sports? For each of us there is a perfect time to get up, be productive at work, have sex, or even exercise. We are ruled by time, whether that is an alarm clock, or our own internal clocks. Believe it or not, our bodies are full of many clocks. Such time-keeping is actually embedded in the DNA of our cells. Just as we have diurnal (activity, eating, being awake by day ) and nocturnal ( resting, fasting, sleeping) behaviors, so do our cells and systems. Signals are sent at the right times to keep our bodies working at their best. These mini clocks are regulated by a master clock in our brains. This master clock is known as the suprachiasmatic nuclei (SCN). This master clock keeps our bodies in tune with the 24 hour cycle of light and dark outside, ultimately synchronizing our cellular biology and behavior with the environment. It is important to note that everyday this “master clock” is reset.
The Circadian System By Day
By day, the circadian system shifts towards energy production and storage. Within the first hour of waking, cortisol levels greatly increase. This is known as the cortisol awakening response (CAR). After this morning peak, cortisol levels gradual decrease throughout the day. Cortisol levels remain low for the first half of sleep and then gradually rise during the second half. This cycle helps our bodies anticipate waking, ending a fast, and prepares us to feed and become active. Our cells are stimulated to begin processing nutrients and prepare energy reserves for our night time fasting period. Think of CAR as the jump start to get your day going and engines revving.
Melatonin & Circadian System At Night
Conversely, at night, the circadian timing system works to promote sleep and the breakdown of stored energy to maintain processes such as blood glucose levels. Akin to cortisol in the mornings, a hormone called melatonin is released by the pineal gland soon after sunset. Among other things, Melatonin helps to regulate sleep. Melatonin levels peak between 2 to 4am and gradually decrease after that. Through the SCN (the “master clock), melatonin production is enhanced by darkness and inhibited by light.
The Impact of Modern Technology
Our bodies are designed to follow the Earth’s 24-hour cycles, but they were not designed to deal with modern distractions. Cell phones, TV screens, LED lights, technology, and lifestyle demands, easily mess with these cycles. Such disruptions to our circadian cycle are not without consequence and have a negative impact on an array of biological processes in our bodies. These disturbances can easily effect our health, energy levels, and mood.
The Challenges of the Modern Work Schedule
Each of us has an optimal time to naturally wake up and go to bed so that our bodies can recuperate. When an alarm clock goes off it can be at odds with waking naturally. On the weekends, when we may not use an alarm clock, our bodies can get used to this 2-day change back to natural sleep patterns. So going back to work on Monday can feel like you are living in another time zone. Traveling in particular can really disturb our bodies. Our internal clocks fall out of line as we cross time zones and outdoor light conditions change.
If you are a nurse, law enforcement officer, working in mines, or in factory, be mindful of the impact your job may be having on your body. Jobs that are at odds with natural light conditions can be harmful. Shift workers in particular often have serious circadian misalignment and have an increased risk of metabolic syndrome, obesity, and diabetes. In addition, they are at a higher risk for developing cancer, gastrointestinal disorders, cardio metabolic disease, among other illnesses. (1)
Optimizing your Internal Clock
Avoid eating late if possible. The time of day that we eat also matters because our bodies handle foods during the 24 hour cycle differently. Eating late can disrupt the harmony between the master clock and other internal clocks, like the liver. Eat a meal at 9am and your body will burn the sugar throughout the day. Eat the same meal at 9pm and the sugar will likely be stored as fat as you sleep.
These circadian rhythms even play a factor in alcohol consumption. If you want a drink at the end of the day, liver enzymes will break down the alcohol faster than if you drank alcohol in the morning or with lunch.
Try and create habits that support your circadian rhythms to the best of your ability. Eat at regular times or earlier in the day. Go outside in the morning and get some sunlight. Work to optimize your sleep. Get enough sleep. Curtail your screen time at least an hour before bed. Switch to a book and work to calm your mind.