The Master Clock
Our internal “clock” regulates all activities that are happening inside of our bodies. But where is this clock? It turns out we have something called the MASTER CLOCK. This Master clock is situated in our brain, in the region called the hypothalamus. The scientific name for this Master clock is “suprachiasmatic nucleus” or SCN for short. It is a tiny region of the brain responsible for controlling circadian rhythms. The neuronal and hormonal activities it generates regulate many different body functions in a 24-hour cycle. Many aspects of mammalian behaviour and physiology show circadian rhythmicity, including sleep, physical activity, alertness, hormone levels, body temperature, immune function, and digestive activity. The SCN coordinates these rhythms across the entire body, and rhythmicity is lost if the SCN is destroyed.
The way that the SCN “knows what time it is” is by getting LIGHT or DARKNESS cues. Simply put, when it’s daytime outside, the eye, through the retina, gets light input. This light gets sent through the retinohypothalamic tract to the SCN. The SCN sends information to the pineal gland to modulate body temperature and the production of hormones such as cortisol and melatonin. If there is light, the body will start secreting cortisol (the wakefulness hormone), and when it’s dark, the body will begin secreting melatonin (the sleep hormone). When the SNC is entertained (synchronized) properly, these hormones will secret at the right time, ensuring circadian balance and health.
The optimal cycle would be cortisol secretion by day and melatonin secretion by night. However, as you might have expected, this not the case for most people. Constant exposure to artificial lighting (whether electrical light or light emitted from digital screens) disrupts this cycle greatly. Naturally, when the Sun starts setting down, we would be exposed to less and less light as the night progressed. Humans have lived both with light and darkness for millennia. Only in the last hundred years (even less in some regions) have we become accustomed to the comforts of constant lighting. We no longer have to endure dark evenings and pitch-black nights. But that luxury comes with a price. And that price is our health. Melatonin secretion is acutely suppressed by light exposure at night (1,2). When melatonin excretes during the day and cortisol during the night, we call it Chrono disruption. When melatonin levels are low during the night, one may experience light and restless sleep or the inability to fall asleep. On the other hand, when cortisol levels are low during the day, a person can get tired, fatigued and have a problem waking up.
It turns out that the melatonin-cortisol cycle is much more important to us than meer sleep-wake regulation. Numerous studies have declared melatonin as the body’s most potent antioxidant. In addition to boosting the production of the body’s army of protective, antioxidant enzymes (glutathione, superoxide dismutase and others), it regulates and maintains the health and balance of the mitochondria, which are the energy generators found in every cell. Healthy melatonin levels have been linked to healthy bones, breast health, brain health, heart health, joint health, better quality sleep, blood sugar support, weight loss, balanced hormone production, cognitive health and a healthier microbiome by supporting the proliferation of immune-supporting gut microbes (3–10). And all this is just a tiny bit of information about the importance of melatonin. The sunrise represents a shift in your circadian cycle. Melatonin levels plummet, cortisol and vitamin D levels rise, digestive enzymes are produced, and blood sugar levels rise to fuel the metabolic needs of the day (11).
Traditionally, people would wake up at sunrise or before it to do their hard day’s work before noon, before it got too hot outside. After intense labour, they would have a large lunch and rest. Later as the day was coming to an end, they would begin winding down and preparing to sleep. Rarely would people go to bed as late as we do nowadays. Maybe if there was some sort of celebration or a holiday. But for the most part, they were all in bed by 9 pm. And that is how our bodies evolved. Our clock is set that way. It is ingrained in us, this kind of timing.
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