Sleep is a natural state that could not be controlled or forced. Our circadian rhythm, i.e. the body clock, is responsible for regulating our sleep-wake cycle which is roughly 24-hour per cycle. Governed by the rhythm, our alertness increases in the morning until around noon when we tend to experience a drop in alertness. This phenomenon is also called the “post-lunch dip”. Our alertness is gradually restored after the dip until it drops again at night time.
As we engage in various activities throughout the day, our body build up a sleep drive continuously. By night time, our sleep drive naturally approaches its peak. Furthermore, in response to darkness, our body secretes a hormone called melatonin which can increase sleepiness. With the two mechanisms of peaked sleep drive and increased melatonin level augmenting each other, we gradually fall asleep.
Disruption to the natural sleep-wake cycle can lead to sleep disturbances when human activities create a mismatch between our circadian rhythm and external environmental cues.
For example, exposure to light at night can disrupt melatonin secretion which is triggered by darkness. Using electronic devise at night with night switched off can have the same effect of suppressing melatonin secretion due to blue light emitted from screens.
It is because before the invention of these portable devices, sun light is supposed to be the major source of blue light in our natural environment. Therefore, our body clock can become confused by the contradictory co-existence of night time and exposure to blue light. Melatonin secretion is affected and as a result, sleep might be disturbed.
Shift work is another major cause of circadian misalignment because working at night requires us to stay alert when our circadian rhythm should normally dip. This is similar to jet lag experiences when we travel across time zones and the internal clock’s expected daytime and nighttime is reversed.
Just as darkness at night can trigger melatonin production, sun light is a factor that can enhance wakefulness and alertness. Therefore, in the case of shift work, workers are often recommended to wear sunglasses and shield from daylight as much as possible after work when they return home to catch up on the much needed sleep. On the contrary, exposure to sunlight can often help to ease jet lag by providing cues that help to shift our circadian rhythm to match the new pattern of alertness and restfulness.
Finally, stress and emotional issues can also disrupt our ability to fall asleep. Our body and mind are evolutionarily wired to stay in an aroused state so that we are well prepared for rapid reaction to threat when we feel stressed and disturbed. The state of alertness can make it particularly difficult to fall asleep. Consumption of caffeine and nicotine have a similar effect of increased alertness.
Sleep hygiene recommendations like using curtains or sleep mask, putting away electronic devices, practicing relaxation exercise, doing relaxing activities before bed time and limiting coffee or tea consumption from the afternoon all aim at minimizing disruption to our natural circadian rhythm.
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