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Сircadian Rhythm Hormone: Sleep-Wake Cycle Disturbances Explained

Your sleep-wake cycle, or circadian rhythm, likes to keep a pretty strict schedule. Join Flo on its journey into the human brain to examine the hormones and complex mechanisms that dictate how much beauty rest you get each night.

The definition of circadian rhythm, as well as the term itself, has Latin roots and translates to “circa diem” or “about a day.” Every 24 hours, the body naturally syncs up with daylight and nightfall, determining how tired or alert you feel throughout the course of the day. 

This sleep-wake cycle instructs the brain to automatically rise with the sun and retire with the moon. When the circadian rhythm is somehow disrupted, it causes sleep-wake cycle disturbances like restlessness, insomnia, or fatigue. That’s why it’s crucial to practice healthy sleep habits to keep things running according to schedule.

An area of the brain called the hypothalamus manages the sleep-wake cycle. It’s an almond-sized region which connects the endocrine and nervous systems. The nervous system’s primary responsibility is to receive and respond to stimuli from sense organs like the eyes and ears. The endocrine system, on the other hand, controls bodily organs and tissues with the addition and subtraction of hormones. 

The sleep-wake cycle is also affected by the presence (or absence) of light. Since the circadian rhythm is synced with sunrise and sunset, natural light prompts a wave of activity throughout the body. 

To elaborate further, each morning, when your eyes detect sunlight, nerve cells tap into the body’s balancing systems and raise your heart rate and temperature. These cells are collectively referred to as the suprachiasmatic nucleus (SCN) and they reside in the hypothalamus. They’re linked to the optic nerve behind your eyes, which allows SCN cells to respond to ambient light. 

This phenomenon poses a major challenge for individuals who must work at night and sleep during the day. Unfortunately, even trying to sleep in on the weekends could throw the circadian rhythm out of balance, leading to grogginess and disorientation.

The SCN stimulates the production of melatonin, the main circadian rhythm hormone, at dusk and it delays the release of melatonin when dawn approaches. This dramatic shift in melatonin levels at night allows you to fall asleep and stay asleep. Inversely, the same circadian rhythm hormones help keep you alert during the day. 

According to the National Sleep Foundation, the majority of people feel drowsiest midway through the sleep cycle (between 2 and 4 a.m.), or when melatonin production is at its peak. There’s also a second bout of sleepiness right after lunchtime, roughly between 1 and 3 p.m. In fact, aside from humans, no other species sleeps just once a day. This essentially means that your body is biologically wired to crave an afternoon nap. 

As the sun sets in the evening, the SCN quickly senses the changes in light and prepares the body for rest. Melatonin levels rise, body temperature starts to drop, and organ function slows down.  

When twilight gives way to sunrise, the SCN jumps into action to boost alertness and productivity. As a matter of fact, experts believe that late morning is when you’re at your cognitive best. Then, after this sleep-wake cycle ends, a new one begins.

Whether you’re a night owl or a morning person, your body moves according to its own clock, and sleep-wake cycle disturbances are not uncommon. Despite being an unhealthy habit, people often attempt to fight their biological tendencies by working or studying late. Staying alert and focused the next day then becomes a huge struggle.

Since sleep-wake cycle disturbances take an obvious toll on mood, productivity, and your daily routine, it’s wise to keep that circadian rhythm on track. Luckily, there are a number of different ways to help adjust the sleep-wake cycle, including:

It lowers blood pressure and allows the body to slow down and prepare itself for a restful slumber. Reducing anxiety levels for both body and mind has a positive impact on overall health, making constant fatigue and unpleasant moods a thing of the past.  

Do you have trouble falling asleep at bedtime? Do you often wake up in the middle of the night? It’s extremely common for pregnant women to experience sleep-wake cycle disturbances. Everything from leg cramps to heartburn tends to aggravate pregnancy insomnia. When falling or staying asleep becomes a chore, consider purchasing a pregnancy pillow to support your body in new, and hopefully comfier, positions.

Another effective way to get better sleep is by creating a super-dark environment. Since the SCN easily senses ambient light, think about investing in a sleep mask or blackout curtains to enhance the body’s natural sleep responses.

On the other hand, if it’s actually become a bigger challenge to rise and shine in the morning, light therapy might be a good option. Natural sunlight triggers the circadian rhythm, and bright, artificial light (e.g., light boxes or therapy lamps) could inhibit melatonin production. Just be sure to discuss it with your doctor first, as prolonged exposure is potentially detrimental.

Lastly, it’s highly beneficial to create (and stick to!) a routine exercise program. Physical activity regulates all body systems, improves mood, and promotes better sleep.

If you’ve been struggling with sleep-wake cycle disturbances which are beginning to affect your daily routine, consult your doctor about how to address the issue. They may suggest taking melatonin supplements or another sleep aid to try and correct irregular sleep patterns.




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