"Body clock"

Our internal body clocks play a major role in our health. 

Our bodies move and rest in a cycle of roughly 24 hours. This is called the "circadian rhythm." 

The existence of the body clock was discovered about 50 years ago. The word "circadian" was coined at that time and is derived from the Latin words "circ" (approximately) and "dian" (day). It is also called "circadian" in literal translation. 

It is said that not only humans but also many other living things on Earth have a circadian rhythm that follows a roughly daily cycle. As life has evolved, been selected, and gone extinct for 3.5 billion years, only those organisms that could cycle through their internal activities in sync with the Earth's rotation have survived and survived to this day. 

Over the past 100 years, humanity has rapidly urbanized and our ability to travel long distances has increased to an unprecedented level. This means that modern life is full of things that mess with our biological clocks. Night shift work, working or studying all night, dining out, traveling or business trips overseas, watching live sports events overseas, and so on. Just because civilization has advanced, it is not likely that the circadian rhythms engraved in our DNA will change anytime soon. 

Going against our biological clock is, in a sense, going against our evolution as human beings! Living an irregular life that does not follow our biological clock is really bad for our health. Specifically, it is thought to lead to depression, allergies, obesity, diabetes, sleep disorders, and even cancer. And of course, it has a very negative effect on the beauty of our skin. 

Let's now explain the body clock, focusing on skin health. First of all, there is a "master clock" and a "slave clock" in the body clock. The "master clock" is located in the hypothalamus of the brain, and it controls the "slave clocks" in the cells throughout the body. 

This "child clock" is also built into the cells of the skin, and keeps a 24-hour rhythm in sync with the "master clock" in the brain. In other words, the skin does not simply cover the body; it also changes the way it functions on a daily cycle. 

First, during the day, the skin tries to act as a strong barrier against the body. To counter various stimuli such as ultraviolet rays (UV), it activates sebum production and thickens the skin. At the same time, it inhibits cell proliferation. This is because even if new cells are created during the day, they are easily destroyed by ultraviolet rays. It also raises the pH value to protect against bacteria encountered during outdoor activities. 

And at night, the skin activates its autophagy function to eliminate damage accumulated during the day. It also activates cell proliferation, which was suppressed during the day, and promotes the repair of DNA damaged during the day. Skin blood flow, amino acid content, and transepidermal water loss reach their peaks at night. Collagen production and epidermal loricrin and filaggrin expression also increase at night. 

The skin's "child clock" works to defend itself during the day and to focus on repair and strengthening at night. But what happens when this internal clock becomes out of sync with the actual time? For example, imagine you fly to Hawaii, which has a time difference, and go straight from the airport to the beach in a reversed day-night situation. Your internal clock thinks "it's the middle of the night" and focuses on amplifying your skin, so your defenses are weak and you're exposed to the full UV rays of Waikiki! Your unprotected skin will be severely damaged by sunburn, and the damage to the newly formed skin will slow down your recovery. 

As mentioned above, night is the time when the skin repairs and strengthens. That's why it's important for your skin to get a good night's sleep. The best amount of sleep is different for each person, and some people are short sleepers, but when it comes to skin, it's believed that adults need about seven hours of sleep. The time is just as important as the time itself. For the sake of the skin's "child clock," it's important to go to bed and wake up at the same time. This rhythm is very important (*). 

*Let’s leave aside for now the issue of whether you’re sleeping well or waking up at night. 

There is a point in maintaining the time you go to bed and wake up, and there is no need to stick to the time you fall asleep and wake up. As you age, the time it takes to fall asleep and wake up gets shorter. However, even if you go to bed at a fixed time, if you look at blue light from a smartphone or other device, your body clock will not consider you in bed! In other words, make it a rule for yourself to "stop looking at your smartphone at a fixed time at night" and "not look at your smartphone even if you wake up in the middle of the night." 

When you wake up, expose yourself to sunlight. Humans adjust their body clocks by exposing themselves to light (especially blue light) in the morning. If you don't do this adjustment in the morning, your body clock will be delayed by almost an hour in a day. This is why some people experience depression in the winter when dawn comes later and the weather gets worse. 

It is believed that being exposed to plenty of light in the morning and during the day increases the amount of melatonin secreted at night. Melatonin is an important hormone that affects the health of all tissues, but it is especially effective at making you feel sleepy at night. Light suppresses its secretion, so make sure you are in a well-lit area during the day and make your bedroom completely dark when you go to bed to ensure that melatonin is secreted all at once. Don't leave your smartphone or TV on, and close the blackout curtains to block out outside light. 

Try to eat meals at regular times as much as possible. In particular, it is very important to have breakfast at a fixed time. Also, avoid eating late-night snacks as they significantly disrupt your circadian rhythm. As with the Hawaiian trip mentioned above, research has shown that eating late-night snacks can cause your skin to lose track of time, which means your body's UV protection measures don't work properly the next day and you're more likely to get sunburned. 

As mentioned above, skin repairs itself at night and acts as a barrier during the day, but unfortunately these functions decline with age. This is a double whammy: skin is not repaired properly at night, damage accumulates, and the barrier strength during the day also decreases. 

To enhance the nighttime repair function even a little, wash your face thoroughly and apply a moisturizer or functional cream before going to bed. Even if you are young, the amount of moisture evaporating from the skin increases at night, making it more likely to dry out. Conversely, this is also the time of day when moisturizers and beauty ingredients are more likely to penetrate. It is better to apply a beauty cream that contains enzymes that repair DNA. And of course, during the day, be sure to apply sunscreen to prevent damage in the first place and minimize the damage that needs to be repaired at night.

AOHAL Evangelist Eriko Koyanagi