Why do we sleep?

When we talk about sleep, we tend to think of sleeping at night. Many animals also sleep at night. Have you ever thought that there is actually a certain law behind this common phenomenon, which is the content of the 2017 Nobel Prize - circadian rhythm.

Through a series of studies, researchers have found the molecular mechanism that controls circadian rhythms, which involves a series of biological molecules called "rhythmic genes" that form a complex regulatory network to regulate circadian rhythm phenomena.

However, perhaps what most touched everyone was a very simple reason – “go to sleep when you’re tired.”

Therefore, the significance of sleep is definitely not just the circadian rhythm, but it has actual health effects on the human body, namely: clearing metabolic waste and promoting body repair.

Let us introduce them one by one below.

01. The meaning of sleep: clearing metabolic waste

The human body is metabolizing all the time, and metabolic waste will continue to accumulate. Sleep will accelerate the removal of metabolic waste from the human body. This is one of the important meanings of sleep.

For example, there is a flowing fluid in the brain called cerebrospinal fluid, which can help remove metabolic waste and inflammation. When sleeping, the cerebrospinal fluid flow channels in the brain will expand by 60%, allowing the cerebrospinal fluid to better remove metabolic waste from the brain and promote brain recovery [1].

On the other hand, if you don’t sleep, metabolic waste will accumulate excessively in your body, causing serious damage to your body. For example, studies have shown that depriving fruit flies of sleep will cause the oxygen free radicals in their bodies to continue to accumulate, exceeding the body’s ability to clear them, and ultimately causing serious damage to the animals’ health [2].

In addition, the greater significance of sleep lies in the repair of the human body.

02. The second meaning of sleep: repairing the human body

Metabolic damage to the human body is unavoidable. Over time, these damages will become more and more serious, eventually leading to irreversible aging of the individual. Sleep is a process that can enhance repair.

For example, a typical example is DNA damage. The DNA in cells will be attacked by oxygen free radicals produced by metabolism, causing damage. Whether it is fruit flies, zebrafish, mice or humans, when they are awake, the level of DNA damage in the body will continue to increase, but when they sleep, the DNA damage in the body will decrease.

In order to understand the essence behind this phenomenon, researchers used zebrafish, a typical vertebrate model organism, as their research object to explore the secrets of what happens during its sleep process [3].

A series of studies have shown that when we sleep, DNA damage in the cerebral cortex is significantly reduced, and the reason behind this is that the body's DNA repair process is stimulated. Specifically, when our DNA damage continues to increase, the body will send a signal to let people fall asleep. At this time, the activity of DNA damage response proteins (DDR) Rad52 and Ku80 will increase during sleep, and then further promote the activation of the PARP1 pathway, start the repair of DNA damage, and allow the brain to recover. Conversely, if sleep is deprived, the activity of PARP1 will be inhibited, which will lead to the inhibition of chromosome and DNA repair during sleep.

That's why we need sleep, as it helps repair DNA damage that accumulates while we're awake, keeping us healthier.

So in the field of anti-aging, there has always been a very important saying: get your beauty sleep.

03. Why is it important to get a beauty sleep?

When it comes to skin repair, it is certainly not a simple surface repair to replenish what is lacking. Deeper damage such as daily metabolic damage is the root cause of skin aging, so it is particularly important to repair the root cause.

Root repair is also the focus of skin care research in recent years. The real repair must be to restore the collagen synthesis ability of cells at the cellular level, which requires deeper research. An important mechanism of many night-time repair skin care products is that they repair the cells at the cellular level. This is actually in line with our understanding that skin care may be more effective at night.

In short, sleep is not only a rhythmic need, but also a necessity for the removal of metabolic waste and repair of the body. Whether it is our skin or other parts of our body, they all need to rest and repair at night, so taking advantage of sleep to strengthen your repair will also make the effect better.

1 Xie L, Kang H, Xu Q, et al. Sleep drives metabolite clearance from the adult brain[J]. science, 2013, 342(6156): 373-377.

2 Alexandra Vaccaro et al., (2020), Sleep Loss Can Cause Death through Accumulation of Reactive Oxygen Species in the Gut, Cell,

3 David Zada, Yaniv Sela, Noa Matosevich, Adir Monsonego, Tali Lerer-Goldshtein, Yuval Nir, Lior Appelbaum. Parp1 promotes sleep, which enhances DNA repair in neurons. Molecular Cell, 2021

4. Maes, DH; Pernodet, NA; Slutsky, L.; Collins, DF; Goldgraben, K.; Pelle, E.; McCarthy, JT Method and Compositions for Treating Skin. US Patent 20090220481A1, 9 February 2009. ELC Management LLC.