Why do need sleep?

Being an IB student, the title of this article is pretty contradictory, seeing that I rarely get a full night's sleep. However, I've been feeling slightly lethargic and sluggish as a result of this poor habit. So, I've decided to carry out some research as to why humans are so dependent on such a simple, yet complex process.

So, why do we sleep?

To conserve energy

Firstly, sleep is essential for conserving energy. After a long and gruelling day, energy levels will inevitably droop. We need energy to carry out our basic needs; even breathing requires energy. An experiment done by Dworak et al. at Harvard Medical School found that ATP (adenosine triphosphate, or the energy currency) levels showed a surge in the initial hours of spontaneous sleep in wake-active but not in sleep-active brain regions of rats. Inducing sleep and delta activity (which is prominently observed during sleep) by adenosine infusion into the basal forebrain during the normally active dark period also increases ATP. Together, these observations suggest that the surge in ATP occurs when the neuronal activity is reduced, as occurs during sleep.

In deep sleep, blood flow is directed less toward your brain, which cools measurably. At the beginning of this stage, the pituitary gland releases a pulse of growth hormone that stimulates tissue growth and muscle repair. Researchers have also detected increased blood levels of substances that activate your immune system, raising the possibility that deep sleep helps prepare the body to defend itself against infection.

To restore cells

A theory, known as the restorative theory of sleep, was posited that sleep aids in repairing and repleting cellular components necessary for biological functions that become depleted throughout an awake day. This is backed by the findings many functions in the body such as muscle repair, tissue growth, protein synthesis, and release of many of the important hormones for growth occur primarily during sleep.

Typically, sleep is categorized into REM and non-REM. REM stands for rapid-eye movement, and the eyes dart back and forth without sending any visual information to the brain. This is also when most of the dreaming takes place. The brain goes through and sorts memories from the day. This period of rest allows the mind the chance to categorize these thoughts and potentially store them for later. Non-REM sleep is when the body gets in on the restoration action and includes short-wave sleep (SWS).

When we fall asleep, our production of growth hormone increases substantially. At the same time, necessary proteins are also produced by the brain, giving us the energy we will need to successfully take on the following day.

To control our emotions

Sufficient sleep, especially rapid eye movement (REM) sleep, facilitates the brain’s processing of emotional information. During sleep, the brain works to evaluate and remember thoughts and memories, and it appears that a lack of sleep is especially harmful to the consolidation of positive emotional content. This can influence mood and emotional reactivity and is tied to mental health disorders and their severity, including the risk of suicidal ideas or behaviours.

A very common mental health problem is linked to a lack of sleep: depression. Historically, sleeping problems were seen as a consequence of depression, but growing evidence suggests that poor sleep may induce or exacerbate depression. There is no clear cause-and-effect relationship, but rather a mutually enforcing one. This paves the way for new treatments of depression, as improving sleep quality may have a corollary benefit on reducing symptoms of depression.

To maintain a healthy weight

While there is some discord within the medical community about the exact nature of this relationship, the existing research leads to a positive relationship between good-quality sleep and moderate body weight. One common hypothesis about the connection between weight and sleep involves how sleep affects appetite, which neurotransmitters control. Neurotransmitters are chemical messages that allow neurons to communicate with each other. In this case, the central neurotransmitters are ghrelin and leptin. The former contributes to the feeling of hunger whereas the latter is responsible for the feeling of satiety.

A lack of sleep may affect the balance of these two neurotransmitters. In one study, men who got 4 hours of sleep had increased ghrelin and decreased leptin compared to those who got 10 hours of sleep. This dysregulation of ghrelin and leptin may lead to increased appetite and diminished feelings of fullness in sleep-deprived people.

Conclusion

While these four points are just several of the multitude of reasons why one sleeps, scientists have not been able to come up with a concrete conclusion as to why humans are so dependent on this biological process. Nonetheless, sleep is much more than just a restorative measure to conserve energy. It's a necessity, so that's why you should stop scrolling through TikTok during the witching hour!

Citations

Nunez and Lamoreux. "What is the Purpose of Sleep?". Healthline. Updated 20 June, 2023.

https://www.healthline.com/health/why-do-we-sleep

Legg, Timothy J. "What does it mean when we dream?". Medical News Today. Updated 13 October, 2023. https://www.medicalnewstoday.com/articles/284378

"Brain Basics: Understanding Sleep". National Institute of Neurological Disorders and Stroke. Updated 19 July, 2023. https://www.ninds.nih.gov/health-information/public-education/brain-basics/brain-basics-understanding-sleep

Dworak et al. "Sleep and Brain Energy Levels: ATP Changes during Sleep". The Journal of Neuroscience. 30 June, 2010. https://www.jneurosci.org/content/jneuro/30/26/9007.full.pdf

Harvard Medical School. "How sleep boosts your energy". Harvard Health Publishing. 21 July, 2020. https://www.health.harvard.edu/healthbeat/how-sleep-boosts-your-energy

Sunni et al. "Mental Health and Sleep". Sleep Foundation. Updated 16 November, 2023. https://www.sleepfoundation.org/mental-health