Stages Of Sleep And The Second Wind Phenomenon

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Even though there are a lot of factors which should be considered to achieve longevity, in my mind, there are only three principal factors which could affect an individual greatly in terms of living longer than anybody else:

• Diet
• Physical Activity
• Sleep

Of course, there are others such as genetics, environmental influences, accessibility to healthcare, gender and crime rates. The list goes on but in this article, I would like to talk about sleep; specifically about the importance of sleep in achieving longevity and why people were having problems with falling asleep if they were not having insomnia.

In a daily arousal-sleep cycle, the pattern of our sleep is controlled through a regulation of circadian genes which affect a few related structures in the brain, the most prominent one being the suprachiasmatic nucleus (SCN). The structures which have an influence on the pattern of our sleeping arrangement are called the circadian clock which is affected and synchronised with the solar clock.

What does it imply? It means, we have the capacity to be awake during the day and sleep during the night. This is the most prominent features of most living creatures. We demonstrated circadian rhythm, 24 hours oscillating patterns which are driven by a circadian clock.

Introduction

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Sleep is the natural periodic suspension of consciousness during which the powers of the body are restored

Definition By Merriam-Webster

Sleep has a healing property. It is needed for better memory, better physical and physiological function, better mood, muscle recovery etc. Generally, everyone knew it is important to sleep and all of the patterns were coordinated by the suprachiasmatic nucleus clock. As we age, the circadian clock ages with us which make sleeping disorder a common manifestation of ageing as a result of epigenetic changes, altering the circadian gene expression. There are two types of circadian clocks, which are:

• Central circadian clock (SCN)
• Peripheral circadian clock (liver, kidney etc.)

Interestingly enough, peripheral circadian clock works together with the central circadian clock which meant in ageing, metabolic failure could be one of the complications caused by peripheral circadian clocks. You might be getting an abnormal glucose metabolism which manifests as diabetes mellitus type II as a result of lack of sleep. Usually, some of the most common signs of changes in sleep pattern were presented as:

• Daytime sleepiness
• Reduced nighttime sleeping hours
• Sleep fragmentation

If you thought sleep doesn't influence how you process metabolic substrates such as glucose and lipid, you might want to rethink that. Blood sugar control, for example, is dependent on sleep quality which is usually measured by duration and quality. People who have trouble sleeping would have a higher risk to be diagnosed with diabetes type II. If you have been deprived of sleep before, you would notice an inappropriate feeling of hunger. This is due to the fact that sleep is crucial for regulating a few hormones which are related to satiation such as Leptin and Ghrelin. Leptin is a satiety hormone while Ghrelin is a hunger hormone. A proper sleep modulation would regulate leptin and ghrelin at an appropriate level.

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However sophisticated sleep is, sleep quality and duration are multifactorial. There are many factors which can affect how you sleep during the night. People who were having depression might be an insomniac or a hypersomniac. People who have bipolar disorder might be needing less sleep than usual when he/she is in a manic state. Some studies conducted recently have found that people who were working out in the morning were found to have less problem with sleeping at night. Sleep and longevity are not as simple as people used to think. Too little or too much sleeping could put yourself in jeopardy. There is an increased chance of getting various kind of diseases which are fatal if sleep was chronically irregular.

Sleep Stages and Cycles

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There are 5 sleep stages and every an hour and a half to two hours, the sleep cycle will complete all five sleep stages and repeat itself. It is a cyclical representation of sleep patterns which comprise of multiple emission of brain waves. Sleep stages can be divided into two which are:

• Non-REM sleep stages
• A REM sleep stage

*REM stands for rapid eye movement.

• Non-REM sleep stage(Stage I): This is a phase which allows you to be woken up easily (by noise for example). Your sleep was superficial and your sleeping wave patterns were starting to take hold. It is quite difficult to identify what kind of brain wave activity which predominant at this stage since it's better characterised by a mixed waves pattern. People might be feeling a sense of falling which usually followed by intense muscle contraction. People usually start their sleep cycle with stage one except for a newborn and people who have been suffering from narcolepsy.

• Non-REM sleep stage(Stage 2): This is a more stable version of sleep stage compared to the first stage of a non-REM sleep cycle. I mean, if you want to wake someone who has submerged into the second stage of the sleep cycle, you might need a little bit more than making a noise; they would require much more intense stimuli to regain their consciousness. This stage of sleep cycle was particularly important for memory consolidation which is represented by a marked increase in sleep spindles which is a crucial component of the process. Sleep spindles is a marked increase in brain waves activity which observed in the thalamus.

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• Non-REM sleep stage(Stage 3 and 4): Delta waves is the hallmark of the third and fourth stages of the sleep cycle. In the third stage of the sleep cycle, the appearances of delta waves were mixed with the other waves which can be found in the first and second stages of sleep. This is the stage where people might be having a nightmare, talking inappropriately during sleep and in children; bedwetting. Both of stage 3 and 4 of the sleep cycle have been termed as the slow-wave sleep cycles which are characterised by the appearance of slow delta waves. Stage 4 of the sleep cycle comprises almost exclusively of the slow wave activity which holds the highest arousal threshold.

• REM stage of the sleep stage: This is a stage which is represented intensely by a mixed slow and fast brain waves activity. Alpha waves, delta waves, sawtooth waves; you named it. The hallmarks of REM sleep were reduced muscle tone, rapid eyes movement from side to side and hectic brain waves activity. It is safe to say that, reduced muscle tone was a justified physiological event which restricts us from acting out our dream. In a study conducted by Crick and Mitchison in 1983 which has been published entitled "The function of dream sleep", they emphasised the importance of REM sleep for memory consolidation. Stage 2 of the sleep cycle might not be working alone after all.

The pattern of the sleep cycle is not simple. It would not progress from stage 1 to 4 and then enter REM stage before it will repeat over and over again in a cyclical pattern. The sleep cycle is composed of 3 type of sleep:

• Light sleep (stage 1 and 2)
• Deep sleep (stage 3 and 4)
• REM sleep

The order would be from light to deep and then back to light again before it enters the REM cycle.

An example of sleep cycle would be:

Stage 1 (light sleep) – Stage 2 (light sleep) – Stage 3 and 4 (deep sleep) – Stage 2 (light sleep) – Stage 1 (light sleep) – REM Sleep

Example Taken From Tuck Website

When the sleep phase has completed REM cycle, the sleep cycle complete. It will repeat itself, again and again, only the thing is, the deep sleep stage duration in a sleep cycle would reduce as the sleep duration increases. Every cycle would take about an hour and a half to two hours to complete and for every sleep, an individual will experience 5 sleep cycles.

The Second Wind Phenomenon

Timing is important. While it was assumed, achieving longevity by sleeping adequately is an effortless technique, without paying attention to the time in which we ought to sleep could cost us later. We knew that sleep patterns were determined by circadian rhythms which are controlled by various organ chiefly the suprachiasmatic nucleus (SCN). Apart from SCN, the pineal gland is another organ which is crucial in regulating sleep patterns based on the solar clock information obtained from the optic nerves of the eyes. Light changes will trigger this particular organ to secrete a hormone which is required for sleep. This hormone is called melatonin.

Secretion of melatonin is light dependent. Melatonin is secreted when the amount of light in the surrounding reduced but when there is a lot of light, the amount of melatonin produced is negligible. This is one of the organs which regulates our sleep behaviour so that we sleep at night and not during the day. The secretion of melatonin, however, would decline as the hour increases. It is at its peak level in between 10 pm to 2 am and started to decline afterwards. The role of melatonin in regulating sleep cycle is important and the consequence in the absence of it can be observed in the elderly. Ageing process caused a whole lot of complications and one of them being reduced production of melatonin.

Melatonin is an interesting hormone. Due to its antioxidant property, it plays an important role in preventing cellular damage caused by reactive oxygen species and other kinds of oxidant which are responsible for causing diseases. You must have heard the phrases "the most important item in your makeup bag is a good night sleep". It's literally is. Reduced amount of oxidants in the body correlate to a slower ageing process which would lead to longevity. People who sleep adequately also might appear younger than people of their age.

So what about the second wind phenomenon? Based on the information about the secretion of melatonin, we can say that the most beneficial, regenerative and crucial sleep time would be between 10 pm to 2 am as this is the time which is correlated with a higher than average secretion of melatonin compared with the other time. As melatonin is a hormone which induces sleep, generally, more hormone would mean, the time spent in the deep stage of the sleep cycle would increase. After 2 am, as the hormones decline, the sleep will become more superficial.

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In the second wind phenomenon, if you stay awake past 10 pm, it will be more difficult to fall asleep which can lead to fatigue when waking up in the morning. Let me put it this way, if someone stays awake past 10 pm, they were usually in a bright room which interferes with the formation of melatonin. Exposure to a computer screen, handphone and any electronic devices which emit light would make it worse. As the information collected by pineal gland came from the optic nerves of the eyes, this would not allow a normal secretion of melatonin which hindered the process of cleaning up free radicals. The few melatonins left would be used for making us sleep rather than serve the metabolic need of cleaning up free radicals.

You will realise that falling asleep would be difficult past 10 pm and after a certain period of time, you will experience a surge or a period of hyperactivity which cannot be explained despite feeling tired from the daily activity. It is important for us to know how and when to take advantage of the natural brainwave triggered by melatonin to optimise health and longevity. Melatonin is one of the most powerful antioxidants which is only secreted at night. Changing your sleep timing would exert an enormous effect towards your overall health.

Sources

• Klein, L., Gao, T., Barzilai, N., & Milman, S. (2017). Association between Sleep Patterns and Health in Families with Exceptional Longevity. Frontiers in Medicine, 4, 214.
• Institute of Medicine (US) Committee on Sleep Medicine and Research; Colten HR, Altevogt BM, editors. Sleep Disorders and Sleep Deprivation: An Unmet Public Health Problem. Washington (DC): National Academies Press (US); 2006. 2, Sleep Physiology.
• Sleep and Longevity
• Stages of Sleep and Sleep Cycles
• Circadian clock