Extract from Energise - 30 Days to Vitality. Chapter 6: The Circadian Rhythm and Chapter 7: Stress and Fatigue.

The daily sleep-wake cycle is by far the most obvious behavioural and neurophysiological manifestation of the suprachiasmatic nucleus’s activity and circadian rhythms. The suprachiasmatic nucleus is a tiny structure situated in the hypothalamus and makes up what is referred as the master clock.

Our body clocks are regulated by these 24-hour cycles. Darkness signals the body to lower temperature and to stimulate the secretion of melatonin, the 'sleep hormone’. Daylight can turn on or turn off genes that control the molecular structure of biological clocks, which also drives the release of cortisol. A rise in plasma cortisol is what wakes you up in the morning.
Circadian rhythms can exert an influence on hormone release, body temperature, blood pressure, immune, cardiovascular and renal function, cognitive performance and mood. They stimulate alertness and appetite, feeding behaviours, and digestion, and have important bodily functions intrinsically linked to the autonomic nervous system, a system that without our conscious effort controls breathing, heartbeat and digestive processes.
The sympathetic nervous system (SCN) is governed by a group of 'clock genes’, which gives rise to pronounced daily, monthly, and seasonal rhythms, although this tightly-regulated system can be influenced by sleep habits and lifestyle.
Daily morning exposure to sunlight positively affect circadian rhythms and the endocrine system. Spending the majority of your time indoors can thus destabilise the SCN’s activity and lead to hormone imbalances.

Disturbances in your circadian rhythms due to long-term sleep deprivation directly impact your state of health.
Deep sleep is a very important phase of mostly complete disengagement from the environment. It is associated with healing and repair of the body, and tissue growth. Human growth hormone is released during deep sleep.
Deep sleep has also been shown to strengthen the immune system, and sleep is necessary for the body to ‘rest and digest’, a phase orchestrated by the parasympathetic system.
The less your time spent in deep sleep, the less the body can repair. The removal of toxic waste and metabolic byproducts that have accumulated during the day may be compromised. The active process of the glymphatic system can be impacted and toxins can build up. Symptoms may start to appear. Difficulties focussing during daytime, poor cognitive abilities and behaviour changes, including irritability and depression, are some of the symptoms brought by regular lack of sleep.
I generally compare sleep to a garbage truck coming every single night to collect the waste products produced by the brain, cellular respiration and various other metabolic processes. If not removed, ‘garbage’ may pile up very quickly.
People suffering from chronic sleep loss are categorically missing out on the restorative effect of deep sleep. They may remain longer in REM sleep, during which time, blood pressure and heart rate greatly fluctuate but majorly remain elevated.

Stimulants and Fatigue

What is your first instinct when you feel concentration dropping and at the same time a dip in energy, but there is still so much more to do?

Do you reach for a chocolate cookie, a biscuit, a granola bar or a more ‘healthier' option, such as a date or protein-rich snack? Or do you prefer to drink a coffee and probably another one a bit later on? Or perhaps, a few cups of coffee and snacks together?

Many peer-reviewed papers have shown that several cups of coffee a day can be beneficial to health, particularly heart health; however, most studies do not clarify which type of coffee.
People are led to believe that their daily high-calorie latte fit into that category, or even their caffeine-containing energy drinks.

It is clear that we all must be objective about coffee, particularly those of us drinking many cups a day: relying on coffee to start the day, to pick up the pace after lunch, and keep up with demands in the afternoon.
The truth is that while caffeine gives an immediate boost in energy and performance, this is short-lived and you may feel more tired once caffeine levels in your blood are dropping. Daily consumption of coffee is actually shown to impact your energy over time — one way that makes caffeine truly addictive. You drink coffee to be more awake and yet you don’t realise that caffeine is the perpetrator, making you more tired each day, but also emotionally tired and irritable.

By blocking the ‘fatiguing’ effect of adenosine, caffeine acts as a stimulant. This is why you feel more alert, able to focus and be productive.

The way caffeine and other stimulants (e.g. nicotine, cocaine) negate the effect of adenosine lies in their molecular structure. Caffeine is similar in shape to adenosine and can lock onto adenosine receptor sites and prevent adenosine to bind to its receptors, making you more ‘awake’ and energised. As caffeine blocks the receptors, more and more adenosine is produced by the brain. Once caffeine wears off and cells are inundated by adenosine, you are instantly feeling more tired.

Most often than not this is happening chronically. By drinking (and relying) on ‘life-saving’ cups of coffee each day, you create imbalances in neurotransmitters in the brain.

The brain believes that there is not enough adenosine in circulation to counteract the overstimulating effect of other neurotransmitters, unaware that it is artificially driven by caffeine. On the long-term, you become tolerant to caffeine, but also ultra-responsive to adenosine. You may also experience the ‘caffeine jitters’ and lose concentration and focus.

You tend to drink more and more coffee (or highly-sweetened cow's milk or nut milk lattes) as the brain produces more and more adenosine, until you cannot operate without coffee at all. Forget about the benefits of caffeine studies talk about, because in such taxing conditions all you are experiencing is ‘caffeine fatigue’, which makes long-term withdrawal studies only capable of ambiguously revealing the net effects of caffeine.,
Your overall level of energy during the day may become chronically suboptimal: you may never really feel ‘100%’.

On the long-term, you feel tired and unable to concentrate and stabilise your mood, and possibly irritable. You may even feel worse if you attempt to cut down on caffeine. A condition known as ‘caffeine withdrawal’, in the same way any substance addict would feel. Because caffeine reduces the flow of blood to the brain, symptoms include headache, but also tiredness and fatigue, decreased energy and alertness, and difficulty concentrating.
Caffeine also influences dopamine and other neurotransmitters that are involved in feelings of calm and pleasure, and the reward mechanisms of the brain. This is another way that makes caffeine extremely addictive.