Circadian rhythm is the 24 hour cycle biological processes that happen in your body, these cycles are controlled by various environmental ques like light and magnetic fields. The reason this is important is that every gene in your body has a clock gene in front of it that tells it what time it is and when to act, all of these clock genes are controlled by a master clock that is your SCN (suprachiasmatic nucleus).
Here is an example of a normal circadian rhythm:
Around 6am we will have a surge of cortisol to wake us up, this can change dependent on light levels and seasons. At this time Ghrelin should also be high (the hunger hormone) stimulating appetite, ghrelin has an inverse relationship with leptin which signals fullness and the receptors for both are found in the same areas of the brain.
6.45am we have a sharp rise in blood pressure and once light hits our retina the pituitary gland shuts off the production of melatonin.
At around 8.30am the gut is awakened and starts the process or moving yesterday’s food to the final stages of removal.
Around 9-10am we have the highest sex hormone levels that lead to our highest levels of alertness and stimulate us to go out and explore our environment.
Optimal muscular co-ordination comes in from 2.30pm with reaction speeds following an hour later.
At 5pm our cardio vascular system reaches optimal, this being the best time to do more intense workouts.
As the sun sets we see more changes that lead to the highest blood pressure of the day and an hour after sun set we see our body release leptin and IL-6 (interleukin 6) to signal the brain about our fat mass and inflammatory status.
For the next few hours leptin levels slowly rise as insulin and adiponectin levels fall. These fat hormone signals are what stimulates adenosine raise which leads to sleepiness.
This peaks around 10pm and the circadian clock SCN allows for melatonin secretion after around 4 hours of darkness, leptin levels will be high at this point and start to enter the brain.
By about 11.30pm the digestive tract is shut down for the night and the vagus nerve starts to power down.
As we hit midnight our body temperature starts to drop, by now melatonin levels should have risen enough to allow leptin to enter the hypothalamus. When this occurs our hypothalamus sends a signal down to our thyroid to allow UCP3 (Uncoupling protein 3) to burn excess fat as free heat.
3-4 hours after your last meal (also affected by light) you will see a surge of prolactin, this sets of growth hormone release which in turn stimulates autophagy (the recycling of cells). This all happens between the hours of 12am – 3am in a healthy human.