The Science Behind Sleep
The Circadian Rhythm
The circadian rhythm is our body clock. It regulates our sleepiness and our wakefulness. Melatonin which is made by the pineal gland in the brain helps to control this. It is our sleep hormone.
Natural light influences how much melatonin is produced by the gland. In the dark melatonin is produced, and in daylight, production stops. Melatonin production typically occurs at about 9 pm, and your blood levels stay raised for about 12 hours. Once melatonin levels rise in your blood, you become less alert. Then the sleepy feeling tends to occur unless environmental factors such as bright lights and stimulants inhibit it.
Bright lights including indoor lighting can directly inhibit the release of melatonin. Daylight also triggers the release of stimulating hormones such as cortisol, which helps to wake you up.
The Sleep Cycle
Sleep is a cyclical state composed of stages which vary throughout the night. Each sleep cycle lasts about 90 to 120 minutes, which repeats throughout your length of sleep. An adult will on average experience 4-6 sleep cycles a night.
The three core types of sleep are light sleep, deep sleep, and REM (dreaming) sleep.
Deeper sleep occurs in the first half of the night, and lighter sleep during the rest. Your first sleep cycle is usually made up mostly of deep sleep. This initial stage is a crucial part of sleep and is when most of the restorative processes occur.
The Stages of Sleep
There are five stages of sleep. Stages one and two are light sleep, three and four consists of deep sleep, and five is called the REM (Rapid Eye Movement) or dreaming phase. We enter early sleep, Stage 1 when our melatonin levels have risen.
Stage 1 usually lasts a few minutes. Stage 2 makes up a bulk of our night's sleep, around 50%. During deep sleep (Stages 3 and 4) our body and mind repair and rebalance. It is during this time that our stress hormones reduce, our energy stores are replenished, our muscles and tissues heal, growth hormone is produced, detoxification occurs, and our emotions are processed.
A large proportion of healing occurs during the first part of our deep sleep early in the night. Ideally, this first phase of sleep should occur before midnight as it is a vital component that can affect the quality of sleep. By working late into the night, or using electronic devices before bed, it sets back this essential process occurring.
Stage 5 (REM) sleep is the shortest during the first cycle of sleep, lasting typically under 10 minutes, and lengthens through your sleep to approximately 45 minutes in the early hours. It is also an important part of your sleep and is when your brain is extremely active. It is during this stage that the parts of our brains involved in learning are stimulated. It helps to process the information we have gathered throughout the day.
The more you stimulate your mind just before sleep, the more REM sleep will be required to sort out this information, and the less deep and restful sleep will be attained. This can leave you feeling overtired in the morning as if you have been overworked all night with all that excess mental energy.
The pattern of these stages will differ from night to night and person to person. It is also age dependent, for example, sleep often becomes lighter with age.