Adenosine and Sleep

Adenosine is an important chemical known as a nucleoside that exists naturally in all cells of the body. It is used to transfer energy within the cells by forming molecules like adenosine triphosphate (ATP) and adenosine diphosphate (ADP), and it is also one of the chemical messengers, or neurotransmitters, within the brain. In addition to various other functions, adenosine has been found to be an effective natural painkiller, widens blood vessels, and helps regulate heart rhythm.

Woman sleeping in bed
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How the Body Makes Adenosine

Adenosine is created naturally within the body from the combination adenine, a nitrogen-based substance, and ribose, a sugar. In addition to being a neurotransmitter, adenosine is classified as a chemical known as a xanthine. Every cell in the body contains some adenosine contained within DNA and RNA.

How Adenosine Impacts Sleep

Adenosine has an essential function in many biochemical processes and is one of many neurotransmitters and neuromodulators affecting the complex behavior of sleep, particularly the initiation of sleep. In the brain, it is an inhibitory neurotransmitter, meaning it acts as a central nervous system depressant and inhibits many processes associated with wakefulness. While awake levels of adenosine in the brain rise each hour and therefore is believed to be responsible for increasing levels of sleepiness that develop the longer a person stays awake.

During wakefulness, adenosine levels gradually increase in areas of the brain that are important for promoting arousal, especially the reticular activating system in the brainstem. With higher and higher concentrations, adenosine inhibits arousal and causes sleepiness. Then, adenosine levels decrease during sleep. Therefore, scientists have long extrapolated that high levels of adenosine in effect cause sleep. In fact, caffeine found in coffee, tea, and other caffeinated beverages, is a xanthine chemical like adenosine and works to inhibit sleep by blocking the action of adenosine within the brain, which increases wakefulness. In other words, when you drink caffeine, it achieves its stimulating effects by blocking your brain's adenosine processing. 

Stages of Sleep

While a person sleeps, his or her brain is still active during the various phases of sleep. The various stages of sleep all serve distinct purposes for rest and rejuvenation. In stage 1, heart rate and breath slow while the muscles relax and sometimes twitch. In stage 2 sleep, the body temperature drops while heart rate and breath slow even more. Eye movement stops during stage 2 sleep. Stage 3 is the deep sleep necessary to feel refreshed in the morning. In stage 3 sleep, your breath and heart rate are at their lowest levels, and you might be challenging to awaken. In REM sleep, the eyes move rapidly, and breath is fast and irregular. Heart rate and blood pressure are close to what they are when you're awake during REM sleep. We dream when we are in REM and the amount of time that we spend in REM decreases as we age.

The rate of adenosine metabolism seems to specifically impact or determine the quality of deep sleep, researchers have found, as well as a person's particular vulnerability to sleep deprivation.

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