Following on from Caffeine, the widest used drug in the World? Post, it seems like the logical next step is to introduce you to the concept that caffeine stays into your system for much longer than you may imagine, and therefore potentially affect you sleep.
Most people realise that caffeine can reduce your ability to sleep, but what exactly does that mean? How caffeine increases alertness and reduces sleepiness is rather fascinating (well at least it is for me), at a chemical level caffeine enters the brain and binds to adenosine receptors. By doing this they block these adenosine receptors from being able to do their job, which is to bind to adenosine molecules.
Adenosine molecules are the by-product of muscle contractions and the breaking down of ATP to ADP and P molecules, which is the fundamental process that creates muscle contractions. These adenosine molecules build up over the day, due to the accumulation of movement and effort associated to the day. The more you do, the more adenosine builds up. This mechanism is commonly known as Sleep Pressure or Sleep Drive, and is one of two main drivers for our sleep-wake cycle, the other being your built-in time clock commonly referred to as your circadian rhythm.
By blocking adenosine molecules from binding to your adenosine receptors in your brain, you do not feel the build-up of adenosine as the process of it docking with the receptor is the key driver to the building of the building Sleep Drive.
The more caffeine you ingest, the more receptors are blocked, and the greater the build-up of adenosine which is waiting for receptors to become free. Almost like commuters waiting for a seat on a train.As the caffeine’s affects begin to wane, and the receptors become free, the adenosine that has built up latch onto the newly free receptors. If there is a large accumulation of adenosine, and many receptors become free in a short period of time, you will get a sudden tiredness overcome you. This is a flood of adenosine being appreciated by the brain and the full perception of yourSleep Drive will be felt.
How long does caffeine affect you in this way? I hear you ask. Depending on what you read, it can have a half life of between 4 and 6 hours, and a quarter-life of up to 12 hours. Doing the quick maths shows us that that 4pm coffee may be having a strong affect until 10pm to 4am, which can be an exceptionally large part of your nights sleep.
The major affects caffeine has on your nights sleep are increased latency, which means it takes you longer to fall asleep. It may often significantly affect the structure of your nights sleep, making the earlier part of the night more REM heavy when our bodies have created the optimal strategy of NREM dominated sleep during the first half of the night, followed by REM dominated sleep in the second half of the night. Having REM dominated sleep in the earlier part of the night also leaves you with a lower arousal threshold, which means you are easier to wake up as it is a lighter stage of sleep.
Hopefully this post gives you some insight into the physiological mechanisms of which caffeine works, and may put into perspective some of your experiences with regards to caffeine and your levels of tiredness.
Thanks for reading
Photo credit sleep.fm