How Does Coffee Keep You Awake?

Caffeine is the most used drug in the world, around 80% of adults consume caffeine on a regular basis (1). But most of us don’t consume caffeine by itself, rather we consume it in the form of coffee, soda, chocolate and energy drinks.

I, like most people, consume the majority of my caffeine from coffee, the black liquid gold that we all love and rely on to power us through our day. And I know I am not alone in this habit, coffee is the most drank beverage in the world. But how many of us actually know how it works? How does coffee make us alert for a couple hours, but soon wears off and sends us running for another cup? The answer lies in the an energy molecule called adenosine.

Last week, I wrote about why we fall asleep and how exercise impacts our need for sleep. (Click Here). Just in case you missed out on that post, here is a quick review. When we exercise we use an energy molecule called adenosine triphosphate (ATP). In order for movement and muscular contraction to occur the three phosphates get broken down and consumed for energy leaving just adenosine (ATP-> ADP->AMP-> A). Generally speaking, after this process occurs the adenosine crosses the blood brain barrier and accumulates in the brain. Adenosine is able to accumulate in the brain by attaching to its own specific receptors in the brain. Throughout the day this mechanism will occur over and over again. This accumulation of adenosine signals to the body that too much energy has been used and sleep is needed. This is known as sleep pressure and is one of the main reasons why we fall asleep at night.

But what is the relationship between caffeine and adenosine?

Well it turns out that your brain’s adenosine receptors struggle to tell the difference between adenosine and caffeine. Thus, when you guzzle down your morning coffee, caffeine hijacks the adenosine receptors. This hijacking causes a cascade of events in the body. Your heart rate elevates and your focus narrows. Instead of feeling sluggish from the adenosine, you now feel wired and ready to take on the day.

Not only does caffeine give you more energy by blocking the attachment of adenosine to its receptors, but it also triggers a mild fight or flight response in the brain. This response is triggered due to the increased neuron activity in the brain. When adenosine attaches to the brain it slows down the production of a neurotransmitter called dopamine, but when caffeine attaches the opposite occurs and the brain speeds up its production of dopamine and other excitatory neurotransmitters. This is one of the reasons why coffee makes us feel good. When dopamine is high in the brain we feel alert, curious and happier due to its effects on the pleasure centers of the brain. Unfortunately, this feeling can only last so long because your brain is quite clever. When caffeine hijacks the adenosine receptors, the brain begins to produce more receptors for adenosine to attach to. This increase in adenosine receptors allows the remaining adenosine molecules to accumulate in the brain and singal sleep. But that isn’t the only reason why you “crash” after coffee.

Caffeine has an average half life of about five hours (2), which means every five hours its effects become weaker and weaker. For example, if you consume 150 mg of caffeine at 6am, you will have 75 mg of caffeine in your system at 11am and then 37.5mg around 4pm and so on.

*But some people, like myself, are slow metabolizers of caffeine while others are fast metabolizers. Put simply, caffeine will stay attached to the adenosine receptors longer in the slow metabolizers versus the fast metabolizers. (Head to to find out) *

As this process occurs the caffeine begins to lose its control over the brain and adenosine takes over. And now since you have more receptors for adenosine you begin to feel even more tired than before. This increase in adenosine receptors and lack of caffeine in the brain leads to the dreaded “crash” that all coffee lovers go through at one time or another.  

Confused? Check out the video below:

Granted, everyone has a different definition of the “crash”. For some it is mild but for others it is traumatic. It sends them running for another cup of coffee and before the day is over they have consumed four to six cups. Overtime this dependence on caffeine can turn into an addiction and destroy your energy levels. A better way to increase your energy levels is through a quick 15 minute nap, meditation or exercise routine. This can be as simple as jumping jacks or a walk around the block. If you are stuck at the office and your boss isn’t a fan of jumping jacks then the supplements below can improve your focus and decrease brain fog. Nevertheless, I highly recommend taking a week off from caffeine or drinking decaf every three to four months to reset your adenosine receptors. And to all the coffee lovers, stay tuned for next week's post where I go over the benefits of the drink we love so much.  







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