28 Feb 2022
How long does caffeine stay in your system?
What is caffeine?
Caffeine is a bitter white powder less commonly known by its scientific name, 1,3,7 trimethylxanthine. In fact, scientists have studied the effects of caffeine for a long time, discovering the myriad of effects it can have on our bodies.
From increasing alertness and awareness to improving physical performance in athletes, caffeine is a powerful stimulant that can impact our physical and mental state.
Moreover, we typically associate caffeine with coffee, however it is found across several foods and beverages.
In addition, black and green tea, cocoa powder and kola nuts are all sources of caffeine. Cola drinks, energy drinks, chocolate and some non-prescription medications such as over the counter painkillers and cough syrups may also contain caffeine.
How caffeine affects our nervous system
Our body absorbs caffeine within approximately 45 minutes of consumption, and blood levels peak after between 15 minutes and 2 hours depending on the individual.
Moreover, a scientific term called “half-life” can be useful to understand the effects of caffeine on our body. Half-time refers to the amount it takes for us to eliminate 50% of the caffeine from our body. In fact, the amount of time can vary significantly based on individual factors. These include gender, age, body weight, liver health, medication intake and pregnancy status.
In the healthy adult population, the average half-life of caffeine is about 4 hours. However this can vary within a range of 2 to 8 hours. In addition, this may be useful to consider if you are sensitive to caffeine. In fact, you may want to time your caffeine intake so that you leave sufficient time between your last cup of coffee (or caffeinated food/beverage) and your bedtime.
The blood-brain barrier
An interesting characteristic of caffeine is that it enters the brain through what is known as the “blood-brain barrier”.
In fact, the blood-brain barrier, also referred to as the BBB, is a barrier between the brain’s blood vessels and the other parts of the brain tissue. It serves to protect the brain from any pathogens or toxins that circulate in our blood.
In the late 19th century, Paul Ehrlich, a German doctor, first discovered the BBB by injecting a dye into the bloodstream of a mouse. Consequently, the dye circulated through all of the body's tissues except for the spinal cord and the brain. This provided an initial insight into the separation between the brain and the bloodstream.
However, it wasn’t until the 1960’s that scientists accurately determined the existence of the BBB thanks to technological advances. In fact, they were able to identify a physical barrier through the lenses of highly specific microscopes.
Overall, caffeine’s ability to cross the BBB explains why it goes from our stomach to our bloodstream and ultimately to our central nervous system. In fact, caffeine produces its well-known effects in the brain and spinal cord.
Enhanced mental alertness?
Any regular coffee drinker will tell you that without caffeine they would probably struggle to be fully awake in the mornings! But what is it about caffeine that makes us feel more energised and alert?
Many people consume caffeine with the objective of increasing alertness. However, it appears from some research that caffeine does not boost mental performance above “normal” levels in those who regularly consume caffeine.
In fact, in regular coffee drinkers, caffeine withdrawal (i.e. overnight), reverses the effects of caffeine, lowering mood and alertness. Subsequently, consuming more caffeine reverses these withdrawal symptoms, however it may not do so above baseline levels.(1)
In other words, people can develop a “caffeine tolerance” if they regularly consume caffeine. Thus once they stop, withdrawal symptoms can kick in. In fact, symptoms include irritability, fatigue, headache and low mood.
Moreover, a study conducted on medium-high and non-low caffeine users observed the effects of caffeine consumption following overnight caffeine abstinence. Overall the researchers found that mental performance improved in medium-high consumers but not in non-low consumers.(2)
In fact, the only benefit in non-low consumers was decreased sleepiness. However this was offset by an increase in caffeine-induced anxiety and jitteriness.
Overall it seems that regular caffeine consumption leads to tolerance to its tendency to cause anxiety and jitteriness. However, tolerance to its effects on fatigue implies that regular consumption does not enhance mental performance.
And physical performance
People who seek enhanced physical performance commonly consume caffeine containing foods and beverages. This applies to regular people who exercise as well as professional athletes.
For instance, a review on the effects of caffeine in soccer players investigated the links between caffeine and physical performance, muscle damage and self-perceived levels of fatigue. The study showed that a moderate dose of caffeine consumed within an hour before soccer practice may enhance certain aspects of physical performance in players. However it did not impact muscle damage or perceived fatigue levels.(3)
Moreover, another study in elite female handball athletes investigated the effects of caffeine consumption on physical performance. The researchers measured parameters such as included ball-throwing speed, jump and sprint performance. Overall, caffeine consumption prior to exercise improved all measured parameters of physical performance amongst the athletes.(4)
Is caffeine bad for me?
According to EFSA, caffeine intakes of up to 400mg/day are considered safe for most healthy adults, with the exception of pregnant women. In the general healthy adult population, a single dose of caffeine of up to 200 mg does not raise any safety concerns. For reference, a cup of filter coffee (200ml) contains about 90 mg of caffeine.
Furthermore, for pregnant and lactating women, daily caffeine intakes of 200mg are considered safe and do not raise concerns for the developing foetus.(5)
However, despite safety levels, caffeine may affect sleep quality and quantity in some people. This is especially true if caffeine is consumed close to bedtime. Furthermore, in sensitive individuals, caffeine can increase levels of anxiety at doses above 400 mg per day. However, the exact dose may vary depending on the individual.
In fact, some people may even experience some anxiety after just one cup of coffee. If you suffer from anxiety or are prone to panic attacks, be aware that caffeine can speed up your heart rate and cause nervousness. These symptoms can sometimes feel similar to what is experienced during a panic attack.
Nonetheless, we are all different as human beings so it is normal that caffeine can have very different effects depending on the individual. If you are experiencing anxiety and think that it may worsen due to caffeine, perhaps you can try switching from coffee to matcha. Matcha tea can provide a more gentle energy boost without the jitters that typically accompany coffee intake.
