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, caffeine is typically associated with coffee, however several foods and beverages contain it. 

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. He did so 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, it is in the brain and spinal cord where caffeine produces its well-known effects. 

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 energized 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 can 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 can apply 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 parameters measured 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?

In the US, the average amount of caffeine consumed is 135mg per adult per day. This roughly equates to 1.5 cups of coffee. The USFDA considers a daily intake of 400 mg a safe amount for healthy adults. Essentially, this equates to about 4 cups of coffee per day. However it is recommended that pregnant women should limit their intake to a maximum of 200mg per day and should check with their doctor to determine what is a safe level for their individual situation. 

Moreover, caffeine is not recommended for children under 12 years of age according to the American Academy of Pediatrics. In addition, for adolescents over 12 years of age, daily caffeine intake should not exceed 100 mg (equal to about one cup of coffee per day).(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 is shown to provide a more gentle energy boost without the jitters that typically accompany coffee intake. 

Related reading

• Vegan coffee cake recipe
• Lemon-infused matcha latte recipe

Caffeine and sleep

A hormone produced by our body called adenosine, plays an important role in deep sleep.In fact, it turns out that caffeine consumption can actually block the effects of adenosine. 

Caffeine binds to the adenosine receptors in our brain therefore lowering adenosine levels. It also affects the levels of other hormones involved in sleep such as dopamine, serotonin, GABA and norepinephrine. Moreover, melatonin can also decrease in the presence of caffeine given that both are metabolized by the liver. 

Furthermore, caffeine consumption later in the day or in the evening can affect sleep quality. However, it appears that regular caffeine consumers develop a tolerance to the substance. Consequently, this lowers their susceptibility to the negative effects of caffeine on sleep over time.

Therefore, if you are sensitive to the effects of caffeine, it may be a good idea to monitor the amount and timing of your intake, as mentioned previously regarding caffeine’s half-life. 

Caffeine, pregnancy and fertility

Much like caffeine can cross the blood brain barrier from the bloodstream into the brain and spinal cord, it can also cross the placenta in a mother’s womb. 

In fact, an expectant mother’s intake of caffeine directly passes onto the fetus. Moreover, if the mother’s intake is high, high caffeine blood levels will result in her fetus. Consequently, this reduces oxygen levels and blood flow, increasing the likelihood of miscarriage and low birth weight. 

For this reason, it is recommended that pregnant and breastfeeding women limit their caffeine intake to a maximum of 200 mg per day. Alternatively, some pregnant individuals choose to avoid caffeine altogether. 

It is recommended that in any case, pregnant and breastfeeding women discuss their caffeine intake with their doctor in order to determine what is most appropriate for them. 

Moreover, a review of the literature found that caffeine intake did not impact the risk of infertility, no matter the level of intake.(5)