Why Does Coffee Keep Me Awake?

by Peter Taylor | Last Updated: 17 January 2021

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Why Does Coffee Keep Me Awake?

Coffee is the most widely consumed psychoactive beverage in the world. American’s consumed nearly 26.5 million 60 kilogram bags of coffee between 2018 and 2019, and the figure is on the rise. People are passionate about their coffee, and its effects on sleep are an area of fierce debate, but first of all, why does coffee keep you awake?

Coffee keeps you awake due to its interaction with A1 receptors in your brain, which inhibit adenosine. Adenosine signals your body to become sleepy, and caffeine inhibits these signals by blocking their path to their receptors. This action causes feelings of alertness and reduction of tiredness.

Coffee affects the quality of your sleep in multiple ways. To understand how coffee affects your sleep, one needs to peek into caffeine’s physiological processes in the human body. If you ever wondered why you don’t feel alive until your morning Java, then read on.

Adenosine and Sleep

To understand how caffeine acts on your brain to keep you awake, you first have to understand the action of Adenosine triphosphate (ATP.) ATP is an energy-carrying molecule found in all living things, and it works by capturing energy from the digestive process and releases it to fuel other cellular processes.

ATP is responsible for energy transfer between cells, and once the ATP depletes, it breaks down into adenosine. Adenosine binds with a particular receptor in your brain called the A1 receptor. It fits into the receptor somewhat like a lock and key mechanism to create feelings of sleepiness and drowsiness.

At the same time, caffeine also blocks the A2A receptors, which increases the release of more dopamine. As you know, dopamine is the ‘feel-good’ chemical, so you don’t just get an alertness surge, but coffee can make you feel good.

As your waking day progresses, more and more adenosine is released, which is why you feel more tired as your day progresses. When your body runs out of readily digested sugars, adenosine signals your body to become sleepy so that we may rest and rebuild our energy reserves. The action of adenosine initiates REM sleep, which is an essential part of our sleep cycle.

Caffeine and Adenosine

Caffeine acts as an adenosine blocker by attaching itself to the same receptors to which adenosine naturally bonds. Caffeine binds to adenosine receptors in the central and peripheral nervous systems and organs such as the heart and blood vessels. Without the body’s natural adenosine signals for sleep, coffee drinkers experience a sense of wakefulness and alertness.

The urge to grab a coffee in the morning is fueled by a build-up of adenosine not entirely dissipated during the sleep process. The accumulation of adenosine is linked to the amount of coffee that you ingest. Drinking caffeine-rich beverages during the day creates build-up adenosine that can not be thoroughly flushed away in the sleep process.

Which makes you feel more tired in the morning, and you seek out more coffee. This cycle can be a repetitive routine in heavy coffee drinkers.

How Long Does Caffeine Last in Your System?

Once you ingest caffeine, it is quickly absorbed by your gastrointestinal tract into your circulatory system. Once you swallow your caffeine, it is absorbed rapidly into all body tissues and crosses the blood-brain barrier. The concentrations of caffeine usually peak in your body 30-60 minutes from ingestion, but this may vary between individuals from 15 minutes to 2 hours.

In medical terms, caffeine activity in your body is referred to as half-life, which reveals how long it takes for a concentrated substance such as caffeine to decrease to half its starting dose in the body.

Why Does Coffee Keep Me Awake?

Caffeine’s half-life in the human body ranges from 2 hours to 12 hours according to individual metabolism and absorption factors. Generally, it is accepted that the half-life of caffeine is roughly 6 hours. Even though the caffeine has reached half-life by the 6hr average, one needs to bear in mind that there is still coffee in your system.

If you are average weight and age and are not genetically sensitive if you take a dose of 200mg caffeine, it should break down by half in 5-6 hours. If you ingest 200mg of caffeine at 9 in the morning, you will still be left with 100 grams in your system between 2-3 in the afternoon. Add another strong cup in the afternoon and you are adding another 200grams to the existing 100grams so the effects may be cumulative.

A study published in the Journal of Clinical Sleep Medicine found that 400mg of caffeine taken 0, 3, and 6 hours before sleep all significantly disrupted sleep. Even at 6 hours, caffeine reduced sleep by an hour. This sleep loss over multiple nights would lead to significant effects on daytime function.

Can Coffee Keep You Up All Night?

In 2019 a media storm erupted due to a study published on the effects of caffeine on sleep patterns. Christine Spadola, Ph. D of Florida Atlantic University and her co-authors from Harvard Medical School published findings from a survey of 5,000 nights of collected data.

This data was collected regarding the effects of nicotine, alcohol, and caffeine on sleep when consumed 4-hours before sleep. They recorded no significant effects of caffeine.

After 850 media outlets jumped on the findings, Spadola herself was not in agreement with the media take on the study, saying that it is okay to drink coffee before bed. She herself mentioned that caffeine tolerance and individual sensitivities might have been behind the lack of caffeine effect findings.

Nevertheless, the results still proliferate on pro coffee sites using her collaborative study as the basis for their claims.

There is strong evidence to support the conclusion that caffeine ingested later in the day can cause poor sleep quality. Whether you will stay awake all night depends on caffeine consumed and factoring your genetics, age, enzymes, weight, and tolerance for caffeine.

If you drink a large amount of coffee before your regular sleep time, you can factor in the 6-hour average caffeine half-life, peak concentration times, and calculate to estimate how long coffee will keep you up all night.

How Does Coffee Disrupt Your Sleep Cycle?

Caffeine has been associated with disruptions in our circadian rhythms, creating a delay in our 24 hours based metabolic rhythm that keeps our bodies in sync with our world.

In a 49 day long study, researchers found that consuming the caffeine equivalent to a double espresso 3 hours before sleep-induced a ~40-min phase delay of the circadian melatonin rhythms.

Caffeine prolongs your sleep latency, which means that it takes you longer to fall asleep when you ingest caffeine. Caffeine can also affect your arousal frequency, which is how many times your brain wakes at night even if you don’t recall waking.

Caffeine can also reduce the length of slow-wave sleep. The effects of high caffeine doses before sleep have even been suggested to mimic insomnia in clinical trials.

Can Coffee Make You More Tired?

Because the half-life of coffee is quite lengthy, people who binge drink coffee might find themselves more tired than before. The adenosine builds up while your coffee concentrations are high and may even increase during heavy coffee bouts.

When you stop drinking coffee, your body gets affected by the high levels of adenosine and may cause irritability, drowsiness, and feelings of withdrawal.

The action of coffee restricts the blood flow into the brain, and when you stop drinking coffee, the blood flow increases, people who suddenly stop caffeine may experience bad headaches and the above effects. That is why it is advisable to reduce coffee intake over time instead of going cold turkey.

Why Does Coffee Affect People Differently?

Caffeine has varying effects on users due in part to their genetic makeup. Although these predispositions are not fully understood, studies suggest that genetic variations in adenosine receptors and main liver enzymes that metabolize caffeine are to blame.

Cytochrome P450 is responsible for metabolizing caffeine in the liver, and caffeine’s half-life is determined to a large extent by this enzyme.

Factors such as heightened tolerance to caffeine, medications, and age also have a part to play in how our bodies process caffeine. People who have caffeine sensitivity should be particularly careful about how much coffee they consume and the times that they drink coffee.

Coffee has a scientifically proven effect on your sleep behaviors, although these effects vary dramatically from person to person. If you feel that coffee is affecting your sleep negatively, you should experiment with your coffee consumption times. Begin by giving your body a 6-8 hour coffee cutoff before sleep and see if your sleep improves.


When it comes to our beloved brew, it is not all doom and gloom for coffee lovers. Coffee has been linked to long term memory enhancement as well as prevention of Alzheimer’s disease.

Not only that, but caffeine prevents colorectal and liver cancers and provides coffee drinkers with more antioxidants than fruit and vegetables combined. So don’t lose sleep over a little sleep disturbance.


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