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Coffee and sleep: How your morning cup affects your nighttime slumber

Caffeine consumption has increased in Australia over the years and sleep quality has suffered.

Written by
Rachael Crouch
Medically reviewed by
Last updated
April 19, 2024
min read
Coffee and sleep: How your morning cup affects your nighttime slumber
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Whether you're waking up with a latte from the café around the corner or knocking back instant coffee at home, over 75 per cent of Australian adults are enjoying one or more cups of that hot, bitter bean juice every day [1].

And by "enjoying", sometimes we really mean "relying on".

Caffeine consumption has increased significantly in Australia over the years, with more than one in four relying on at least one daily coffee just to get through their waking hours.

Anyone who has pulled an all-nighter before exams or gotten up far too early for that red-eye flight knows how helpful a stimulant coffee can be: caffeine increases alertness.

This is a well-known, highly popular and generally safe way to beat daytime sleepiness or to stay awake at night. It's the predominant reason we drink it, as caffeine lifts our energy levels and wakes us up for short bursts.

The good news is that the health benefits of coffee are becoming more and more apparent to science.

Dr Frank Hu, the chair of the Department of Nutrition at Harvard University's School of Public Health, said that moderate coffee consumption is healthy, not harmful, for people, and can certainly be incorporated into a balanced diet [2].

But, it's also well documented that caffeine and sleep are not good bedfellows. Caffeine affects our daytime functioning in that it can increase alertness and wakefulness, but it can also be harmful to nighttime sleep.

In this article, we are talking about caffeine consumption from coffee, not energy drinks. Energy drinks are loaded with chemicals and sugars that are detrimental to our health for a variety of reasons, and not just because of the caffeine levels included.

How much caffeine is in coffee?

A single eight-ounce cup of coffee contains between 95 to 200mg of caffeine, depending on how many shots of espresso, or teaspoons of instant, are in your mug.

In 2015, the European Food Safety Authority (EFSA) advised that caffeine intakes from all sources up to 400 mg per day, including single doses of 200mg of caffeine, are safe for adults in the general population [3].

But when we mean "safe", we mean that more than 400mg can cause headaches, heart palpitations, anxiety, light-headedness and "the jitters"; a jittery, edgy, unfocused feeling in your body.

This will not be the case for everyone, which means quantifying the right amount for sleep management can be tricky.

How does coffee affect sleep?

When you consume coffee, your stomach and small intestines absorb the caffeine very quickly. The maximum effects of caffeine usually occur between 30 to 60 minutes within consumption, although this timing is different for every person depending on your own unique biological makeup [4].

After being absorbed, caffeine crosses the blood-brain barrier: the extracellular fluid of the central nervous system where neurons reside. Inside the brain, caffeine blocks adenosine receptors. Adenosine is a sleep-promoting chemical produced in the brain during our waking hours [5].

Normally, adenosine builds up in the brain the longer you're awake. The more it builds up, the sleepier you become.

There is plenty of research that has been done on the effects of caffeine on sleep. Research has also shown that caffeine interferes with circadian melatonin rhythms, delaying the onset of sleep if consumed close to bedtime [6].

The buildup of adenosine contributes to your body's natural circadian cycle, telling us to sleep at night and be wakeful during the day.

Caffeine's interference with this process may explain its impact on circadian rhythm. Caffeine is considered an "adenosine receptor antagonist" — when caffeine blocks adenosine, we remain alert.

We also can't forget the cycle that caffeine consumption can cause.

You drink coffee in the morning to feel more awake, which can cause sleep disturbances at night and when you wake up feeling tired again, you often rely on caffeine to get through it.

Can you drink coffee and still fall asleep?

Before you start trying caffeine abstinence, rest assured that yes, you can drink coffee and still fall asleep. The onset of a deep, restorative, nocturnal sleep after coffee consumption completely depends on what time of the day you drink it.

If you drink coffee right before going to bed, it is possible to fall asleep although it will likely not be the optimal deep sleep needed for feeling well-rested the next day.

Caffeine can be the cause of sleep disruption, depending on a person’s sensitivity and how much they have consumed [7].

In one study, five people were given various treatments for 50 days: either a double-espresso caffeine dose, exposure to bright or dim light, or a placebo. The caffeine delayed their internal clock by 40 minutes, a shift about half as long as bright light, a stimulus known to robustly lengthen the circadian phase [8].

Caffeine can decrease the quantity of sleep as it delays the onset of REM sleep. That means you may not reach REM sleep at all, leaving you tired and fatigued the next day [9].

Another study found that consuming caffeine six hours before bedtime reduced total sleep time by one hour [10]. These effects also can be stronger in elderly adults as it takes their bodies longer to metabolise caffeine.

Caffeine will get you going during the day but could leave you tossing and turning at night – unless you're a "night owl" to begin with, a new study suggests [11].

In the study, early risers who drank coffee during the day appeared more likely than night owls to experience poor sleep quality. This is why the effects of caffeine intake appear to be different for every person.

While there are plenty of studies and empirical evidence-based trials showing how much caffeine will keep you alert and affect sleep, there are instances where sleep is not affected.

What we do know for certain is that excessive caffeine intake is not an alternative to sleep — no amount of caffeine will replace those much-needed ZZZZs you need every day to function, and even attempting to do so can lead to lots of health issues.

Tackling sleep disturbances head-on

Reducing your caffeine intake is a great first step to addressing difficulty sleeping. Try reducing the number of cups of coffee you have each day and enforce a rule that you can't have any more coffee after a certain time.

If you're still experiencing sleep disruptions, it might be time to look at an effective sleep treatment. Pilot's sleep support plan helps to regulate sleep, assisting you to fall asleep faster, improves sleep quality and allows you to wake up feeling refreshed and energised.

How much caffeine is too much?

Most adults can safely consume up to 400 mg of caffeine per day [9]. Caffeine intake that exceeds more than this can not only affect your sleep quality but also cause physical issues such as heart palpitations, sweating, jitters, anxiety and headaches.

For the average person, a cup or two of coffee shouldn’t impact your health or your sleep–provided you time it right. Approximately 200mg to 300mg, or two to four cups of coffee, is safe to consume.

While rare, a caffeine overdose occurs at around 15 mg/L. That's well over 10 cups to reach those levels.

Breathing trouble, agitation, confusion and even hallucinations can happen if you overdose on caffeine [12].

What to do if you can't sleep because of coffee

Sometimes we misjudge our caffeine consumption throughout a busy day, and we drink too much. Then, we toss, turn and lie awake in the middle of the night, willing sleep to come.

If you are lying awake after accidentally happens, there are some things you can do to help calm your body and relax your mind.

Practice meditation

The goal after consuming caffeine too close to bedtime is to make your body and mind feel as tranquil as possible.

One of the most effective ways to calm yourself is through the practice of mindfulness meditation, or focused, intentional thoughts to achieve a state of deep relaxation [13].

Take a bath

Studies have shown that warm baths (and even warm showers) can help you relax enough to fall asleep more easily [14].

Have a glass of warm milk

This isn't just for kids! Milk and other dairy products like cheese contain tryptophan, and tryptophan-enriched foods have been shown to improve sleep and mood [15].

Read a book

One of the worst things you can do for wakefulness is to lie there, staring at the ceiling or tossing and turning. Focusing on a book can relieve stress and induce tired eyes, allowing for relaxation to kick in and sleep to come on.

Turn off electronics

Another terrible thing for sleep deprivation is using your phone or looking at a screen right before bed. Your phone, tablet, reader or computer emits a short-wavelength enriched light, also known as blue light.

Fluorescent and LED lights also emit blue light, which has been shown to reduce or delay the natural production of melatonin in the evening and decrease feelings of sleepiness [16].

Blue light can also reduce the amount of time you spend in REM sleep, which is a vital stage of sleep for cognitive functioning.

Reduce your caffeine consumption

If you suspect your daily coffees are causing sleepless nights, you should think about lowering your intake until you figure out the right amount and at what times you should consume them.

Am I sensitive to caffeine?

You may have caffeine sensitivity if you're experiencing an intense adrenaline rush when you drink coffee. You might feel as if you've had five or six cups of espresso after drinking only a few sips of regular coffee.

Or, you may stay awake for hours at night even if you've only had one cup of coffee.

Symptoms of coffee sensitivity

You may be sensitive to caffeine if, after caffeine consumption, you regularly feel these physical sensations:

  • Headache
  • Insomnia
  • Nervousness
  • Irritability
  • Frequent urination or inability to control urination
  • Fast heartbeat
  • Muscle tremors

Caffeine sensitivity is different for everyone. Some people can have four or five cups of coffee in a day and manage their sleep quite well.

Other people can have heart palpitations from simply having green tea, which does have a small caffeine content.

Coffee and caffeine-free alternatives to try

If you're looking for a caffeine-free burst of energy to kickstart your day, pick you up over that 3pm slump or get through your daytime sleepiness, there are plenty of things you can reach for that aren't caffeinated drinks.

Get some sunlight

This may sound painfully simple, but it's true: going out into the morning sun for 10 minutes a day has marked benefits for people looking to become more energised [17].

Sunlight helps boost a chemical in your brain called serotonin which gives your brain energy and helps keep you calm, focused and positive. It also will increase your vitamin D intake, which provides the body with more energy over time.

Take a power nap

Napping will be difficult for people who work during the day. However, a daytime recovery sleep can improve memory, cognition and overall mood. A 30-minute nap will boost energy levels, too.

Speak to a sleep physician or your GP

If you are reaching for more than four cups of coffee a day due to excessive daytime sleepiness, you may be experiencing poorer sleep quality than you think.

This can be caused by sleep disorders like sleep-disordered breathing, obstructive sleep apnoea or bruxism [19]. Clinical sleep medicine may be useful here to help with sleep regulation, but not without consideration from a GP or sleep specialist.

Eat an apple or banana

Natural sugars are a much better source of energy than processed sugars (such as lollies, chocolate or sugary snacks).

An apple or banana's nutrients will release slowly as you digest, so your energised feeling lasts longer.

Eat a nutrient-rich diet

We know this is easier said than done, but if you want to stop reaching for a caffeinated beverage every day, a diet filled with whole grains and proteins offers slow-release energy, keeping you fuller and more energised for longer than the quick burst that coffee will give you.

Photo Credit: Clay Banks via Unsplash

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