Sleep and Caffeine - Risks and Benefits

Caffeine can combat sleepiness by increasing alertness and keeping you energized - at least, that’s what everybody knows.

Caitlin Goodwin, Nurse Practitioner
Fact checked by
Dr. Ifran Saddique
Medically reviewed by

Sleep and caffeine are two important factors for our health and well-being. Sleep is essential for restoring energy, regulating emotions, and boosting immunity. On the other hand, caffeine can combat sleepiness by increasing alertness and keeping you energized- at least, that’s what everybody knows.

But caffeine is a largely misunderstood drug, and it’s natural for it to affect us differently. For instance, while a cup of coffee may be helping you stay awake, heavy drinkers say it does not affect them. It’s not strange for some people to drink a cup of coffee before bedtime and sleep like a baby.

So what is caffeine, and how does it affect us? Is caffeine bad for you? Grab that cup of joe and read on for answers to these and other questions. 

What is Caffeine?

Caffeine is a natural Central Nervous System stimulant that belongs to the methylxanthine class. A bitter substance, caffeine is mainly used to stimulate the brain and help users stay alert. Caffeine is FDA-approved for use in headache and migraine medications. It’s also a common ingredient in most dietary supplements for weight loss. 

Common Sources of Caffeine 

Caffeine can be found naturally in various plants and can also be synthesized in laboratories. Common sources of caffeine include; 

  • Coffee- coffee is the most popular natural source of caffeine. There is roughly 60 mg of caffeine per teaspoon of ground coffee. 

  • Brewed tea- only teas from the camellia Sinensis species have caffeine. These include green tea, black tea, purple tea, white tea, oolong tea, and pu-erh tea. Herbal teas like chamomile, rooibos, peppermint, ginger tea, and hibiscus don’t contain caffeine. Decaffeinated teas are the way to go if you have caffeine sensitivity or prefer grabbing a cup of beverage before bed.

  • Cocoa- the USDA states that 100 grams of unsweetened cocoa powder contain roughly 230 milligrams of caffeine. Like in coffee, the caffeine content in cocoa will vary depending on the type of bean, roast style, and serving size. 

  • Chocolate (cacao) - an ounce of dark chocolate has around 12 milligrams of caffeine. Milk chocolate has 3.5 to 6 milligrams of caffeine. 

  • Kola nut- a common flavoring ingredient in most beverages, a kola nut consists of 2-3% caffeine by weight. 

  • Guarana- this plant’s seeds contain 3.6% to 5.8% of caffeine. Guarana has the highest caffeine concentration of all plants. For comparison, coffee beans contain 2% of caffeine by weight. 

  • Yerba Mate drink- this popular energy drink in South America contains 80-85 milligrams of caffeine per 8-ounce cup.  

  • Dietary supplements- there are no legal limitations on the amount of caffeine in dietary supplements. An analysis by the Agricultural Research Service found that most dietary supplements contain zero to 800 milligrams of caffeine

How Does Caffeine Affect Sleep? 

To understand caffeine effects on sleep, let’s first understand how it’s absorbed in the body. When you take a sip of your favorite caffeinated beverage, some caffeine enters your bloodstream through the mouth lining, throat, and esophagus. Almost 90% of the caffeine is absorbed through the stomach lining and small intestine.

When you ingest caffeinated foods and beverages, about 99% of caffeine enters your bloodstream in around 45 minutes. The effects of caffeine are noticeable within 10 minutes of consumption, while peak levels are achieved within 15 to 45 minutes.

The rate of metabolism varies between people, depending on factors, such as age, genes, medical conditions, and drug interactions. 

Caffeine is primarily metabolized in the liver by an enzyme called cytochrome. It has a half-life of 6 hours. That’s to say if you consume a cup of coffee with 100 mg of caffeine, around 50 mg will still be circulating in your system 6 hours later.

Another thing that most people don’t realize is that caffeine has a quarter-life of about 12 hours. To put this into context, a quarter of the caffeine you consume around noon will still be in your body at midnight. 

How caffeine works in the brain to affect sleep 

In the brain, caffeine passes through the Blood Brain Barrier to block adenosine receptors. Adenosine is a sleep-inducing compound that slows down neural activity, signaling the brain to sleep. 

Caffeine is a unique drug for two reasons. First, it’s able to mimic the structure and size of adenosine. Second, it party-crashes adenosine receptors without triggering them. Doing this blocks off the actual actors- adenosine- from latching onto the receptors. Thus, you stay awake and alert despite the high levels of adenosine in the body. But as caffeine levels fall over time, adenosine can reach and trigger the receptors, causing drowsiness. 

How does caffeine affect sleep?

A cup of Starbucks coffee may be all you need for that evening jolt. That’s good because it keeps you alert, thus boosting your productivity. But beware that caffeine affects the quality and quantity of your deep sleep long after taking the coffee. 

A study on the effects of taking caffeine before bedtime found that even caffeine taken six hours before going to bed had significant sleep effects. Another study found that consuming 200 mg of caffeine before bedtime reduced the amount of deep sleep by up to 20%.

A 20% deficit may not seem like a lot. But Prof. Mathew Walker says you’d need to age by 15 years to achieve such a significant reduction. 

Deep sleep is important because it’s when the body releases the growth hormone, also called somatotropin. The growth hormone is responsible for building, repairing, and restoring all body cells and body systems. 

Interrupted deep sleep means that you wake up feeling unrestored and unrefreshed. When this happens, the chances are you’ll innocently reach for another cup to wake up your brain in the morning. This ultimately becomes a vicious cycle, likely leading to caffeine tolerance. 

Even if you don’t have trouble falling asleep after drinking coffee, you’re not immune to the impacts of caffeine on deep sleep. While caffeine can boost alertness when you feel sleepy, it won’t fix the cumulative effects of chronic sleep loss. 

Considering caffeine’s effect on sleep and daytime functioning, how long before bed should you stop drinking coffee? Experts say 6 hours because that’s how long it takes the body to get rid of half of the caffeine content consumed.

How much caffeine is too much?

So if you’re planning to take control of your caffeine intake, how much is safe per day? Most sources agree that 400 mg of caffeine daily is safe for most healthy adults. That’s roughly the amount of caffeine in four 8-ounce cups of brewed coffee or 10 cans of Pepsi. 

Note that not all caffeinated drink makers indicate caffeine amount. The amount of caffeine indicated also may vary from the actual amount in the product. For instance, the 5-Hour Energy Decaf contains 6 mg of caffeine, regardless of its name. Likewise, Aspirin Bayer Select Maximum Strength packs 65 mg of caffeine per tablet. That’s why it’s vital to beware of hidden sources of caffeine, particularly if you have a caffeine sensitivity. 

How to Get Caffeine Out of Your System to Sleep 

Most coffee lovers ask, “can you flush out caffeine?” Unfortunately, there isn’t much that you can do once caffeine gets inside your system. The only way to get rid of caffeine is to let your body flush it naturally. However, there are a few things you can do to help the body and minimize the side effects of caffeine; 

  • Stop consuming caffeinated products when you experience adverse side effects of caffeine. 

  • If you can’t go without coffee, drink decaf coffee, so you enjoy the flavor without the jitteriness. 

  • Increase your water intake to avoid dehydration. Caffeine is a diuretic, and this makes its symptoms worse. 

  • Exercise regularly. A study shows that even moderate-intensity activities help cut caffeine half-life by half. 

  • Pay attention to foods, drinks, medications, and supplements that contain caffeine. 


How much caffeine is in coffee?

The caffeine content in coffee varies by type. An 8-ounce cup of brewed coffee has 70-140 mg of caffeine, while a shot of espresso packs around 63 mg of caffeine. A cup of instant coffee contains 30-90 mg of caffeine. 

Does green tea have caffeine?

Yes. An 8-ounce cup of green tea has 30-50 mg of caffeine. Though lower than caffeine in coffee, it’s still enough to boost your mood and brain function. 

Does matcha have caffeine?

Yes. A teaspoon of matcha tea contains roughly 70 mg of caffeine. Matcha is among the teas with the highest amounts of caffeine. 

How much caffeine is in coke?

The amount of caffeine in coca-cola depends on the drink. There are 32 mg of caffeine in a 12-ounce serving of coke. A similar serving of diet coke has a higher amount of caffeine at 42 mg. 

Verdict: Is Caffeine Bad for You?

Caffeine, whether in coffee, tea, energy drinks, or a bar of chocolate is not bad. Were it not for it, most of us wouldn’t have any identifiable personality. A nicely brewed cup of coffee brings order to our mornings, and is the start of great ideas. 

And don’t get us started on the benefits of caffeine, including improved heart health, weight loss, and prevention of Alzheimer’s and Parkinson's disease. 

Of course, caffeine has a few downsides- just like most drugs. But so long as you have your last cup six hours before bedtime, you can continue enjoying coffee without it disrupting your sleep.

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