Caffeine’s Effect on Sleep: How Long Does It Last?

Mary Sweeney - Updated on July 12th, 2023

If you can’t start your day without a nice, strong cup of joe, you’re not alone. Did you know that coffee accounts for approximately 50% of the world’s caffeine intake? Sounds like a pretty popular drink! However, coffee isn’t the only thing that contains caffeine. This powerful substance is found in things like tea, sodas, and even your favorite chocolate bar. Caffeine wakes you up, gives you energy, and prevents that awful headache that you’ll get if you don’t have it. But did you know that caffeine can have negative effects on your sleep?

What is Caffeine?

Caffeine is a naturally occurring stimulant found in tea, cacao, and coffee plants. It can be found in the following:

  • Coffee
  • Tea
  • Some energy drinks
  • Chocolate
  • Soda
  • Some over-the-counter migraine medications

Caffeine levels will vary in different items. To give you an idea of caffeine content in different items, check out the examples below (source):

  • Espresso: 240–720 mg
  • Coffee: 102–200 mg
  • Yerba mate: 65–130 mg
  • Energy drinks: 50–160 mg
  • Brewed tea: 40–120 mg
  • Soft drinks: 20–40 mg
  • Decaffeinated coffee: 3–12 mg
  • Cocoa beverage: 2–7 mg
  • Chocolate milk: 2–7 mg

How Does Caffeine Work?

Caffeine has a stimulating effect on the body, meaning it increases the activity coming from the central nervous system. After it has been consumed, caffeine is absorbed from the stomach into the bloodstream, eventually being broken down in your liver. It travels to your brain and other parts of your body and can cause many different effects, including:

  • Increased heart rate
  • Feeling more alert or awake
  • Regular or more frequent bowel movements

So how does caffeine make you stay more awake? Good question – and the answer may surprise you. Your body produces a neurotransmitter called adenosine. Its job is to eventually make you feel tired so that you rest when you need to. Throughout the day, adenosine levels build up in your body, making you feel tired towards the end of the day. Caffeine works to block the effects of adenosine in the brain, making you feel more awake and alert. In addition, caffeine can also stimulate the increased production of other neurotransmitters like adrenaline and norepinephrine, leading to more alertness and awareness.

Negative Effects of Caffeine

Caffeine may sound too good to be true - a substance that gives you energy and increases alertness. But there are a few negative effects of caffeine. They include:

  • Palpitations
  • Racing heart
  • Headache
  • Jitters
  • A “crash” in energy levels

Positive Effects of Caffeine

Several thousand studies have shown the positive effects of caffeine on health. Such effects include a decreased risk of developing:

  • Alzheimer’s disease
  • Parkinson’s disease
  • Colon cancer
  • Gallstones
  • Cirrhosis

Caffeine has also been shown to prevent asthma, boost your mood, and even possibly prevent cavities. Just remember, all caffeine intake in moderation!

The Sleep Cycle

In order to understand the effects of caffeine on sleep, let’s do a quick overview of the human sleep cycle. Sleep is a vital process that keeps our bodies functioning at optimal levels. A sleep cycle normally lasts about 90 minutes and can be broken down into two different types: Rapid eye movement (REM) sleep and non-REM (NREM) sleep. Within those two different types, there are 4 stages of sleep:

Stage 1: Stage 1 of NREM sleep is light sleep, lasting only a few minutes or so. Here, your body is preparing to fall into a deeper sleep, your eye movements slow down, and you begin to relax. During this stage, you can be easily awakened since you’re only lightly sleeping.

Stage 2: During this stage, you’re still lightly sleeping but your heart rate slows down, your muscles relax significantly, and your body temperature decreases slightly. Eye movements will slow down during this stage, and your brain waves slow down with occasional spikes in activity – you’re falling more deeply into sleep.

Stage 3: This NREM stage is restorative sleep, the kind that makes you feel refreshed. If someone were to wake you up during this stage, you would likely feel disoriented for a few minutes before recognizing your surroundings. Our eye movements slow down or stop, and it’s very difficult to wake us up. This stage is an important one – it’s where your body starts repairing muscle, strengthening your immune system, and other vital processes.

Stage 4: Rapid eye movement (REM) sleep. During REM sleep, our eye movements speed up dramatically, as the name suggests. REM sleep is the stage where you dream the most, and it’s thought that the eye movements are related to the dreaming that you’re doing. During this stage, most of your muscles are in a paralyzed state, to keep you from acting out your dreams. REM sleep gives your brain the energy it needs to keep you alert during the day, which makes it an ultra-important component of the sleep cycle.

While the average sleep cycle lasts 90 minutes, you will go through several cycles of varying lengths over the course of a night. During your first few sleep cycles, you’ll go through long cycles of NREM sleep, followed by a few cycles of REM sleep. Research also shows that the time of day can affect what type of sleep you get. For example, it is thought that most NREM sleep happens between the hours of 11 pm and 3 am, and REM sleep more often happens between 3 am and 7 am (source).

Caffeine and Sleep

If caffeine increases alertness and makes you feel less tired, it makes sense that it can affect your sleep if not consumed in moderation. Caffeine has a half-life of six hours, which means that six hours after consuming a substance containing caffeine, half the amount of caffeine will remain in your system. For example, let’s say you drink an eight-ounce cup of coffee containing 200 mg of caffeine at 6 pm. At midnight, 100 mg of caffeine will still be present in your body and affect different organ systems, potentially disrupting your potential for a good night’s sleep. While you may be able to fall into those initial one or two stages of sleep, chances are high that you won’t be able to fall into the deeper stages of NREM and REM sleep. 

The second effect caffeine can have on sleep is on your adenosine levels. Adenosine levels cause your brain to feel tired and are part of the reason you’re ready for bed at the end of the day. Caffeine binds to adenosine receptors in your body and blocks them, decreasing the amount in your body and therefore increasing your alertness. This, in turn, negatively impacts your ability to get quality sleep, including the deep REM sleep we so desperately need.

The effects of caffeine on your sleep will take a toll eventually and will turn into a vicious cycle. If you’re not getting quality sleep because you have had too much caffeine, you will likely wake up in the morning and not feel refreshed or alert. Fatigue and lack of alertness will prompt you to reach for a cup of coffee, with several cups throughout the day. You’ll need caffeine later in the day to make it through, and the half-life of caffeine will cause you to get less than optimal quality sleep.

Tips for Caffeine Intake

The caffeine-sleep cycle can be broken – here are some helpful tips to consider when consuming anything that contains caffeine:

Consider the time of day. Earlier, we discussed the half-life of caffeine. If you find yourself reaching for something containing caffeine later in the day, remember that half of the caffeine you’re consuming will still affect you six hours after you consume it. If you have an early day and need to be focused, cut back on your caffeine intake the day before.

Hydrate. Beverages containing caffeine have a diuretic effect on the body, meaning they will have you running to the bathroom more frequently. If you’re not replacing the fluid you’re losing, you’ll become dehydrated. Dehydration has its own set of negative effects on the body, such as fatigue, difficulty concentrating, and headache. Sound familiar? Make sure you are drinking enough water with your caffeinated beverages to stay hydrated.

Read labels. It is often surprising the food and beverages that contain caffeine, such as the Hershey’s bar you may reach for as a post-dinner treat. If you’re trying to limit your caffeine intake, read the labels on everything you’re consuming to make sure you’re not unintentionally consuming more than you should.

Caffeine can be both a blessing and a curse. Enjoy those caffeinated snacks and beverages, just be sure you’re doing it in moderation. For more information, check out the resources below.

References and Continued Reading