Caffeine and Sleep: Does Caffeine Affect Sleep?

By: SleepScore Labs  |  February 10th, 2017

Every morning, you walk downstairs and head for that glistening coffee pot to make a steaming hot cup of joe. While that first morning cup probably tastes amazing, the feeling that comes from drinking coffee can be even more enticing.  

Caffeine is a stimulant with powerful physical and mental effects. To promote healthy sleep, it’s crucial to understand how caffeine and other stimulants affect the body, so you can manage your consumption to avoid sleep problems. 

This article will take you through what caffeine does to your body, how it may affect sleep, and how you can consume caffeine so it’s less likely to interrupt your sleep quality. 

How Does Caffeine Affect Sleep? 

Caffeine is a psychoactive substance that many people consume to stay awake, improve alertness, and boost mental performance. However, many may overlook or be unaware of how their caffeine intake affects their sleep health. 

Caffeine stimulates your body’s central nervous system, increasing alertness and reducing fatigue.  

Numerous studies show that it may keep you awake even when you’d rather be asleep. Experts recommend caffeine as an effective intervention for keeping night-shift workers awake and alert when necessary.  

2021 study on the impact caffeine intake has nighttime sleep in young adult men suggests that caffeine can reduce how quickly a person falls asleep, reduce their total sleep duration, and the quality of sleep they get. These effects happen especially when it’s taken around evening time. However, if consumed early in the day (no later than 2PM for most people), caffeine is unlikely to disturb sleep quality or sleep architecture (the structure of a person’s sleep cycle) in people who otherwise follow healthy sleep hygiene. 

Interestingly, a 2013 study explored the impact of caffeine on nighttime sleep when taken 0, 3, or 6 hours before bedtime. It found that having even a moderate amount of caffeine 3 and even 6 hours before bed significantly impaired sleep. 

The study then recommended that people avoid caffeine at least 6 hours before bedtime so that its effect doesn’t disrupt quality sleep at night.  

Authors of a 2018 study investigating the effects of caffeine on sleep quality and daytime functioning asked important questions worth noting: “Can caffeine undo the harm it potentially causes through reducing the quality of overnight sleep?”  

It’s well established that caffeine improves daytime alertness and cognitive performance but also impairs sleep quality. Numerous evidence also shows that sleep improves daytime functioning and attention. And poor sleep causes excessive daytime sleepiness, fatigue, and sluggishness. 

So, is caffeine indeed an antidote to lethargy, or is caffeine impairing your overnight sleep quality, making you sleepy during the day to the point where you need yet another caffeine boost? Does caffeine consumption merely reverse the potential harm it causes or improve daytime alertness? 

According to an older study, evidence tilts to the position that when sleep-deprived, caffeine merely restores performance impaired by poor sleep rather than improve performance.  

What Does Caffeine Do to Your Body? 

People worldwide consume caffeine in its different forms (caffeinated soda, tea leaves, coffee beans, kola nuts, coffee, energy drinks, tea) daily. About 90% of the US population consumes caffeine almost every day.  

Caffeine generally improves reaction time, memory, alertness, mood, and physical and cognitive performance. It stimulates the production of adrenaline, an alertness-boosting hormone linked to your body’s fight or flight response. An increase in adrenaline raises your heart rate and breathing and brings on a state of increased vigilance and alertness.  

79% of participants of a study reported that they consume caffeine to feel awake, 68% said they enjoyed the taste, 31% said to help boost concentration, 27% consumed it to feel energized, 18% used caffeine to improve their mood, while 9% consumed it to manage stress. 

Caffeine consumption is generally considered safe for the average adult when taken moderately—about three to four cups a day. However, the US Food and Drugs Administration (FDA) notes that what’s considered moderate or healthy varies from person to person. But they recommend not having more than 400 milligrams a day (four or five cups of coffee) as this amount is not linked with any adverse effect on the body.  

For most people, the body absorbs caffeine within 45 minutes, and its effect can last for up to 16 hours after initial intake, depending on different internal and external factors.   

Caffeine also blocks adenosine, a chemical in your body that helps regulate the body’s internal drive for sleep. This is because adenosine and caffeine have similar chemical structures, so caffeine binds to the same receptors in the brain that adenosine would usually bind to in order to signal sleepiness — but without inducing sleepiness. In turn, it prevents the drowsiness that occurs as the levels of adenosine in the body increase. Additionally, caffeine alters sleep architecture, the overall nightly distribution of sleep among the different sleep stages.  

Over-caffeinating can reduce time spent in deep sleep, the phase that is critical for physical and mental rejuvenation. 

People can become dependent on caffeine and be unable to do without caffeine even when it starts to impair their health and wellbeing.  

A person may build up a tolerance to caffeine such that they may need larger doses to produce the same effects it used to have when taken in smaller amounts. A person may also experience withdrawal symptoms when they stop taking caffeine. Some of these symptoms include fatigue, headache, poor mood, sleepiness, and difficulty concentrating. 

How Long Do the Effects Last? 

Caffeine kicks in quickly. Evidence suggests that 99% of people start experiencing the effect of caffeine within 45 minutes of taking it. But it stays in the body longer than you may expect.  

Half of the amount of caffeine you take may remain in your system for six or more hours. This is what experts describe as caffeine’s half-life, and it is not a fixed figure. It is the amount of time it takes caffeine to work its way out of your system. This can vary from four to six hours or more but seems to average around 5.7 hours. But there’s also evidence that suggests that caffeine’s effect can last in the body for up to 16 hours.  

How Long Before Bed Should I Stop Consuming Caffeine? 

When taken close to evening time, caffeine may disturb how quickly you fall asleep, sleep quality, duration, and intensity.  

2013 study recommends limiting caffeine to at least 6 hours before bedtime to prevent it from affecting a good night’s rest. 

How Can I Tell If Caffeine Is Affecting My Sleep? 

If you’re a caffeine lover, you might be curious to know if your caffeine consumption impacts your sleep health. 

Here are some ways to tell: 

  1. It takes you longer than usual to fall asleep 
  2. You wake up frequently at night  
  3. You don’t feel like you don’t feel well-rested when you wake up 
  4. You always need an energy boost to start your day 
  5. You find yourself feeling sleepy during the day 

However, if you’re experiencing sleep disturbances or problems staying alert and functioning during the day, consider speaking with a doctor who may provide a more accurate diagnosis and prescribe treatment options for your case.  

Next Steps 

Moderation is the key to kicking sleep deprivation that’s caused by drinking too much caffeine. That morning cup of coffee is typically fine, so long as you’re not having trouble sleeping at night. Many people can manage moderate caffeine consumption early in the day without compromising sleep. A general guideline is to curtail caffeine consumption by 2 PM. 

Another great strategy is to monitor how much caffeine you’re drinking each day. Start the day with the most highly caffeinated beverage, and gradually taper down from there. Switch to a half-regular, half-decaf cup of coffee, or tea, before forgoing caffeine altogether for the remainder of the day. It’s also important to remember the amount of caffeine in popular drinks can vary widely. An 8-ounce cup of coffee contains approximately 100 milligrams or more of caffeine. A latte can typically have anywhere from 60-175 mg of caffeine, while a single-ounce espresso may have 47-75 mg. Cola drinks usually have between 25-45 mg of caffeine, while an 8-ounce cup of green tea contains 24-45 mg of caffeine. 

If you decide to give up caffeine altogether, try eliminating it gradually. Giving up caffeine abruptly can lead to fatigue and sluggishness and may cause headaches. These effects are short-term and won’t have any lasting consequences on your overall performance. Nevertheless, it can be easier and less disruptive to taper down your caffeine consumption gradually. 

Moderating caffeine consumption and other stimulants is an essential part of a healthy daily sleep routine and a long-term plan for sleep health.


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