The Effect Of Coffee On Your Sleep

Last updated: May 6, 2019

The information on this website is not intended to replace a one-on-one relationship with a qualified health care professional and is not intended as medical advice. Read our full medical disclaimer.

Coffee and other caffeinated drinks are widely used to fight sleepiness and drowsiness, primarily in the morning but also at some other times of the day. For most people drinking coffee in the evening will make them go to bed a lot later than usual but having coffee at, say, 6pm will not make any difference.

Science shows us that even an afternoon cup of coffee can disrupt your sleep without you being aware of it. It also shows that the amount of caffeine in a single cup of coffee prepared in the same coffee shop can vary greatly. Luckily there are some steps you can take to make caffeine work well for you and to avoid having sleep disturbances.

Coffee and caffeine

Coffee is one of the most popular drinks worldwide. It contains caffeine – about 100-200mg per 8oz cup – which makes coffee a stimulant, which means that it helps us concentrate and shake off tiredness.

Coffee and caffeinated tea make up for about 95% of caffeine consumed in the world. Other sources of caffeine are cocoa, dark chocolate, energy drinks, soft drinks like Coca Cola, and even some ice cream types. You can check for the presence and the amount of caffeine at the back of these products.

Some companies produce and sell pure powdered caffeine – however, the FDA warns about these products as taking powdered caffeine makes it extremely easy to consume an excessive amount of caffeine, which can be seriously dangerous for one’s health.

Adults do not need caffeine in their diet but can safely use it in moderate amounts – it is recommendable to have a maximum of about 300-400mg of caffeine per day (that’s about 3 8oz cups of coffee). Please bear in mind that not everyone reacts to caffeine the same and as 300mg may be safe for one person, it might be too much for someone else. Children and pregnant women are advised against consuming caffeine by the FDA.

Here we will talk about coffee as a representative source of caffeine because, for the majority of Americans, it is the main source.

Can you know for sure how much caffeine you’re taking in?

There are some general guidelines on how much caffeine is contained in certain types of coffee, but research shows that after taking the exact same type of coffee from the same machine and the same coffee shop can give you huge differences in the milligrams of caffeine present.

In the study, researchers were taking coffee from the same source for six consecutive days and they tested it for the amount of caffeine. The cups were 16oz, about the size of two regular cups. Caffeine amount varied between 259mg and 564mg per cup.

It is generally said that a 8oz cup contains about 100mg of caffeine. When buying a 16oz cup we might expect we’ve got 200mg of coffee thinking we can have some more, according to the recommendations. The truth might be that in that single cup you have consumed almost 600mg, which is considered an excessive coffee intake.

As each coffee bean and each method of making coffee gives you a different amount of caffeine, you should have this in mind when going for coffee. On the other hand you can expect a can of soda to always contain approximately the same amount of caffeine because its levels were closely monitored in the factory.

How does coffee affect your brain?

Caffeine blocks the effects of the brain chemical that makes us sleepy (neurotransmitter adenosine). It also speeds up the heart rate and makes us more alert by increasing adrenalin and dopamine.

Caffeine binds to adenosine receptors in the nerve cells and thus blocks it by taking its place. The body might start producing more adenosine because it’s important to inform our brain about the needed rest time – and because of this adenosine increases. However, when the caffeine effect wears off we might feel a sudden ‘sleepiness attack’.

This sudden sleepiness is something you can expect to feel if you drink coffee to boost your wakefulness after many hours of being active. However, if you drink coffee in the morning you’re likely to feel energized, concentrated, and productive.

Too much caffeine

Some side effects of taking an excessive amount of coffee are diarrhea, sweating, high heart and breathing rate, and muscle tremors. You may feel anxiety and become overly sensitive to your surroundings.

You can also become addicted to coffee and just like with other addictions, there are some symptoms that follow its absence, like headaches and bad mood paired with low energy and excessive sleepiness.

How does coffee affect your sleep?

Caffeine and sleep cycles

In one sleep cycle, you go through four stages of sleep – two light stages, deep sleep, and REM sleep. Each of them is important for our health and wellbeing.

Light sleep consolidates our motor memory, deep sleep restores tissues and maintains the brain and the immune system, and REM sleep regulates our emotions – just to name some of their benefits.

Caffeine prolongs light sleep, increases the number of awakenings, and shortens deep sleep. REM sleep is mostly unaffected. Without deep sleep a person is likely to feel a lack of focus and increased daytime sleepiness, which calls for an additional cup of coffee.

Caffeine and perceived sleep quality and quantity

Sleep usually doesn’t go well with caffeine. A study has shown that even if you consume caffeine 6 hours prior to your sleep time you’ll experience disrupted sleep – and this means increased sleep latency (the time you need to fall asleep), shorter total sleep time and poorer sleep quality.

Twelve healthy young men and women without sleeping problems were chosen to participate in the study. They were told to keep sleep diaries, but sleep monitors were also used. The scientists measured how caffeine affected their sleep after consuming a caffeine pill at three different times – bedtime, 3 hours prior to sleep, and 6 hours prior to sleep. The amount was 400mg of caffeine (about 3-4 8oz cups of coffee).

Study participants reported poor sleep after taking caffeine at sleep time and 3 hours prior to bed, which was confirmed by the sleep monitors. They didn’t report any sleep problems after taking the pill 6 hours before sleep, while the sleep monitors still showed the poor sleep quality.

In all three cases the sleep time was reduced by 1 hour.

It is well-known that it takes our body about 6 hours to get rid of about half of the caffeine we take in. It’s called the 6-hour half-life. This means that the study participants are likely to have had about 200mg of caffeine still circulating in their system even after 6 hours – the dose which disrupted their sleep.

What we should learn from this study is not to rely on our personal perception of sleep quality, but rather to cut back on caffeine at the right time. You can have strong caffeinated drinks in the morning but make sure to lower the amount of caffeine you take in as the day progresses in order to have good sleep.

Caffeine and circadian rhythm

Caffeine can delay our biological clock – also called circadian rhythm. It is the daily rhythm of our bodies which tells us when we are going to sleep and wake up as well as manages many other processes, like hormone release.

It was found that caffeine can ‘reset’ the circadian clock, delaying it by about 40 minutes. Just for comparison, exposure to bright light, one of the main cues which set the circadian clock, delays it by only 20 minutes.

Does the same amount of caffeine affect everybody equally?

It doesn’t. A 6’5” tall young man will not respond to a cup of coffee in the same way as an elderly lady – and there are a number of reasons for that.

One of the reasons seems to be genetics and the way in which the body metabolizes caffeine. Some are genetically more resistant, and some more sensitive.

Age and body weight also may play a role in how the body responds to caffeine.

Those who take caffeine on a daily basis are less sensitive to its energy-giving effects but not less resistant to sleep problems caused by it.

Can coffee make you sleepy?

Some people have a strong urge to sleep soon after having a cup of coffee. It could be because of the adenosine buildup and its sudden, strong effect as soon as the caffeine wears off. It could also be because their coffee is too sweet (if they use sugar or syrup) and as the body quickly burns sugar, it suffers an energy slump.

Caffeine causes us to urinate frequently and could make us dehydrated, which in turn makes us sleepy. This happens because the blood flow slows down due to a lack of water and the blood vessels narrow (vasoconstriction occurs) due to caffeine. This way, the blood brings less oxygen to our body and we become sleepy.

Some people with ADD/ADHD complain about having to sleep as soon as they drink coffee, probably due to how caffeine reacts with the medication they are taking.

Do some people combine coffee and sleep? Coffee naps

Recently there have been many studies which look into how we can boost our energy by actually combining sleep and coffee. As caffeine takes about 15-30 minutes to kick in, you can drink a coffee and take a quick nap before the caffeine becomes active in your system.

After waking up, most of your adenosine will be cleared out due to sleep or blocked by caffeine, which should give you a feeling of freshness.

This kind of nap is a good solution if it’s not late in the afternoon and if you are racing against time to manage all your tasks successfully.

Should I avoid coffee to get a good night’s rest?

If you use coffee moderately and at the right time then there’s no reason to avoid it. Dr. Michael J. Breus, author of many sleep articles and books, recommends stopping your caffeine consumption at 2pm. Inform yourself about which caffeine-containing food and drinks you regularly consume and try to avoid them in the evening.

The National Sleep Foundation also advises against the consumption of alcohol and cigarettes before bedtime since they impair your sleep.

Additional resources

  1. Drake C, Roehrs T, et al. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. JCSM. 2013. https://www.ncbi.nlm.nih.gov/pubmed/24235903 Accessed April 4, 2019.
  2. Roehrs T, Roth T. Caffeine: sleep and daytime sleepiness. Sleep Med Rev. 2008. https://www.ncbi.nlm.nih.gov/pubmed/17950009 Accessed April 4, 2019.
  3. Clark I. and Landolt H.P. (2016) Coffee, Caffeine, and Sleep.Sleep Med Rev. 2008. https://www.ncbi.nlm.nih.gov/pubmed/26899133 Accessed April 4, 2019.
  4. Burke T. M, Markwald R. R, et al. Effects of caffeine on the human circadian clock in vivo and in vitro. Science Translational Medicine. 2015. http://stm.sciencemag.org/content/7/305/305ra146 Accessed April 4, 2019.
  5. Ogeil R.P. and Phillips J.G. Commonly used stimulants: Sleep problems, dependence and psychological distress. Drug & Alc Dep. 2015. https://www.ncbi.nlm.nih.gov/pubmed/26049205 Accessed April 4, 2019.

The information on this website is not intended to replace a one-on-one relationship with a qualified health care professional and is not intended as medical advice. Read our full medical disclaimer.