Caffeine affects your sleep. No ifs, no buts.

By Karyn O'Keeffe 11/03/2011 17


Caffeine is one of the most commonly consumed psychoactive substances.  It is everywhere, in coffee, black tea, green tea, soft drinks, energy drinks, chocolate and over-the-counter medications.  We are all aware that caffeine is a stimulant; however, few of us appreciate that it can have a significant impact on our sleep.

Do any of these statements ring a bell?

Myth: Coffee has no effect on me.  I can have a coffee right before bed and have no problem going to sleep.

Fact: If you ingest enough caffeine you may have trouble getting off to sleep but in a regular consumer this is not usually where the damage is done.  Caffeine adversely affects the quality of your sleep.

Myth: I don’t drink much caffeine.  I drink tea.

Fact: Brewed products are the most variable in caffeine content, and caffeine is found in both coffee and tea, including black and green leaf.  To put content in perspective, the average cup of coffee contains 100mg of caffeine whereas a regular latté from a coffee shop like Starbucks contains approximately 250mg, maybe more.  A cup of tea contains in the range of 40-70mg and a can of cola, about 40mg.

There are a number of processes that control how and when we sleep.  One of these processes is called the sleep homeostat, which refers to our ‘need for sleep’.  In simple terms, the longer we are awake, the more we need to sleep.  This process is, in part, mediated via an inhibitory neurotransmitter called adenosine, which reduces neuronal firing rate and inhibits the release of neurotransmitters that are involved in wakefulness and arousal.  Adenosine makes us sleepy.

Caffeine is an adenosine antagonist; it blocks adenosine receptors by inserting itself instead. It enters our system reasonably quickly and is at peak plasma levels in 30-75 minutes. During the day, it gives us a quick boost in alertness and may improve attention and reaction time.

The problems arise with processing the substance. The half-life of a single dose is 3-7 hours. The more we put in our system, the longer it takes us to get rid of it.  Caffeine predominantly breaks down to paraxanthine, which has similar biological properties and also acts to reduce clearance of caffeine.  Unfortunately, the more caffeine we ingest, the more paraxanthine we produce leading to an accumulation of caffeine.  Depending on how much you are consuming and your current medical status, the half-life of caffeine can increase to anything from 11-96 hours.  Days!

So what happens when we sleep with caffeine on board?  Caffeine will cause you to have a reduced total sleep time, have less deep (slow wave) sleep and provided you’re not sleep deprived, an increased sleep latency (time to get to sleep).  Caffeine intake and poor sleep is a cycle easily repeated… you drink too much coffee today and you don’t sleep well tonight.  You wake up tomorrow morning and feel worse for wear.  Having no idea why you reach for another cup of coffee.  Sure, you fall asleep quickly each night but are you sure that it isn’t because you’ve been ruining your sleep with a steady intake of caffeine?

How much coffee should you drink?  300-400 mg is the recommended daily dose of caffeine, preferably taken before your dinner meal.  ‘No cup of tea before bed?!’ you ask.  Sadly no, try hot lemon drinks, milo (which has a very low caffeine content), or decaf versions of tea and coffee.


17 Responses to “Caffeine affects your sleep. No ifs, no buts.”

  • Discussing the caffeine content of tea without also discussing the theophylline content is meaningless. The scientifically accurate approach would be to discuss the total methylxanthine alkaloid content while acknowledging the similarities in action, and moderate differences in potency, of the individual methylxanthine alkaloids. Same goes for discussing the caffeine content of chocolate without also discussing the theobromine content.

    • I’m going to have to disagree with the ‘meaningless’ aspect of my post as the caffeine content alone in tea is enough to affect sleep. I agree, the picture is much more complex than I have presented here. I have not discussed the bioactive properties of the metabolic by-products of caffeine, nor have I discussed the other xanthine content in caffeine-containing and other products.

      My aim was simply to provide an overview for the average interested person of the effects of caffeine on sleep, while highlighting that high intake can result in retarded clearance.

  • Thanks Karyn! For years I have been telling Ben that he shouldn’t drink tea as his ‘before bed’ drink, but could never remember your scientific reasoning behind this rule. Now I have written ammunition.

  • Thank you for keeping this simple. To keep purists happy, maybe you could acknowledge that the picture is slightly more complex – without affecting your main conclusions – and point out resources for those who need to understand the full complexity?

  • You refer to the caffeine content in tea while stating that you are putting things “in perspective”. Discussing the effect of caffeine in tea without also discussing the effect of theophylline is not an accurate perspective. It is a distorted perspective. Caffeine cannot be considered in isolation in tea, or for that matter, in chocolate, because of the common mechanisms of the methylxanthine alkaloids. Why be misleading if you don’t have to be?

  • The bulk of this post seems quite sensible to me.
    Caffeine is the major xanthine in tea and coffee so I think only referring to caffeine in these products in terms of stimulatory activity is quite reasonable.
    In chocolate however the major xanthine is theobromine so it would be best not to relate the stimulatory properties of chocolate only to caffeine.
    There is roughly 7 times the amount of theobromine in chocolate as there is caffeine, but it’ stimulatory effect is roughly 10 times weaker, so in chocolate caffeine and theobromine in chocolate have similar effects.

  • As a regular non-scientist type person who has just quit coffee (but not green or black tea!) I find this post really interesting and understandable. I have no idea what Rosalind is on about and if the post had included all that detail I probably wouldn’t have read it.

  • Thanks for clearing the myths of how caffeine affects the quality of sleep, so even though some people claim that they can sleep when drinking coffee, they don’t actually sleep as good. Caffeine increases the number of nocturnal awakenings

  • Hi im a cola addict and was always worried about the sugar content and not the caffine…until lastnight….i wake up early every morning very anxious and jittery..i get off to sleep ok but i dream alot and most of the time they make me feel worse…it dawned on me today about the amount of cola i drink and the affects of the caffine..thank you for confirming what i thought..i shall be swapping for caffine free cola and i shall keep a diary of my findings, thank you

  • Am on a caffeine-free drink diet and have been for six days. That’s six days of the most awful headaches ever – for improvement of sleep purposes I will continue, and will await eagerly for the headaches (withdrawal?) to leave.

  • I have had sleep problems all my adult life. I only 18mths ago discovered that the cause for me was my tea habit (8 – 12 cups of tea with milk a day) I would have trouble getting to sleep, my mind would race and my sleep was very intermittent, with early waking – like 3 am the staying awake. I pretty much stopped drinking tea, allow myself one cup first thing in the morning, then just drink herbal teas or water. Over a period of 6 months my sleep has improved tremendously. There is no doubt for me that tea was a major factor. If only I had realized that 30 years ago. Thanks for your post and info, you’ve definitely hit the mark

  • good read explaining clearly the impact of tea/coffee and sleep, thanks. that said, you are off the mark with Milo – it may have minimal caffeine but it contains plenty of sugar, which will result in a sugar low for people circa 2am – which will jack up their cortisol levels and keep them awake, usually for a few hours. so drop the milo and the ‘decaffeinated’ tea and coffee, as they also still contain caffeine. cheers

  • Is it possible that a regimen of one single cup of coffee every morning can cause chronic sleep loss and fatigue over a long period of time? I go to bed at 11:00 PM and wake by 4:00AM every morning. I lay in bed with my eyes closed wanting to sleep more but with my mind racing. Am I craving my morning coffee? I am 53, male 6’1″ and 155lbs. Slim, hard-gainer. Thanks!

    • I would expect that the majority of the caffeine would be out of your system by the time you go to bed, but there are individual differences in tolerance and metabolism. Unfortunately, I’m not enough of an expert to comment on how much caffeine is likely to be in your system at bedtime. The best way to find out if caffeine is affecting you is to experiment. Give yourself two weeks without your morning coffee (without changing anything else that might affect sleep) and see if your sleep is improved. It sounds like you might have insomnia. If this has been a long standing issue and removing caffeine makes little difference, you may like to talk to a sleep professional.

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