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 lattÃ© 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.