Coffee on the Brain
On a normal day I drink 2 cups of coffee, based on those neat little capsules that are everywhere. I don't drink any coffee after about midday as I have convinced myself that it would have a negative impact on my sleep. My wife on the other hand, would also drink 2 to 3 coffees in a day, but irrespective of time and having a cup in the evening does not seem to negatively impact her sleep at all. So what is going on? Does it really matter how much caffeine I consume and when I consume it?
Lets be clear, caffeine is a psychoactive drug owing to its mood-enhancing and stimulatory effects. The key compound it acts on is called adenosine. Adenosine is made in the body and locks onto certain brain receptors resulting in muscle relaxation and sleepiness - hence why you get tired as the day progresses - levels of adenosine increase throughout the day from physical work and brain use. However, adenosine also interferes with mood-improving compounds such as dopamine. Dopamine has numerous functions, but probably best known for creating feelings of pleasure, reward and motivation.
When you wake up in the morning, you probably feel a little bit groggy like me. But overnight, the body has metabolized most of your adenosine, so once you pull yourself together, the body is awake and ready for work. I usually have a cup of coffee early on. So, the caffeine in my coffee is absorbed in the small intestine and enters my blood. Blood concentration of caffeine from my coffee peaks about 2 hours after drinking it. The caffeine reduces the ability of adenosine to lock onto the relevant brain receptors. It also promotes the release of dopamine and glutamate (yes, another upper hormone) and so overall, I feel alert and pretty good, these feelings peaking about 2 hours after my morning coffee. (There are other short-lived and usually positive physiological impacts of caffeine, hence why athletes consume caffeine through coffee or via supplements)
However, as the day progresses, the impact of the caffeine reduces as it gets metabolized and bam! The adenosine hasn't gone away, but rather the levels have been increasing as I do work. Indeed there can be a rush of adenosine binding to receptors in the brain and quite suddenly I can begin to feel sleepy. Another dose of caffeine will of course inhibit adenosine again and I'll feel more alert.
You can see now, that if I imbibe caffeine later in the day it can absolutely impact my sleep as the ability for adenosine to tell my brain it's time for sleep is reduced. So, I can see how it impacts me, but what about my wife and those other folk for whom caffeine does not seem to impact their sleep patterns?
Well, it turns out that caffeine impacts people in different ways - its your genetics. Indeed, if you consume enough of it, the body will build a tolerance to it and the type of effects discussed above are significantly reduced. Additionally, caffeine is ultimately metabolized in the liver, and some people can metabolize it much quicker than others, so again, the impact of caffeine is reduced. Smokers can metabolize caffeine very quickly - perhaps somewhat explaining the higher levels of coffee that smokers drink.
That's it! So, I know my sleep is impacted by caffeine and I'll continue to minimize my coffee intake later in the afternoon or evening. Oh yeah, don't forget, many foodstuffs also contain caffeine and in particular energy drinks and certain fitness supplements are crammed with it.
