When we are awake, a chemical called adenosine slowly accumulates in our brain. So this adenosine binds to receptors which slow down brain activity — ultimately, the more adenosine there is, the more tired our brain feels. Which makes sense, as the longer we are awake, the more fatigued we become. Conversely, while we sleep, the concentration of adenosine declines, gradually promoting wakefulness. However, it turns out that the caffeine in the coffee is incredibly similar to adenosine in structure. The caffeine works it is way through our bloodstream and enters into the brain, where it starts to compete and binds with adenosine receptors. So the amount of adenosine bind with receptors will be decreased, and ‘sleepiness’ effect is not felt, which is great feeling for us.
However, with long term use of caffeine, our brain responds by creating more adenosine receptors — which means more caffeine is required to get the same response as before. It also means that when we try to quit drinking coffee or miss our daily intake, we might experience
some withdrawal symptoms and feel more tired than we would have before we ever drank coffee!
Also, caffeine does not stop just there. Caffeine also can stimulate the production of adrenaline the Flight hormone?. This increases our heart rate, gets our blood pumping, and even opens up our airways. Furthermore, it can increase Dopamine levels by stopping its reabsorption in our brain, which makes us feel happy. This effect is similar to cocaine, just in a minor degree. It makes coffee moderately addictive.
So can we drink too much coffee?
The lethal dose of caffeine is around 150mg of caffeine per kilogram of our body weight. This means if our weigh is 70kg, it would require 14,000mg of caffeine to overdose us. In reality, an average cup of coffee contains roughly 150mg of caffeine, meaning we approximately need 70 cups of coffee to kill us.
you’ll be feeling half of the effect at that point. Another 6 hours after that, you’ll have 37.5mg — in the system leaving more room for adenosine to go back to action. Which is why you may reach for another cup throughout the day, to maintain that energetic feeling.
By- Chamika Siriwardhana
University of Sri Jayewardenepura