Does coffee really give you energy? Find out what the truth is

Adenosine is part of the system that regulates our sleep-wake cycle and part of the reason why high levels of activity lead to fatigue. As we go about our days and do things, adenosine levels rise because it is released as a byproduct as energy is used in our cells.

Adenosine binds to its receptor (part of the cell that receives signals) that tells the cells to slow down, making us feel sleepy. This is why you feel tired after a day of activity. While we are sleeping, energy use falls by reducing adenosine levels as it is converted into other forms.

If you still feel sleepy when you wake up, caffeine can help, for a while. It works by binding to the adenosine receptor, which it can do because it's a similar shape. Instead, it simply fills the spots and stops adenosine from binding there. This is what removes the feeling of drowsiness.

Caffeine can also increase levels of cortisol, a stress hormone that can make you feel more alert. This may mean that caffeine feels more effective in the morning because you already have a natural rise in cortisol when you wake up. The effect of a coffee right out of bed may not seem so powerful.

While there is no proven harm in drinking coffee on an empty stomach, coffee with or after a meal can hit you more slowly. This is because food can slow down the rate at which caffeine is absorbed.

Caffeine can be helpful, but it's not magic. To create energy in our body, we need enough food, water and sleep.