There's a science behind your coffee addiction

My morning coffee has become a pretty essential part of the day. Without it I'm far less pleasant to be around (just ask my husband!). Why do I love my coffee so much? It's really all about the caffeine.

Caffeine is a stimulant - mostly because of how it reacts with different receptors in our brains. Our brain contains a bunch of receptors for a molecule called adenosine. Adenosine is produced from the break-down of a molecule called ATP.

For anyone who's taken a biology class, you'd know ATP as the "energy molecule". While we're awake and our brains are working hard (like during the exams my students are sitting this week) they use a lot of ATP, and make a lot of adenosine.

This adenosine binds to adenosine receptors in the brain, and slows down neural activity, making you sleepy.

What does this have to do with caffeine? Well, caffeine is a sneaky little molecule, and it also likes to bind to these adenosine receptors. When it does, it means adenosine can't, so you don't get the sleepy effect, and instead feel nice and wide awake.

It also helps that caffeine triggers the release of adrenaline - commonly known as the "fight or flight" hormone - giving you a nice burst of energy.

And to make it even better, caffeine also stimulates the production of dopamine, a neurotransmitter that plays a role in motivation and reward (and may explain why it's just a tad addictive). Not a wonder we love a good dose of caffeine in the morning to get us going!

These wake-me-up, feel-good effects of caffeine are pretty well known. What's interesting is that these side effects last much longer for some people than they do for others. There's a key gene that's involved in metabolising caffeine, called CYP1A2. Different people have different versions of this gene, which mean that the enzyme that's produced works slightly differently in different people.

Depending on which version of the gene we have, we're able to metabolise caffeine slowly, or more quickly - and those side effects will either last for a long time, or a shorter time.

Caffeine is the most widely used psychoactive drug in the world. Yep - next time you're sipping on that cappuccino, or double-shot soy iced latte, remember you're ingesting a healthy dose of a mind-altering substance. And gosh, doesn't it feel good.

Dr Mary McMillan is a lecturer at the School of Science and Technology, University of New England