Coffee and what it does to your body - BBC World Service

By the time you finish watching this video, eight million cups of coffee will have been  drunk all over the world. Coffee has been consumed for at least 1,500 years and some say its impact is so great that it helped fuel the Enlightenment, which gave rise to some of the big ideas that underpin the world as we know it. The main active ingredient of coffee is caffeine, which is considered the most widely consumed psychoactive drug on the planet.

So where does coffee come from and what does it do to us when we drink it? Coffee comes from the fruit of the Coffea arabica plant that originated in Ethiopia. One story claims a ninth Century goat herder called Kaldi, saw his goats were more full of energy after eating coffee berries — so he had a bite too.

Historic records suggest the Sufis of Yemen roasted the seed of the coffee berry to create the beverage we recognise today. In the 15th Century, the first coffee houses began to appear across the Ottoman Empire before spreading to Europe in the following centuries. Coffeehouses in Europe became a space for discussing business, politics and new ideas.

One academic - Jurgen Habermas – even says without coffee we might not have had the Enlightenment. Philosophers like Kant and Voltaire - who  is said to have drunk as many as 72 cups a day - started to question the Catholic Church’s interpretation of the world. Instead they looked to science, believing that everything in the Universe could be rationally explained.

This so-called Age of Enlightenment radically changed the world as we knew it. It led to the overthrow of monarchs, the growth of democracy, and numerous scientific discoveries. Coffee also fuelled the slave trade.

The French used slaves from Africa on plantations in Haiti and by the early 1800s Brazil was producing a third of the world’s coffee using African slaves. Did coffee give rise to capitalism too? Companies started giving away coffee to their workers and eventually let them have coffee breaks.

This wasn’t an altruistic move. They were trying to increase worker productivity. Fast forward to the present and two billion  cups of coffee are consumed every day.

It’s a $90 billion a year industry. And, more than that, it is a fundamental social part of everyday life for billions of people. So how does coffee impact the body?

When caffeine enters your digestive system, it is absorbed via the intestine into the bloodstream. But the effects only start when caffeine hits the nervous system. This happens because caffeine has a chemical structure very similar to that of a substance produced by our own body: adenosine.

Caffeine binds to the body’s adenosine receptors, which can be found on the surface of nerve cells. It's like a key opening a lock. Adenosine is known to slow down the sympathetic nervous system - it reduces your heart rate and generates a state of drowsiness and relaxation.

By blocking these receptors, caffeine generates the opposite effect. Your blood pressure, for example, may increase slightly, especially if you are not used to drinking coffee often. The same goes for brain activity: caffeine stimulates the brain, suppresses hunger and helps you stay in a state of alertness, so you can concentrate for longer.

Caffeine can have a positive impact on your mood, inhibit feelings of fatigue, and can improve physical performance. So, many athletes use it as a supplement. These effects can last between 15 minutes and two hours.

The body removes caffeine five to 10 hours after consuming it but caffeine’s residual effects can last even longer. If you want to optimise caffeine's effects on your body, experts suggest abstaining from caffeine in the afternoon - so your cup of coffee the following morning has more impact. Coffee also requires care when it’s drunk.

For healthy adults, the recommended [maximum] limit is 400 milligrams of caffeine a day. That’s about four or five cups of coffee. Exceeding this limit can lead to side effects such as insomnia, nervousness, anxiety, tachycardia, stomach discomfort, nausea and headache.

Toxic effects, like seizures, can be seen after the rapid consumption of around 1,200 milligrams of caffeine - that’s the equivalent of around 12 cups of coffee. Of course these limits vary from person to person: some people are genetically more sensitive to caffeine. But when drunk in moderation, coffee can be good for your health.

For instance, it’s associated with a reduced risk for type 2 diabetes, cardiovascular disease, some cancers and Parkinson’s. And these health gains aren't just linked to caffeine. Coffee has other beneficial substances, such as chlorogenic acid, a potent antioxidant that may reduce the risk of many diseases.

So next time you grab a cup of coffee, you might not look at it the same again.