Many Australians begin their day with a cup of coffee. It’s widely viewed as a tonic with revitalising properties – each cup making us feel better. But this isn’t the same as being good for our health.
Coffee is the most widely-used stimulant in the world, with Australians consuming more than 3kg of coffee per person every year. Most of this is instant coffee, drunk at home (about 80% of total consumption) but cafe coffee is on the rise.
Coffee is a deliciously complex mixture of different compounds that come from the bean, as well as those generated or excluded in the processes of fermentation, roasting and brewing.
But the most well-known component is, by far, caffeine and each cup of instant coffee contains around 100mg of the stimulant.
Caffeine acts by blocking the (adenosine) receptors in our brain that are responsible for dulling brain activity. So by preventing this dulling, it increases stimulation. This is why coffee is so invigorating on those dreary mornings when we’d rather be in bed. It’s also one of the reasons it keeps us awake at night.
Caffeine also makes us pee more. But despite popular belief, it’s not because we’re dehydrated. Caffeine increases the urine output of habitual non-drinkers (especially in large doses) but doesn’t seem to have much diuretic effect in people who regularly take a cup or two.
Caffeine has other short-term impacts on the human body. It stimulates metabolism and modestly increases systolic blood pressure levels (by two to 12 mmHg). But again, this effect is most pronounced in non-coffee drinkers and immediately after having a cup.