Coffee is no good for you – that’s the received wisdom, at least. It is full of caffeine that’s addictive and can make you bounce off the walls, give you headaches and disrupt sleep. Excessive consumption has been linked to heart disease and cancer. And although coffee increases alertness and focus, the effects are short-lived. Users quickly become tolerant: people who regularly drink coffee are no more alert on average than those who don’t. For regulars, the morning brew merely reverses the fatiguing effects of caffeine withdrawal, bringing them back to a baseline level of alertness.

Sounds like one to avoid, then. But Kirsty Pourshahidi of the Northern Ireland Centre for Food and Health in Coleraine, UK, thinks that’s overbrewed. “Having looked into it, I don’t feel so bad having three or four cups of coffee a day,” she says.