Sleep deprivation is a major problem. Over time, it will cause significant metabolic changes, such as an increase in appetite, and cravings for salt and sugar. How many of us reach for a cupcake, or a packet of crisps, when we're tired?

So, the best reason to take a siesta is to ensure that you're getting enough sleep. It's especially useful to take a nap or short siesta before a high-pressure situation, such as travel or a major meeting. If you drink two coffees, and then sleep for 20 minutes – no longer, or you'll find yourself entering a deep sleep – and on waking the caffeine will just be kicking in, so you'll feel doubly alert.

A lot of research has been done into the potential health benefits of Spanish-style siestas. In 2007, a study by Greek researchers appeared to offer evidence that regularly taking a nap in the afternoon protected you against death from heart disease, but it's very difficult to separate factors such as sleep from the other potentially beneficial aspects of the Mediterranean lifestyle.

People who regularly find themselves feeling sleepy in the afternoon, however, might need to look at how much sleep they're getting, and whether they have any underlying sleep problems. And regular sleep times are actually much more beneficial than siestas. When it comes to sleep, routine is good for us – we should all aim to get to bed at the same time each night, and get up at the same time each morning.

• Mary Morrell is professor of sleep and respiratory physiology at the National Heart and Lung Institute, Imperial College London