Wristwatches are truly out of fashion. Sales have been falling over the past decade and according to a recent YouGov survey, the majority of 16-34-year-olds have given up the traditional timepiece in favour of a smartphone. However, in a bizarre twist of irony, our new digital timekeeper could be disrupting a far more important clock – the body’s very own internal clock. And that is something you definitely don’t want to do.

You probably hadn’t realised it, but your body is keeping careful track of time. There is a tiny biological clock inside your brain – just behind the eyes – that is telling you when it is time to wake up, when to eat and when to go to sleep. It controls what is called our ‘circadian rhythm’ – and keeping in sync with it is key to having a productive day.

For example, have you ever wondered why you feel so sluggish after lunch? You can blame your internal body clock for that: in the early afternoon your body wants you to go and take a siesta. Both mental and physical abilities are orchestrated by the circadian rhythm. You can think most clearly in the late morning (between 10am and 11am), while your athletic performance peaks in the early evening. My suggestion would be to do your most important work before lunch, don’t arrange any meetings early afternoon, and attempt your Olympic Gold at 6pm.

Going against your circadian rhythm is unpleasant: just try getting jetlagged or doing a nightshift and see how that feels. Worryingly, today’s modern clock – the smartphone – may very well be making us feel jetlagged all of the time.

A survey published this month shows that 78 per cent of British adults check their smartphone or use a similar electronic device just before going to sleep. But by peering at a digital screen before bed, we are actually shining an intense blue light into the back of the eyes that confuses the body clock into thinking it is day again. Levels of the sleep hormone melatonin are supressed and getting to sleep is harder. Ultimately, the next day’s circadian rhythm is knocked off kilter, and alertness, productivity and mood will be affected. Worryingly, long term poor sleep patterns can predispose you to suffer from diabetes, heart disease and obesity.

Perhaps mercifully, the wristwatch’s number isn’t up just yet. The arrival of the internet-enabled ‘smartwatch’ is set to be the next must-have gadget, and will drag the 400-year-old invention into 2014. I sincerely hope though, that for sleep and sanity’s sake, all the models have a low-light night time setting.

Then again, perhaps simpler to just know the time when we turn off our electronic devices… and use something else to check the time.