The next time you can’t sleep, your brain whirring over class assignment, the solution could be simple – move your mobile phone off the bedside table and out of your bedroom altogether.
Eight out of ten of us keep our mobiles on overnight according to Ofcom, and around half use our phone as an alarm clock, a survey found.
But experts are concerned about the effect this is having – at the very least it makes us ‘hypervigilant’ so our sleep is more likely to be disturbed and we end up not getting enough of the restorative sleep we need. But it might also trigger insomnia and other sleeping problems.
Most people will sleep better if the bedroom is kept free of mobile phones and other electronic devices, says Dr Guy Meadows, insomnia specialist at The Sleep School, London. Dr Meadows leaves his smartphone in the kitchen at night.
More controversially, there are suggestions that sleeping with your mobile by your bed may cause dizziness and headaches.
The main problem with mobile phones in the bedroom is light, particularly the kind produced by the bright, high-quality screen on modern phones.
It interferes with the body’s natural rhythm, effectively tricking our bodies into believing it’s daytime, according to Dr Charles Czeisler, a professor of sleep medicine at Harvard University.
Light stimulates cells in the retina, the area at the back of the eye that transmits messages to the brain. The light-sensitive cells inform our body what time it is, explains Dr Meadows.
‘This controls the release of the hormone melatonin, which makes you feel sleepy, and the waking hormone, cortisol.’
All artificial light, whether from standard light bulbs or fluorescent strips, is thought to inhibit the release of melatonin, keeping us awake longer. But light from mobiles may have a greater effect.
Why? Most of us think of normal light as white, but it’s made up of different colours of varying wavelengths, explains Professor Debra Skene, a neuroendocrinologist at the University of Surrey.
And the light emitted by phones, tablets and e-readers contains a great deal of blue – this means it has a more stimulating effect.
‘We know that because of a pigment called melanopsin, the cells in the retina are most sensitive to blue light,’ says Professor Skene.
This is why reading something on a phone or tablet before bed could be more likely to keep you awake than reading a book with your bedside light – and it’s why sleep experts advise a ban on screen time two to three hours before bed.
TV screens also emit blue light, but with mobiles the light source is closer to your eyes.
Even short bursts of light – from a message alert or checking your phone – may have an effect. A 2011 study at Stanford University in the U.S. tested the effect of a total of just 0.12 seconds of light exposure during the night. Participants were exposed to pulses of light lasting two milliseconds each for an hour. This delayed the bodyclock and people became more alert.
‘This, along with other studies comparing intermittent and continuous light, suggests the first part of any light exposure is more effective on making the body more alert than the later part of light exposure,’ says Professor Skene.
And because of the way we sleep, having a mobile by the bed means if we do wake up in the night, we’re more likely to stay awake.
‘If you then check your phone, you’ll be stimulating the cognitive parts of your brain, too – which really will stop you sleeping,’ adds Dr Meadows.
Four in ten smartphone users say they check their phone if they’re disturbed by it in the night.
‘There’s not always something new or interesting every time you check your messages – but there might be,’ explains Tom Stafford, a lecturer in psychology and cognitive science at Sheffield University.
Sleep expert Dr Neil Stanley adds: ‘In order to get a good night’s sleep, you have to feel safe and not worried about anything. By having your phone close by at night, you’re subconsciously saying you wish to attend to that phone.
‘The brain will monitor the situation and your sleep will be lighter and more likely to be disturbed.’