<p>Our being accessible all the time may not be as great as we think it is. Photograph: Mark Bowden/Getty Images</p><p>More than 80% of people with smartphones have them switched on all the time, including in bed. Mobiles or tablets often get used as alarm clocks, but once on the bedside table they're a terrible temptation for one final text or email after the light goes out.</p><p>Four out of 10 adults say they use their smartphone if it wakes them. But even if your device doesn't go off it may disrupt your sleep. A small study of tablets (used by 13 volunteers aged 20) from the Rensselaer Polytechnic Institute in New York found that exposure to light from these sources suppresses the body's melatonin levels by 23% when used for two hours before bedtime. The authors speculated that since melatonin levels reflect how dark it is outside and tell the body how ready it should be for sleep, tablets may contribute to insomnia.</p><p>The Emory sleep disorders laboratory in America advises not using a tablet before bed, even just to read, because the light shines directly into your eyes if you read with a lamp, the light points down. Last week research from the Mayo Clinic in Arizona, published in the journal Sleep, suggested, not at all radically, that turning down the light on these devices could reduce melatonin suppression and improve sleepiness. So can you stack your mobile devices back on your bedside table after all?</p><p><a href="http://www.guardian.co.uk/lifeandstyle/2013/jun/09/smartphones-tablets-in-bedroom-sleep">Keep reading...</a></p>