Most people who own iPhones use them as their alarm clock — making it all too easy to check email one last time before falling asleep and hard to ever feel unplugged from work and social networks.

Several years ago my boss, Arianna Huffington, passed out from exhaustion after staying up late to catch up on work. She banged her head on the way down and ended up with five stitches — and became what she calls a "sleep evangelist." Now she leaves her phone charging in another room when she goes to bed and encourages friends to do the same.

"I sent all my friends the same Christmas gift — a Pottery Barn alarm clock — so they could stop using the excuse that they needed their very tempting iPhone by their bed to wake them up in the morning," she said.

If your phone wakes you up in the morning, it may also be keeping you up at night. A 2008 study funded by major mobile phone makers themselves showed that people exposed to mobile radiation took longer to fall asleep and spent less time in deep sleep.

"The study indicates that during laboratory exposure to 884 MHz wireless signals components of sleep believed to be important for recovery from daily wear and tear are adversely affected," the study concluded.

And that's just a physical symptom of sleeping near the phone — "sham" exposure to a phone without radiation failed to produce the same effect. The itch to check in at all hours of the night or wake up to the sound of a text message disrupts our sleep, too. A quarter of young people feel like they must be available by phone around the clock, according to a Swedish study that linked heavy cell phone use to sleeping problems, stress and depression. Unreturned messages carry more guilt when the technology to address them lies at our fingertips. Some teens even return text messages while they are asleep.

Most of us choose not to set limits on our nighttime availability. Nearly three-quarters of people from the age of 18 to 44 sleep with their phones within reach, according to a 2012 Time/Qualcomm poll. That number falls off slightly in middle age, but only in people 65 and older is leaving the phone in another room as common as sleeping right next it.

This story appears in Issue 42 of our weekly iPad magazine, Huffington, in the iTunes App store, available Friday, March 29.

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  • You're Ravenous

    If you find yourself hungry all day (and not because you skipped breakfast or have recently amped up your gym routine) it might be because you've been skimping on sleep. Research presented at the 2010 meeting of the Society for the Study of Ingestive Behavior linked little shuteye with <a href="http://www.huffingtonpost.com/2012/07/10/sleep-hunger-deprivation-_n_1659954.html">higher levels of the hormone ghrelin</a>, the same one that triggers hunger, HuffPost reported. This uptick in the hunger hormone seems to lead to not only increased snacking, but also a hankering for <a href="http://www.sciencedaily.com/releases/2004/12/041206210355.htm">high-carb, high-calorie foods</a>, according to a 2004 study, which may help explain why people who don't get enough sleep are at a greater risk of obesity.

  • You're Weepy

    Ever find yourself tearing up over an embarrassing TV commercial? While women might be quick to blame PMS, it could be a lack of sleep sending your emotions into overdrive. A 2007 study found that sleep-deprived brains were <a href="http://usatoday30.usatoday.com/news/health/2007-10-22-sleep-deprivation-brain_N.htm">60 percent more reactive</a> to negative and disturbing images, <em>USA Today</em> reported. "It's almost as though, without sleep, the brain had reverted back to more primitive patterns of activity, in that it was <a href="http://berkeley.edu/news/media/releases/2007/10/22_sleeploss.shtml">unable to put emotional experiences into context</a> and produce controlled, appropriate responses," Matthew Walker, senior author of the study, said in a statement.

  • You're Forgetful Or Unfocused

    You might be tempted to blame your trouble focusing on your age or stress or your overflowing email inbox, but a lack of sleep could be the true culprit. Too few hours in dreamland has been linked to a <a href="http://www.webmd.com/sleep-disorders/excessive-sleepiness-10/emotions-cognitive">whole host of cognitive problems</a>, like difficulty focusing and paying attention, confusion, lower alertness and concentration, forgetfulness and trouble learning, WebMD reports. So next time you find yourself forgetting where you put your keys, consider how much sleep you got last night.

  • You Can't Shake That Cold

    If you keep coming down with the sniffles -- or can't seem to kick that never-ending case -- you might want to assess your sleep schedule. A 2009 study found that people who sleep fewer than seven hours each night have almost <a href="http://articles.latimes.com/2009/jan/17/science/sci-sleep17">three times the risk of catching a cold</a> than people who slept for at least eight hours, the <em>LA Times</em> reported.

  • You're Clumsier Than Usual

    First you knock the alarm clock off the dresser, then you spill the milk as you're pouring your cereal, then you stub your toe on the way out the door -- you've become a klutz overnight. Researchers don't know exactly why, but sleepy people seem to <a href="http://www.prevention.com/amisleepdeprived/list/5.shtml">"have slower and less precise motor skills,"</a> Clete Kushida, M.D., Ph.D., director of Stanford University Center for Human Sleep Research told <em>Prevention</em>. Reflexes are dulled, balance and depth perception can be a little wonky and since you may also have trouble focusing, reaction time can be slowed, meaning you can't quite catch the egg carton before it hits the floor.

  • You've Lost That Lovin' Feeling

    If you or your partner just can't get in the mood, and stress or an underlying health problem isn't to blame, you might want to spend some extra time between the sheets -- sleeping. Both men and women who don't get their 40 winks experience a <a href="http://www.webmd.com/sleep-disorders/excessive-sleepiness-10/10-results-sleep-loss">decreased sex drive</a> and less interest in doing the deed, WebMD reports. A lack of sleep can also <a href="http://www.everydayhealth.com/erectile-dysfunction/causes-of-low-libido.aspx">elevate levels of cortisol</a>, the stress hormone, according to Everyday Health, which doesn't help in the bedroom either.

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