Basking in the blue glow of iPads, smartphones and other electronic devices before bedtime could be messing up our sleep patterns more profoundly than we realize, and even affecting our long-term health, according to a new study published Monday in the Proceedings of the National Academy of Sciences. 
 
 "It may be having a greater impact than we previously thought," said Anne-Marie Chang, a professor at Penn State University and a co-author of the study, which was conducted at Brigham and Women's Hospital in Boston. 
 
 A growing body of evidence has suggested what many people have experienced firsthand - that the pervasive glow of electronic gadgets can hinder a good night's sleep. But researchers behind Monday's study, which was supported by a grant from the National Institutes of Health, set out to decipher what changes in the body cause those disruptions. 
 
 During a two-week inpatient experiment involving a dozen adults, some participants were asked to read on an iPad for four hours each night before bedtime, for five consecutive nights. Others read printed books in dim light. After a week, the groups switched. 
 
 Researchers found that participants using iPads displayed reduced levels of melatonin, a hormone that typically increases in the evening and helps induce sleepiness. They took longer to fall asleep, and spent less time in restorative REM, or rapid-eye movement, sleep. 
 
 In addition, the iPad readers reported being sleepier and less alert the following morning, even after eight hours of sleep. They also displayed delayed circadian rhythms. 
 
 "There's a lot of skepticism out there; a lot of people think this is psychological," said Charles Czeisler, director of the Division of Sleep Medicine at Harvard Medical School. "But what we showed is that reading from light-emitting, e-reader devices has profound biological effects." 
 
 Czeisler said that although the study used only iPads, the effect isn't unique to that device. Other products produce similar blue-light emissions, including tablets, e-readers, smartphones, laptops and LED monitors. Czeisler said the standard Kindle e-reader, which doesn't emit light, was an exception and was more akin to a printed book. (The Kindle is produced by Amazon; its chief executive, Jeff Bezos, owns the Post). 
 
 So other than a little grogginess, why should we worry about the apparent loss of sleep that our glowing screens are causing us? 
 
 Czeisler and Chang said that as electronic devices become only more prevalent, and as their use becomes more ubiquitous, their role in significant sleep loss could lead to long-term health consequences. For instance, chronic suppression of melatonin has been linked to increased risk of prostate, colorectal and breast cancers. And a persistent lack of sleep has been associated with obesity and diabetes. 
 
 "We introduce these devices that have medical and biological effects without requiring any health studies on their impact ... They don't have to go through any evaluation like a drug would, for safety and efficacy," Czeisler said. "I think it's time to rethink that." 
 
 A poll released earlier this year by the National Sleep Foundation offered a glimpse at just how pervasive electronics have become in American bedrooms. Nearly 90 percent of adults and 75 percent of children reported having at least one electronic device in their bedrooms, and many reporting having multiple devices, such as televisions, laptops and tablets. 
 
 The sleep-disrupting effects of such devices might be even more significant for older teens, ages 15 to 17, almost all of whom reported having electronic devices in their bedrooms and were far more likely to use them at night than younger children, even when an early school morning loomed. ||||| Image copyright Thinkstock 
 
 Even low levels of light in bedrooms may stop breast cancer drugs from working, US researchers have warned. 
 
 Animal tests showed light, equivalent to that from street lamps, could lead to tumours becoming resistant to the widely used drug Tamoxifen. 
 
 The study, published in the journal Cancer Research, showed the light affected sleep hormones, which in turn altered cancer cell function. 
 
 UK experts said it was an intriguing finding, but not proven in people. 
 
 Tamoxifen has transformed the treatment of breast cancer by extending lives and increasing survival times. 
 
 It stops the female hormone oestrogen fuelling the growth of tumours although the cancerous cells may eventually become resistant to the drug. 
 
 Light 
 
 Researchers at the Tulane University School of Medicine investigated the role of the body clock in Tamoxifen resistance. 
 
 They focused their research on the sleep-promoting hormone melatonin, which normally begins to rise in the evening and continues through the night, before falling away as dawn approaches. 
 
 However, light in the evening - such as from a smartphone, tablet or artificial lights - can lower melatonin levels. 
 
 Rats, with human breast cancer and treated with Tamoxifen, were left to sleep in a completely dark cage or one that had dim light. 
 
 The scientists showed that in dim light, melatonin levels were lower, the tumours were bigger and were resistant to Tamoxifen. 
 
 A second set of tests showed that giving those mice melatonin supplements kept Tamoxifen working and resulted in smaller tumours. 
 
 Image copyright Thinkstock 
 
 Dr Steven Hill told the BBC News website: "I'm not advocating people buy melatonin over the counter, there's not enough evidence. 
 
 "But they could make sure they sleep in a room that is completely dark or they could wear eye-masks to let night-time melatonin rise and take Tamoxifen right before going to bed, that would be the easiest way to see if it works." 
 
 Some studies have suggested that melatonin may improve cancer treatments. 
 
 It has been suggested that the hormone calms down cancer cells, which are working on overdrive, to slow down the processes needed to develop resistance. 
 
 Dr Hill wants to move the research into human breast tissue. 
 
 Evening tech 
 
 He did add a warning about using technology, which tends to produce blue light wavelengths that disrupt melatonin production, in the run-up to bedtime. 
 
 "If you get seven hours sleep at night, but use an iPad or computer or watch TV then those blue wavelengths are suppressing melatonin production for anywhere from an hour to an hour and half. 
 
 "So instead of seven hours of melatonin, you're getting six or five and a half." 
 
 Dr Samuel Godfrey, from the charity Cancer Research UK, said: "The link between developing drug-resistant breast cancer and sleeping in dim light is an intriguing one, but it's important that we remember this link was found after studying a small number of rats implanted with breast cancer cells, not humans. 
 
 "More research in people is needed before we know whether the same mechanisms are at work in people." ||||| Image copyright Getty Images Image caption Correlations between screen time and lack of sleep are "extremely modest", says the report 
 
 The amount of time children spend on devices has little effect on how long they sleep, a study from Oxford University suggests. 
 
 It runs counter to previous research that suggested excessive screen time was linked to children failing to get sufficient rest. 
 
 The survey concluded that the relationship between sleep and screen use in children was "extremely modest". 
 
 But one UK GP said the findings did not tally with his clinical experience. 
 
 The study, conducted by the Oxford Internet Institute, relied on data from a 2016 US study into children's health, in which parents from across the country completed surveys about their households. 
 
 The children's "digital screen time" was based on answers to two questions about the weekday habits of children aged between six months and 17 years: 
 
 how much time they spent on computers, mobile phones, handheld video games and other electronic devices 
 
 how much time they spent in front of a TV watching programmes and other content as well as playing video games 
 
 The findings indicate that the tech-abstaining teenagers slept only slightly longer than their counterparts who had spent much of their day in front of a screen. 
 
 For example, teenagers who had not been in front of a screen for any part of the day got a total of eight hours and 51 minutes of sleep. 
 
 Those who had spent eight hours of their day glued to a screen got eight hours and 21 minutes of slumber. 
 
 The sample size for the survey was more than 50,000 youngsters from every state in the US. 
 
 'Mini case of jet lag' 
 
 The study, published in the Journal of Pediatrics, said every hour of screen time was linked to between three to eight fewer minutes of sleep a night. 
 
 Screens are now a fixture of modern childhood and both professionals and parents are increasingly expressing concerns that the amount of time children devote to devices affects their physical and mental health. 
 
 When it comes to sleep, there are concerns that children take devices to bed and continue to use them when they should be sleeping. 
 
 Others have expressed worries about the role the blue light emitted from such devices plays on sleep habits and a related hormone. 
 
 The US National Sleep Foundation has told parents that it is important to stop children using electronic devices before bedtime "because the blue light emitted from these screens can delay the release of sleep-inducing melatonin". 
 
 "This is an especially big problem for teens whose circadian rhythms are already shifting naturally, causing them to feel awake later at night. The end result: sleep-deprived or poorly rested kids who have essentially given themselves a mini case of jet lag," it writes on its website. 
 
 'Imperfect data' 
 
 But the study author thinks other factors should be considered. 
 
 "Focusing on bedtime routines and regular patterns of sleep, such as consistent wake-up times, are much more effective strategies for helping young people sleep than thinking screens themselves play a significant role," said study author Prof Andrew Przbylski. 
 
 Prof Przbylski told the BBC that many of the studies suggesting links between screen time and lack of sleep had very small sample sizes and need "much larger studies" to find conclusive evidence of a problem. 
 
 "Because the effects of screens are so modest, it is possible that many studies with smaller sample sizes could be false positives - results that support an effect that in reality does not exist," he said. 
 
 He acknowledged that the data used in the study was "imperfect" because it relied on reports from parents. A further study into the time that children turn off their devices before bedtime will be published shortly. 
 
 Many of the large technology firms, including Apple, Google and Facebook, have introduced dashboards allowing people to keep a check on the amount of time they spend on screens. 
 
 Some leading technology executives have banned their own children from using devices. 
 
 The late Apple chief Steve Jobs's young children were notably not allowed iPads. 
 
 Microsoft co-founder Bill Gates banned phones until his children were teenagers. 
 
 And Tim Cook, Apple's current leader, has said he would not let his nephew join social networks. 
 
 One UK GP, Rangan Chatterjee, said the Oxford University study was "welcome" but that he did not plan to change his advice to parents, which was to turn off devices an hour before bedtime. 
 
 "The more research on this area, the better because screens are here to stay," he told the BBC. 
 
 "But the findings don't replicate what I see in clinical practice which is that the use of screens right before bed has a significant impact on the quality of sleep."
– Your iPad or smartphone could well be hurting your sleep patterns, even if you're getting in a full eight hours of shuteye, researchers say—and the effects could be long-term. Over a five-night period, researchers in Boston had some subjects read for four hours a night on an iPad; others did their reading on printed books, with the lights low, the Washington Post reports. Among members of the iPad group, levels of melatonin, a chemical behind sleepiness, decreased. It took them longer to drift off by an average of 10 minutes, the Wall Street Journal reports. And once they did, their periods of rapid eye-movement sleep were shorter. The effects weren't limited to the nighttime. Their circadian rhythms were affected, and the next day—even if they'd slept eight hours—they reported being more tired. And in the long term, reduced melatonin may boost the risk of various forms of cancer (prompting the rather frightening headline "Reading an iPad in Bed May Increase Cancer Risk," the Atlantic notes). At issue is what's known as "blue light," the kind often given off by backlit gadgets, the Journal adds. "We introduce these devices that have medical and biological effects without requiring any health studies on their impact ... They don't have to go through any evaluation like a drug would, for safety and efficacy," says a researcher. "I think it's time to rethink that." (As far as sleep goes, here's your "optimal" amount.)