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. ||||| The bed must be reserved as a place for sleep and sex only. That was the decree of psychologist Richard Bootzin in his influential 1972 proposal for a "stimulus-control" approach to better sleep. One central tenet was operant conditioning: The bed must be a sanctuary, such that the brain is trained to sleep when it is in the bed. The allowance for sex—which, in its ideal form, is one of the most stimulating things a human body can experience—always seemed to me at odds with the stimulus-control approach. A note to aspiring self-help writers: The book For Better Sleep, Kitchen Sex remains unwritten. Otherwise, though, the idea of stimulus control made sense to a lot of people. It also included advice to avoid bedroom behaviors that abet anxiety, like clock-watching. And Bootzin's approach to insomnia endured, proving itself in several studies. So last year when Charles Czeisler, a professor of sleep medicine at Harvard Medical School, found that around 90 percent of Americans use some kind of electronic device within the hour before bed—and correlated the degree of use with ever-poorer sleep—one of his first theories of the case was overstimulation. That's because, Czeisler and colleagues wrote in the Journal of Clinical Sleep Medicine in December of 2013, "In addition to making phone calls, cell phones now allow the user to instant message, listen to music, send emails, play games, and surf the Internet." So they do. And all of that stimulation, the researchers proposed, may "impede the natural withdrawal of sympathetic nervous system activity necessary for sleep onset." Or, preclude one's ability to chill. To what degree is the light from a device, not the cognitive stimulation it provides, responsible for the known sleep effects of screens? A more vague hypothesis raised by Czeisler at the time was that the detrimental effects on sleep might be due to "light and electromagnetic transmissions from technological devices." Other researchers, too, have lately blamed the light exposure element, which is well understood to influence sleep patterns through photoreceptors in the retina that tell the brain to release the hormone melatonin. It flows forth from the pineal gland into the blood and around the body. Normally, melatonin levels rise before bedtime, peak in the middle of the night, and decrease in the early morning. That is why daily light-dark cycles are important for normal levels of alertness and sleep in most people. Abnormalities in these cycles are the basis for shift-work sleep disorder. But to what degree is the light from a device, not the cognitive stimulation it provides, responsible for the known sleep effects of screens? And is that light worse than, say, the light from a light bulb? In research published today in the journal Proceedings of the National Academy of Sciences, Czeisler and colleagues made an interesting advance in understanding that idea, and just how screens themselves tell our brains to stay awake. It began with the mundane observation that people read to unwind—often at night, often in bed. As far as sleep is concerned, Czeisler wondered, does it matter whether those people read books on iPads, Kindles, or paper? 
 
 Czeisler and colleagues, including lead researcher Anne-Marie Chang, an associate neuroscientist in the division of sleep medicine at Harvard Medical School, recruited a small group of people for an intensive experiment. For two weeks, participants took up residence in a monitoring unit at the clinical investigation center at Boston's Brigham and Women's Hospital. The subject group was only 12 people, but for a trial that requires so much commitment, that is not an unimpressive number. Though it was an enviable situation, in some ways: The people were allotted an idyllic eight hours for sleep, from 10:00 p.m. to 6:00 a.m.—a schedule they kept for three weeks prior, as well, in preparation. They were also allotted four hours of undisturbed reading time each night. The elements of a changing world, from technology and business to politics and culture. 
 
 Read More For five days in a row, the people read either a book or an iPad for four hours prior to sleep. Both were kept at constant, preordained distances from the person's face. Chang and colleagues monitored the people's sleep patterns with electroencephalograms all night. Each person did one stint with the iPad, and one with the book. Before and after each trial period, the people underwent hourly blood tests to paint a day-long picture of just how much melatonin was in their veins at any given time. When subjects read on the iPad as compared to the paper books (hereafter referred to as "books"), the people reported feeling less sleepy at night and less alert the following morning. Of course, this is not a blinded study, the kind with a placebo—the participants could have been biased in reporting how they felt. But, empirically, they also took longer to fall asleep on the iPad nights and spent less time in the REM phase of sleep. And the blood tests showed that on average, the brain's melatonin secretion on those nights was delayed by an hour and a half. Though this experiment dealt exclusively with iPads, the researchers also tested the light-emission patterns of other tablets, as well as phones and laptops. Chang told me they all emitted similar patterns, enriched for short-wavelength blue light, and at a similar intensity. So she would expect similar clinical findings for any such device. ||||| The modern bedroom is full of lights, from glowing computer monitors and clock radios to any number of blinking and glimmering electronic devices. Trouble is, chronic exposure to light at night leads to a host of health problems. 
 
 To understand why chronic exposure to light at night is so bad, we need to consider human evolution. Prior to the end of the stone age, humans were exposed to two different kinds of natural light responsible for regulating circadian rhythmicity. During the day we had the sun, while at night we had the moon and the stars, and perhaps the light from campfires. The binary day/night pattern was unrelenting, and our biological programming followed suit. 
 
 Today, we have artificial lighting at night (LAN), and it's a different case altogether. Indoor lighting is considerably less powerful than sunlight, but many orders of magnitude greater than star and moonlight. Check out this chart to see what I mean: 
 
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 Keep in mind that this is a logarithmic scale, so the difference between sunlight and moonlight is considerable — a difference that influences a series of critical biochemical cascades tied to light periodicity, including the production of cortisol and melatonin levels. 
 
 Light is a Drug 
 
 Melatonin suppression is key to understanding much of why LAN is so crappy for us. This workhorse biochemical is produced by the brain's pineal gland at night — when it's dark — to regulate our sleep-wake cycle. It lowers blood pressure, glucose levels, and body temperature — key physiological responses responsible for restful sleep. As neurologist George Brainard puts it, "Light works as if it's a drug, except it's not a drug at all." 
 
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 The part of your brain that controls your biological clock is the Suprachiasmatic Nucleus (SCN), a group of cells in the hypothalamus. These cells respond to light and dark signals. The optic nerves in our eyes senses light and transmits a signal to the SCN telling the brain that it's time to wake up. It also kickstarts other processes, like raising body temperature and producing hormones like cortisol. Our cortisol levels are relatively low at night, allowing us to sleep, and higher during the day, allowing for the stabilization of energy levels and the modulation of immune function. 
 
 But LAN unnaturally elevates cortisol levels at night, which disrupts sleep and introduces a host of problems relating to body-fat levels, insulin resistance, and systemic inflammation. It also contributes to sleep debt and a disruption the neuroregulation of appetite. 
 
 But if our rooms are dark at night, there's no optic signal to the SCN, so our bodies pump out the much needed melatonin. Moreover, our melatonin levels are regulated according to the amount of exposure we had to light during the previous day. 
 
 Related: The science behind power naps and insomnia. 
 
 The Light Before You Sleep 
 
 Indeed, studies have shown that exposure to room light before bedtime shortens melatonin duration by about 90 minutes compared to dim light exposure. In addition, exposure to room light during usual hours of sleep suppresses melatonin levels by more than 50%. That's significant. 
 
 So, even before you hit the hay, the light in your bedroom is causing you problems. With the introduction of tablets, smartphones, and energy-efficient light bulbs, it's an issue that's only getting worse. 
 
 And just to add insult to injury, many modern devices emit blue light from light-emitting diodes (LEDs) — light that's especially good at suppressing melatonin. This is because melanopsin — a photopigment found in specialized cells of the retina involved in the regulation of circadian rhythms — is most sensitive to blue light. 
 
 Recently, scientists warned college students about the impact of light from computer monitors on melatonin levels. They found that computer light at night — particularly blue light that was scanned by wearing different wavelength-blocking glasses — reduces college students' melatonin levels. A related study found that backlit tablet displays suppress melatonin, disrupting sleep. But the researchers write: "[It] is important to acknowledge that usage of self-luminous electronic devices before sleep may disrupt sleep even if melatonin is not suppressed. Clearly, the tasks themselves may be alerting or stressful stimuli that can lead to sleep disruption." Which is a very good point. 
 
 The Cancer Link 
 
 Regrettably, all this hormone and biochemical disruption is creating downstream effects — cancer being one of them. Scientists aren't entirely sure why, but studies consistently show a correlation. 
 
 For example, a 10-year study found that a sample group of over 1,670 women exposed to higher intensity light in their sleeping environment had 22% higher odds of developing breast cancer than those who slept in total darkness. The researchers blamed it on hormone disruption caused by melatonin suppression. 
 
 In another study, researchers implanted nude rats with breast cancer xenografts and then gave them perfusions of blood from different women. Rats receiving blood from women who were exposed to dim light at night had their tumor growth reduced — but those with blood from women who were exposed to bright light at night weren't granted this beneficial effect. 
 
 Troublingly, this has grim implications for workers who do shift work. Case-controlled studies have shown that nurses who work rotating shifts at midnight are more at risk for breast cancer compared to nurses with permanent day work. 
 
 Low Light, Blue Light, Depression and Immune Response 
 
 Disturbingly, the light at night doesn't even have to be bright to cause problems. Chronic exposure to dim light at night leads to depression-like symptom in hamsters, such as exhibiting less interest in drinking the sugar water that they normally love. But by returning them to a normal, non-lit day/night schedule, the researchers were able to reverse the depression. Scientists suspect that this dim-light depression may be the result of a protein called tumor necrosis factor. 
 
 Chronic dim light at night also detrimentally affects the immune system. 
 
 You might want to think about this next time you leave even the dimmest lights on in your bedroom — including your clock radio and the light that bleeds in from street lights. 
 
 Another study, also on rodents, showed that blue light at night in particular is especially powerful at inducing depression-like symptoms. LAN can also impair mood and learning, again likely on account of melanopsin-expressing neurons. 
 
 Premature Aging and Heart Problems 
 
 Melatonin also has antioxidant properties, which plays an important role in anti-aging. Researchers have been able to treat artificially aged mice with melatonin, thus reducing oxidative stress. These mice models are helping scientists understand the fundamental mechanism behind aging because they're the same markers found in neurodegenerative diseases like Alzheimer's. 
 
 Other studies show a link between melatonin suppression and cardiovascular disease. 
 
 Weight Gain 
 
 Light at night also contributes to weight gain by shifting the time of our food intake. Mice, when exposed to LAN, gained more weight — despite exercising and eating as much as their darkness-exposed brethren. Scientists have also correlated low levels of melatonin to diabetes, though it's not clear what role, if any, LAN plays in this matter. 
 
 Pitch Black 
 
 All this research points to one basic fact: We need to keep our bedrooms as dark as possible and avoid blue light before sleep. To that end, you should turn off all your light-emitting gadgets and close the blinds. And if possible, refrain from reading your tablet computer or smartphone in the hours preceding sleep. 
 
 I know, easier said than done. 
 
 Additional reporting by Joseph Bennington-Castro. 
 
 Images: Africa Studio/Shutterstock, MNStudio/Shutterstock. 
 
 Follow me on Twitter: @dvorsky
– 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.)