circadian rhythms

Blue light may not affect your sleep-wake cycle, study finds

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Researchers say that blue light may not significantly affect a person’s circadian rhythms. AleksandarNakic/Getty Images

  • Blue light from the sun is vital in regulating a person’s sleep-wake cycle.
  • New research suggests that blue light does not affect a person’s “internal clock.”
  • The findings further our understanding of the effects of light on sleep quality and duration.
  • Previous studies have shown that blue light from devices can damage the eyes and negatively impact sleep.

Of the seven colors in the visible light spectrum, blue lightTrusted Source is the one most people know and talk about.

The majority of light coming from the sun is blue light, making it vital in helping to regulate a person’s sleep-wake cycle.

However, blue light is also the type of light emitted by computer screens, smartphones, tablets, and LED televisions.

Previous research shows that too much exposure to blue light from technology devices can potentially damageTrusted Source the eye’s retina, lead to digital eyestrainTrusted Source, and negatively affect sleep quality and durationTrusted Source.

Now, a new study by researchers at the University of Basel in Switzerland suggests that blue light may not affect a person’s “internal clockTrusted Source.”

The study was recently published in the journal Nature Human BehaviourTrusted Source.

How does light affect circadian rhythm?

Ganglion cellsTrusted Source are a type of photoreceptor in the eye that plays a role in the sleep-wake cycle.

The other two photoreceptors in the eye — rods and cones — convert light coming into the eye into electrical signals relayed to the brain, providing vision.

First study author Dr. Christine Blume, a psychologist at the Centre for Chronobiology of the University of Basel in Switzerland, explained to Medical News Today:

“In humans, the main effect of light on the internal clock and sleep is mediated via specialized light-sensitive ganglion cells in the retina, which are maximally responsive to short-wavelength light around 490 nanometres. This was well-established even before our study. However, there was reason to believe that the color of light, which is encoded by the cones, could also be relevant for the internal clock, because also cone-signals serve as an additional input to the internal clock. The question was, whether this input is also relevant.”

Effects of blue light vs. yellow light on sleep

For this study, Dr. Blume and her team recruited 16 human participants who were exposed to a blueish light, a yellowish light, and a white control light for one hour before bedtime.

Researchers designed the lights in a way that they activated the color-sensitive cones in the retina in a controlled manner and the stimulation of the light-sensitive ganglion cells was the same in all three conditions. This allowed scientists a way to separate the light properties that might affect the sleep-wake cycle.

Dr. Blume said they decided to focus on blue and yellow light in this study as a study in 2019Trusted Source on mice found that yellowish light had a stronger effect on the mice’s rest-activity cycle than blueish light.

“The most striking changes in brightness and light color (i.e., changes from orange to blueish or vice versa) occur around sunrise and sunset, marking the beginning and end of a day,” Dr. Blume noted.

“Thus, especially changes along the blue-yellow dimension may be relevant for the internal biological clock.”

Variation in light color does not affect circadian rhythm

At the conclusion of the study, researchers reported they found no evidence that the variation in light color along the blue-yellow dimension played a relevant role in affecting human circadian rhythm.

“Rather, our results support the findings of many other studies that the light-sensitive ganglion cells are most important for the human internal clock,” Dr. Blume said.

The researchers still recommend people reduce their exposure to short-wavelength light emitted from smartphones and other technology devices — despite what color it may be — before going to sleep, as they can affect circadian rhythm.

“The problem is that in everyday language we often refer to the short-wavelength light to which the specialized ganglion cells are most sensitive as ‘blue light’,” Dr. Blume explained. “This is despite the fact that the light does not have to be perceived as blue.”

“Our results support the findings of many other studies that the light-sensitive ganglion cells are most important for the human internal clock,” she continued.

“Therefore, short-wavelength light — misleadingly often termed ‘blue light’ — should be reduced in the evening, for example by dimming computer screens and using a night-shift mode. Avoiding screen time before bed can also help, as the things we do on our phones often delay sleep.”

Many factors affect the body’s ‘internal clock’

After reviewing this study, Dr. Benjamin Bert, an ophthalmologist at MemorialCare Orange Coast Medical Center in Fountain Valley, CA, told MNT that this study was interesting as it tried to show that while light color may not make a difference to a person’s sleep-wake cycle, other aspects that could.

“They talked about low melanopic lightTrusted Source, which still is trying to get rid of the short wavelength light, in order to allow for an easier time of going to sleep,” Dr. Bert continued.

“But I think what we’re really seeing is that it’s so multifactorial that trying to figure out one specific thing that could be contributing to these issues or these concerns needs a lot of research to flush it out.”

MNT also spoke with Dr. Alexander Solomon, a surgical neuro-ophthalmologist and strabismus surgeon at Pacific Neuroscience Institute at Providence Saint John’s Health Center in Santa Monica, CA, who said the modulation of a person’s internal circadian rhythm is rather complex.

“There is a master ‘clock’ set by melanopsin cellsTrusted Source — which are still most sensitive to blue light — but other activities such as meal timing and exercise can feed back to that master clock as well,” Dr. Solomon added.

Decreasing light exposure before bed may improve sleep

Dr. Solomon said if a person is having difficulty sleeping and waking at a regular time needed for their lifestyle, one change could be to use blue light-blocking glasses or a similar phone or screen setting, but also to decrease overall exposure to bright light.

“Quite frankly, as shown by this study, a bright enough yellow light or medium brightness normal lighting is equivalent to a dim blue light after a certain time,” Dr. Solomon explained.

“There can be many other factors that play a role in difficulty sleeping, and seeing a sleep specialist/hygienist may be helpful before attributing it to a single factor such as light exposure,” he added.

Dr. Bert agreed: “Usually when we’re looking at something, we’re also activating the brain, which makes it harder for us to kind of calm down and be able to easily go to sleep.”

“It would still be a good practice to take a break from anything that is projecting light into your eyes a few hours before trying to go to sleep and just give yourself some time to relax and let your brain calm down as well to ease you into sleep.”

— Dr. Benjamin Bert, ophthalmologist

Your Body’s Witching Hours .

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Circadian rhythms help determine when we are most vulnerable to disease

Researchers are finding that the body’s internal clocks can play a role in determining when some diseases may flare up. WSJ’s Melinda Beck reports.

Heart attacks often occur in the morning. Epileptic seizures peak in the late afternoon. Asthma attacks get worse and more deadly between 11 p.m. and 3 a.m.

Researchers are finding that circadian rhythms, which cycle every 24 hours or so, drive virtually every system in the human body, from circulation and cognition to metabolism, memory and mood. And they play a big role in determining when we are most vulnerable to disease.

Chronobiology—the study of these internal clock mechanisms—has exploded in recent years thanks in part to the discovery of specific genes, to which scientists have given names like Clock, Period and Cryptochrome. Those genes help keep our biological systems in sync with light and darkness, which makes for a rush hour of chemical changes at dawn and dusk.

Understanding biorhythms is helping doctors direct treatments, including the best times to take various medications. It is also suggesting new treatment strategies, such as adjusting the light in nursing homes to help people sleep better.

Of course, people often disrupt their circadian cycles with jet travel, erratic work schedules, watching TV and Web surfing long into the night. That can raise the risk for a variety of health problems, including heart disease and diabetes.

The body’s master time keeper is a group of neurons in the hypothalamus, located behind the eyes, called the suprachiasmatic nucleus, or SCN. In darkness, the SCN prompts the pineal gland to release melatonin, the hormone that facilitates sleep. Other chemical changes reduce body temperature, blood pressure and heart rate, all of which are at their lowest overnight.

ENLARGE
JASON SCHNEIDER

Other systems are highly active at night. Stomach-acid production peaks between 10 p.m. and 2 a.m., digesting the evening meal and possibly exacerbating heartburn. The liver dumps glucose into the bloodstream just before dawn. Leptin, a hormone that damps appetite, is high, so people tend to be least hungry when they wake up. And the immune system may be overactive, inflaming airways in asthma sufferers and swelling arthritic joints.

In the morning, light on the retinas signals the SCN to shut off melatonin. Cortisol, a stress hormone, rises instead, preparing the body for the day’s demands. Blood pressure and heart rate start increasing. A substance called PAI-1, which makes blood clot more readily, peaks around 6:30 a.m. Experts think PAI-1 may have protected early humans from bleeding to death from an injury as they set off foraging for food. But in modern humans with plaque-lined arteries, the substance raises the risk of blockages that cause heart attacks and strokes. Those peak around 9 a.m., studies show.

Exposure to bright light at a time the body isn’t used to can advance or delay the circadian cycle. But that doesn’t happen right away, as jet-lag sufferers know. An earlier study that lasted 11 years found that heart attacks among vacationers in Hawaii corresponded more closely to early morning back home than they did to local time.

Eating, sleeping and other behavioral patterns, of course, also affect the body’s daily changes. But various biological systems, including blood pressure, heart rate, blood clotting and adrenaline, rise and fall in circadian rhythms of their own, according to research at the Medical Chronobiology Program at Brigham and Women’s Hospital in Boston and at other centers. If those behavioral patterns and circadian rhythms get out of sync, a variety of health problems can result, as researchers have shown in experiments with lab animals and observed in humans.

For example, when rodents are fed during their usual sleep time, their liver and pancreas adjust to that feeding schedule but their SCN master clock doesn’t. Even if the amount of food is the same, they will gain more weight and fat than rodents fed at the normal time, says Frank Scheer, the chronobiology program’s director.

ENLARGE

Shift workers—who make up about 10% of the U.S. workforce—are vulnerable to similar problems when they eat, sleep and work out of sync with their circadian rhythms. Many have higher rates of heart disease, diabetes, obesity, high blood pressure, stroke and other disorders.

Millions of other people develop what experts call “social jet lag” by staying up late and sleeping late a few days each week. “If you do that Friday, Saturday and Sunday, then by Monday morning, when you have to go to work, you are waking up at a much earlier circadian time, which can have consequences for days to come,” says Dr. Scheer. Even theone-hour shift that occurs with setting clocks forward in the spring raises the rate of heart attacks for a week, studies show.

Surveys of tens of thousands of adults by the University of Munich’s Institute of Medical Psychology have found that the greater the difference between sleep time on weekdays and weekends, the more likely people are to be obese.

Many people with depression, bipolar disorder and other mental-health issues have disrupted circadian rhythms and erratic sleep patterns. Patients with bipolar disorder tend to have cycles that are longer than 24 hours, says psychiatrist Michael McCarthy, a member of the University of California, San Diego’s Center for Circadian Biology. There is growing evidence that these problems may be related to defects in clock genes.

Sleep cycles become earlier, shorter and more fragmented as people age. “The studies all show that having disrupted circadian rhythms puts older people at greater risk for cognitive impairment, depression and mortality,” says Sonia Ancoli-Israel, a professor emeritus of psychiatry at the UCSD center.

Such issues are even more pronounced in people with Alzheimer’s disease, whose sleep, core temperature and other biorhythms don’t follow predictable patterns. The increased restlessness, irritability and confusion known as “sundowning” that some Alzheimer’s patients experience in late afternoon isn’t well understood. Another mystery is the so-called witching hour surge in crankiness that babies often demonstrate at the end of the day.

“At the extremes of life, in babies where the brain hasn’t fully developed or in dementia patients, when you are getting degeneration, the time connections in the brain may not be fully coordinated,” Dr. McCarthy suggests. “And fatigue makes everything worse.”

Researchers are starting to develop treatment strategies to take advantage of circadian rhythms or restore them when they are out of sync—a field called chronotherapy.

“It’s a very promising area but the field is very young. More clinical trials need to be done,” says Steven Shea, a professor of public health and preventive medicine at Oregon Health and Science University.

Taking medications at night that help prevent heart blockages, such as long-acting beta-blockers and ACE inhibitors, may lower the risk of early morning heart attacks, experts say. Taking acid-blocking drugs at night might be more effective, given the overnight surge of stomach acid.

Light therapy has been shown to be effective at improving sleep among older people in nursing homes, according to several randomized, controlled trials. “Many older adults are not getting sufficient sunlight,” says Dr. Ancoli-Israel, of UCSD. She says nursing-home patients typically get only a few minutes of bright sunlight a day.

Administering melatonin to aid sleep also has been studied, but with mixed results. And melatonin can worsen glucose tolerance, so it isn’t useful for everybody.

In general, experts say going to bed, getting up and eating meals at the same time every day, getting lots of light in the morning and avoiding it at night can go a long way to improve health and mood. “It’s the same advice we’ve always given,” says Dr. McCarthy. “But now we understand a lot more about why that’s true.”

Researchers are finding that the body’s internal clocks can play a role in determining when some diseases may flare up. WSJ’s Melinda Beck reports. Photo: iStock/dashek
Heart attacks often occur in the morning. Epileptic seizures peak in the late afternoon. Asthma attacks get worse and more deadly between 11 p.m. and 3 a.m.

Researchers are finding that circadian rhythms, which cycle every 24 hours or so, drive virtually every system in the human body, from circulation and cognition to metabolism, memory and mood. And they play a big role in determining when we are most vulnerable to disease.

Chronobiology—the study of these internal clock mechanisms—has exploded in recent years thanks in part to the discovery of specific genes, to which scientists have given names like Clock, Period and Cryptochrome. Those genes help keep our biological systems in sync with light and darkness, which makes for a rush hour of chemical changes at dawn and dusk.

Understanding biorhythms is helping doctors direct treatments, including the best times to take various medications. It is also suggesting new treatment strategies, such as adjusting the light in nursing homes to help people sleep better.

Of course, people often disrupt their circadian cycles with jet travel, erratic work schedules, watching TV and Web surfing long into the night. That can raise the risk for a variety of health problems, including heart disease and diabetes.

The body’s master time keeper is a group of neurons in the hypothalamus, located behind the eyes, called the suprachiasmatic nucleus, or SCN. In darkness, the SCN prompts the pineal gland to release melatonin, the hormone that facilitates sleep. Other chemical changes reduce body temperature, blood pressure and heart rate, all of which are at their lowest overnight.

ENLARGE
JASON SCHNEIDER

Other systems are highly active at night. Stomach-acid production peaks between 10 p.m. and 2 a.m., digesting the evening meal and possibly exacerbating heartburn. The liver dumps glucose into the bloodstream just before dawn. Leptin, a hormone that damps appetite, is high, so people tend to be least hungry when they wake up. And the immune system may be overactive, inflaming airways in asthma sufferers and swelling arthritic joints.

In the morning, light on the retinas signals the SCN to shut off melatonin. Cortisol, a stress hormone, rises instead, preparing the body for the day’s demands. Blood pressure and heart rate start increasing. A substance called PAI-1, which makes blood clot more readily, peaks around 6:30 a.m. Experts think PAI-1 may have protected early humans from bleeding to death from an injury as they set off foraging for food. But in modern humans with plaque-lined arteries, the substance raises the risk of blockages that cause heart attacks and strokes. Those peak around 9 a.m., studies show.

Exposure to bright light at a time the body isn’t used to can advance or delay the circadian cycle. But that doesn’t happen right away, as jet-lag sufferers know. An earlier study that lasted 11 years found that heart attacks among vacationers in Hawaii corresponded more closely to early morning back home than they did to local time.

Eating, sleeping and other behavioral patterns, of course, also affect the body’s daily changes. But various biological systems, including blood pressure, heart rate, blood clotting and adrenaline, rise and fall in circadian rhythms of their own, according to research at the Medical Chronobiology Program at Brigham and Women’s Hospital in Boston and at other centers. If those behavioral patterns and circadian rhythms get out of sync, a variety of health problems can result, as researchers have shown in experiments with lab animals and observed in humans.

For example, when rodents are fed during their usual sleep time, their liver and pancreas adjust to that feeding schedule but their SCN master clock doesn’t. Even if the amount of food is the same, they will gain more weight and fat than rodents fed at the normal time, says Frank Scheer, the chronobiology program’s director.

ENLARGE

Shift workers—who make up about 10% of the U.S. workforce—are vulnerable to similar problems when they eat, sleep and work out of sync with their circadian rhythms. Many have higher rates of heart disease, diabetes, obesity, high blood pressure, stroke and other disorders.

Millions of other people develop what experts call “social jet lag” by staying up late and sleeping late a few days each week. “If you do that Friday, Saturday and Sunday, then by Monday morning, when you have to go to work, you are waking up at a much earlier circadian time, which can have consequences for days to come,” says Dr. Scheer. Even theone-hour shift that occurs with setting clocks forward in the spring raises the rate of heart attacks for a week, studies show.

Surveys of tens of thousands of adults by the University of Munich’s Institute of Medical Psychology have found that the greater the difference between sleep time on weekdays and weekends, the more likely people are to be obese.

Many people with depression, bipolar disorder and other mental-health issues have disrupted circadian rhythms and erratic sleep patterns. Patients with bipolar disorder tend to have cycles that are longer than 24 hours, says psychiatrist Michael McCarthy, a member of the University of California, San Diego’s Center for Circadian Biology. There is growing evidence that these problems may be related to defects in clock genes.

Sleep cycles become earlier, shorter and more fragmented as people age. “The studies all show that having disrupted circadian rhythms puts older people at greater risk for cognitive impairment, depression and mortality,” says Sonia Ancoli-Israel, a professor emeritus of psychiatry at the UCSD center.

Such issues are even more pronounced in people with Alzheimer’s disease, whose sleep, core temperature and other biorhythms don’t follow predictable patterns. The increased restlessness, irritability and confusion known as “sundowning” that some Alzheimer’s patients experience in late afternoon isn’t well understood. Another mystery is the so-called witching hour surge in crankiness that babies often demonstrate at the end of the day.

“At the extremes of life, in babies where the brain hasn’t fully developed or in dementia patients, when you are getting degeneration, the time connections in the brain may not be fully coordinated,” Dr. McCarthy suggests. “And fatigue makes everything worse.”

Researchers are starting to develop treatment strategies to take advantage of circadian rhythms or restore them when they are out of sync—a field called chronotherapy.

“It’s a very promising area but the field is very young. More clinical trials need to be done,” says Steven Shea, a professor of public health and preventive medicine at Oregon Health and Science University.

Taking medications at night that help prevent heart blockages, such as long-acting beta-blockers and ACE inhibitors, may lower the risk of early morning heart attacks, experts say. Taking acid-blocking drugs at night might be more effective, given the overnight surge of stomach acid.

Light therapy has been shown to be effective at improving sleep among older people in nursing homes, according to several randomized, controlled trials. “Many older adults are not getting sufficient sunlight,” says Dr. Ancoli-Israel, of UCSD. She says nursing-home patients typically get only a few minutes of bright sunlight a day.

Administering melatonin to aid sleep also has been studied, but with mixed results. And melatonin can worsen glucose tolerance, so it isn’t useful for everybody.

In general, experts say going to bed, getting up and eating meals at the same time every day, getting lots of light in the morning and avoiding it at night can go a long way to improve health and mood. “It’s the same advice we’ve always given,” says Dr. McCarthy. “But now we understand a lot more about why that’s true.”

Is Circadian Rhythm the Rhythm of Life?

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Pre-ovulatory hormone surge and ovulation may be controlled by novel circadian hiearchy.

Studies in rodents have revealed a novel circadian hierarchy critical for the coordination of pre-ovulatory luteinizing hormone (LH) surge and ovulation.

The research in hamsters and mice suggests that the suprachiasmatic nucleus (SCN) has dual roles in the regulation of ovulation, reported Lance Kriegsfeld, PhD, of the University of California Berkeley, and colleagues, published online April 14.

Circadian rhythms in mammals are generated by a brain clock located in the SCN of the anterior hypothalamus, and this research expands on earlier work examining how SCN communicates timing information throughout the body, they wrote inEndocrinology.

“Based on our findings, we propose that the SCN signals the kisspeptin and systems via direct neuronal projections to positively drive the LH surge,” the researchers wrote. “Concurrently, the SCN directly and perhaps more likely, indirectly, signals the RFamide-related peptide 3 (RFRP-3) system to coordinate the suppression of estradiol negative feedback with this positive drive.”

Circadian clock timing has been shown to be critical in mammalian reproduction, and evidence suggests that this timing is regulated by gonadotropins.

Research has shown that women with irregular work or sleep cycles can have reduced fertility and an increased chance for spontaneous abortions, Kriegsfeld’s group explained.

“The circadian system coordinates the timing of ovulation and sexual behavior to coincide with an individual’s species-specific temporal niche, with the pre-ovulatory LH surge occurring in the early morning in women and diurnal rodents and late afternoon in nocturnal rodents,” the researchers wrote. They added that in species with spontaneous ovulation, the timing of the LH surge is controlled by the master circadian pacemaker in the SCN of the anterior hypothalamus.

Estrogen negative feedback is responsible for restraining the GnRH neuronal system for most of the ovulatory cycle, but immediately before ovulation this feedback is removed to allow stimulation of the pre-ovulatory GnRH/LH surge by the circadian clock in SCN.

Kriegsfeld and colleagues examined the neurochemical pathway by which SCN controls RFRP-3 activity. They also attempted to determine if the RFRP-3 system exhibits time-dependent responsiveness to SCN signaling to time LH surge.

“We found that RFRP-3 cells in female Syrian hamsters (Mesocricetus auratus) receive close appositions from vasopressin (AVP)-ergic and SCN-derived vasoactive intestinal polypeptide (VIP)-ergic terminal fibers,” they wrote. “Central VIP administration markedly suppressed RFRP-3 cellular activity in the evening, but not the morning, relative to saline controls, whereas AVP was without effect at either time point. Double-label in situ hybridization (ISH) for Rfrp-3 and the VIP receptors VPAC1 and VPAC2, revealed that the majority of RFRP-3 cells do not co-express either receptor in Syrian hamsters or mice, suggesting that SCN VIP-ergic signaling inhibits RFRP-3 cells indirectly.”

The research showed that both the GnRH and RFRP-3 systems maintain their own circadian time to ensure the precise coordination of the “stimulation and disinhibition of the reproductive axis,” they noted.

“Given that epidemiological and experimental findings indicate a pronounced negative impact of circadian disruption on female reproductive health, systematically uncovering the mechanisms underlying the circadian control of the female reproductive axis has potential clinical implications,” they wrote.

E-Readers Foil Good Night’s Sleep

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Light-emitting electronic devices keep readers awake longer than old-fashioned print.

Use of a light-emitting electronic book (LE-eBook) in the hours before bedtime can adversely impact overall health, alertness and the circadian clock, which synchronizes the daily rhythm of sleep to external environmental time cues, according to Harvard Medical School researchers at Brigham and Women’s Hospital. These findings of the study that compared the biological effects of reading an LE-eBook to a printed book are published in the Proceedings of the National Academy of Sciences on December 22, 2014.

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“We found the body’s natural circadian rhythms were interrupted by the short-wavelength enriched light, otherwise known as blue light, from these electronic devices,” said Anne-Marie Chang, corresponding author and associate neuroscientist at Brigham and Women’s Division of Sleep and Circadian Disorders. “Participants reading an LE-eBook took longer to fall asleep and had reduced evening sleepiness, reduced melatonin secretion, later timing of their circadian clock and reduced next-morning alertness than when reading a printed book.”

Previous research has shown that blue light suppresses melatonin, impacts the circadian clock and increases alertness, but little was known about the effects of this popular technology on sleep. The use of light-emitting devices immediately before bedtime is a concern because of the extremely powerful effect that light has on the body’s natural sleep/wake pattern and how that may play a role in perpetuating sleep deficiency.

During the two-week inpatient study, twelve participants read digital books on an iPad for four hours before bedtime each night for five consecutive nights. This was repeated with printed books. The order was randomized with some reading on the iPad first and others reading the printed book first. Participants reading on the iPad took longer to fall asleep, were less sleepy in the evening and spent less time in REM sleep. They had reduced secretion of melatonin, a hormone that normally rises in the evening and plays a role in inducing sleepiness. Additionally, iPad readers had a delayed circadian rhythm, indicated by melatonin levels, of more than an hour. Participants who read on the iPad were less sleepy before bedtime but were sleepier and less alert the following morning after eight hours of sleep. Although iPads were used in this study, researchers also measured other devices that emit blue light, including eReaders, laptops, cell phones and LED monitors.

“In the past 50 years, there has been a decline in average sleep duration and quality,” said Charles Czeisler, the HMS Frank Baldino, Jr., Ph.D. Professor of Sleep Medicine and chief of the Brigham and Women’s Division of Sleep and Circadian Disorders. “Since more people are choosing electronic devices for reading, communication and entertainment, particularly children and adolescents who already experience significant sleep loss, epidemiological research evaluating the long-term consequences of these devices on health and safety is urgently needed.”

Researchers emphasize the importance of these findings, given recent evidence linking chronic suppression of melatonin secretion by nocturnal light exposure with the increased risk of breast cancer, colorectal cancer and prostate cancer.

LIGHT-EMITTING E-READERS BEFORE BEDTIME CAN ADVERSELY IMPACT SLEEP

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Use of a light-emitting electronic device (LE-eBook) in the hours before bedtime can adversely impact overall health, alertness, and the circadian clock which synchronizes the daily rhythm of sleep to external environmental time cues, according to researchers at Brigham and Women’s Hospital (BWH) who compared the biological effects of reading an LE-eBook compared to a printed book.  These findings of the study are published in the Proceedings of the National Academy of Sciences on December 22, 2014.

“We found the body’s natural circadian rhythms were interrupted by the short-wavelength enriched light, otherwise known as blue light, from these electronic devices,” said Anne-Marie Chang, PhD, corresponding author, and associate neuroscientist in BWH’s Division of Sleep and Circadian Disorders. “Participants reading an LE-eBook took longer to fall asleep and had reduced evening sleepiness, reduced melatonin secretion, later timing of their circadian clock and reduced next-morning alertness than when reading a printed book.”

Previous research has shown that blue light suppresses melatonin, impacts the circadian clock and increase alertness, but little was known about the effects of this popular technology on sleep.   The use of light emitting devices immediately before bedtime is a concern because of the extremely powerful effect that light has on the body’s natural sleep/wake pattern, and may thereby play a role in perpetuating sleep deficiency.

During the two-week inpatient study, twelve participants read LE-e-Books on an iPad for four hours before bedtime each night for five consecutive nights. This was repeated with printed books.  The order was randomized with some reading the iPad first and others reading the printed book first.  Participants reading on the iPad took longer to fall asleep, were less sleepy in the evening, and spent less time in REM sleep.  The iPad readers had reduced secretion of melatonin, a hormone which normally rises in the evening and plays a role in inducing sleepiness.  Additionally, iPad readers had a delayed circadian rhythm, indicated by melatonin levels, of more than an hour.  Participants who read from the iPad were less sleepy before bedtime, but sleepier and less alert the following morning after eight hours of sleep.  Although iPads were used in this study, BWH researchers also measured other eReaders, laptops, cell phones, LED monitors, and other electronic devices, all emitting blue light.

“In the past 50 years, there has been a decline in average sleep duration and quality,” stated Charles Czeisler, PhD, MD, FRCP, chief, BWH Division of Sleep and Circadian Disorders.   “Since more people are choosing electronic devices for reading, communication and entertainment, particularly children and adolescents who already experience significant sleep loss, epidemiological research evaluating the long-term consequences of these devices on health and safety is urgently needed.”

Researchers emphasize the importance of these findings, given recent evidence linking chronic suppression of melatonin secretion by nocturnal light exposure with the increased risk of breast cancer, colorectal cancer and prostate cancer.