Light-emitting e-readers detrimentally shift circadian clock

December 22, 2014

You may think your e-reader is helping you get to sleep at night, but it might actually be harming your quality of sleep, according to researchers. Exposure to light during evening and early nighttime hours suppresses release of the sleep-facilitating hormone melatonin and shifts the circadian clock, making it harder to fall asleep at bedtime.

"Electronic devices emit light that is short-wavelength-enriched light, which has a higher concentration of blue light -- with a peak around 450 nm -- than natural light," said Anne-Marie Chang, assistant professor of biobehavioral health, Penn State. "This is different from natural light in composition, having a greater impact on sleep and circadian rhythms."

Chang and colleagues observed 12 adults for two weeks, comparing when the participants read from an iPad, serving as an e-reader, before bedtime to when they read from a printed book before bedtime. The researchers monitored the participants' melatonin levels, sleep and next-morning alertness, as well as other sleep-related measures.

Participants took nearly 10 minutes longer to fall asleep and had a significantly lower amount of REM -- rapid eye movement -- sleep after reading from a light-emitting e-reader than they did after reading from a print book, the researchers report in today's (Dec. 22) issue of the Proceedings of the National Academy of Science.

"Our most surprising finding was that individuals using the e-reader would be more tired and take longer to become alert the next morning," said Chang. "This has real consequences for daytime functioning, and these effects might be worse in the real world as opposed to the controlled environment we used."

The researchers measured the amount of brightness coming from several devices, including an iPad, iPhone, Kindle, Kindle Fire and Nook Color. The Kindle e-reader does not emit light, while the iPad, Kindle Fire and Nook Color emit similar amounts of light. However, the iPad is the brightest of the devices measured.

The study participants were admitted to Brigham and Women's Hospital in Boston for the duration of the 14-day study, in order for the researchers to control for many factors. Each participant read from an iPad before bedtime for five nights in a row, and did the same with a printed book. It was randomly determined whether a participant read from a print book or an iPad first -- the results showed that the order didn't make a difference. Participants were able to choose their own reading material, as long as it could be considered "leisure" reading and did not contain any images or puzzles, only text.

The subjects read for four hours before bed, from 6 p.m. to 10 p.m., with time designated for sleep from 10 p.m. to 6 a.m. The researchers collected blood samples from the readers hourly to measure melatonin. Polysomnography -- which records brain waves, heart rate, breathing and eye movements -- was also used to determine how long it took to fall asleep, the amount of time spent asleep and the amount of time spent in each sleep stage. The researchers also used the Karolinska Sleepiness Scale to measure subjective sleepiness.

"We live in a sleep-restricted society, in general," said Chang. "It is important to further study the effects of using light-emitting devices, especially before bed, as they may have longer term health consequences than we previously considered."
-end-
Chang was in the division of sleep and circadian disorders, department of medicine, Brigham and Women's Hospital and the division of sleep medicine, Harvard Medical School at the time the study was conducted. Also working on this research were Daniel Aeschbach, Jeanne F. Duffy and Charles A. Czeisler, all in the division of sleep and circadian disorders, department of medicine, Brigham and Women's Hospital and the division of sleep medicine, Harvard Medical School. Aeschbach is also affiliated with the Institute of Aerospace Medicine, German Aerospace Center. The National Institutes of Health and the National Center for Research Resources supported this research.

Penn State

Related Sleep Articles from Brightsurf:

Size and sleep: New research reveals why little things sleep longer
Using data from humans and other mammals, a team of scientists including researchers from the Santa Fe Institute has developed one of the first quantitative models that explains why sleep times across species and during development decrease as brains get bigger.

Wind turbine noise affects dream sleep and perceived sleep restoration
Wind turbine noise (WTN) influences people's perception of the restorative effects of sleep, and also has a small but significant effect on dream sleep, otherwise known as REM (rapid eye movement) sleep, a study at the University of Gothenburg, Sweden, shows.

To sleep deeply: The brainstem neurons that regulate non-REM sleep
University of Tsukuba researchers identified neurons that promote non-REM sleep in the brainstem in mice.

Chronic opioid therapy can disrupt sleep, increase risk of sleep disorders
Patients and medical providers should be aware that chronic opioid use can interfere with sleep by reducing sleep efficiency and increasing the risk of sleep-disordered breathing, according to a position statement from the American Academy of Sleep Medicine.

'Short sleep' gene prevents memory deficits associated with sleep deprivation
The UCSF scientists who identified the two known human genes that promote 'natural short sleep' -- nightly sleep that lasts just four to six hours but leaves people feeling well-rested -- have now discovered a third, and it's also the first gene that's ever been shown to prevent the memory deficits that normally accompany sleep deprivation.

Short sleep duration and sleep variability blunt weight loss
High sleep variability and short sleep duration are associated with difficulties in losing weight and body fat.

Nurses have an increased risk of sleep disorders and sleep deprivation
According to preliminary results of a new study, there is a high prevalence of insufficient sleep and symptoms of common sleep disorders among medical center nurses.

Common sleep myths compromise good sleep and health
People often say they can get by on five or fewer hours of sleep, that snoring is harmless, and that having a drink helps you to fall asleep.

Sleep tight! Researchers identify the beneficial role of sleep
Why do animals sleep? Why do humans 'waste' a third of their lives sleeping?

Does extra sleep on the weekends repay your sleep debt? No, researchers say
Insufficient sleep and untreated sleep disorders put people at increased risk for metabolic problems, including obesity and diabetes.

Read More: Sleep News and Sleep Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.