A recent study conducted by a Harvard Medical School team showed that poor quality of sleep was linked to reading on light-emitting digital devices before bedtime. The study examined how reading traditional paper books and digital devices reflecting LED lighting at night affected how well participants were able to sleep. The research findings were published in the Proceedings of the National Academy of Sciences.

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Sleep deprivation impacts on daytime functioning, and over time may contribute to the development of serious health conditions. Lack of sleep increases the risk of developing cardiovascular diseases and other chronic health disorders such as diabetes.

Sleep quality is reliant on the production of melatonin. Readers reading on an e-book reader before going to sleep may have their ability to sleep well reduced as the production of melatonin, the sleep-promoting hormone, is inhibited.

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The blue light emitted by the electronic devices shines directly into the reader's eyes as opposed to the reflected light when reading off the printed pages of a book.

Researchers have found that during the reading on the iPad segment of the experiment, participants showed the following biological effects:

· longer time taken in falling asleep

· delays the circadian clock

· decrease in melatonin secretion

· decrease in timing and duration of REM sleep

· reduced levels of alertness experienced the next morning

Anne-Marie Chang, assistant professor of biobehavioural health at the Pennsylvania State University and one of the leading researchers of the study, said that when compared with natural light, the light produced by digital devices has a greater concentration of blue light - with a top level around 450 nm.

How the sleep quality study was conducted

The sleep quality study centred around twelve healthy young individuals who were placed in a closed sleep laboratory at Brigham and Women's Hospital. Participants were required to indulge in 'leisurely reading' for four hours every evening from 6-10 pm over a five day period and then an additional five days with participants reading from an iPad device for the same length of time..

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It took study subjects a longer time - as much as 10 minutes longer - to fall asleep after reading on the digital device. As a result sleep quality was negatively affected and subjects did not receive the usual benefits derived from a good night's sleep.

Analysis of blood samples taken regularly indicated a decrease in melatonin production during the period requiring subjects to read from the digital device.

As part of the experiment, researchers made use of a polysomnograph to study brain waves, heart rate, breathing and eye movements. The device further helped researchers to:

· establish the length of time it takes to fall asleep

· duration of sleep time

· length of sleep time in each stage of sleep

Participants were also required to fill out the Karolinska Sleepiness Scale that was used to assess their sleepiness.

Recommendations made by Harvard Medical School's sleep quality study

Findings resulting from the sleep quality study suggest that in order to improve quality of sleep, e-book readers should reduce the length of time spent reading on digital devices that emit blue light wavelengths before going to sleep..

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