Kindle Paperwhite light interferes with sleep

Reading e-books in the evening can lead to difficulty sleeping

According to a study, eBook readers with lighting impair the biological clock with measurable consequences

It is possible that the number of people who own an eBook reader will increase this Christmas. And this could also increase the number of people who use it in the evening or at night in bed because it is easier to hold, but also because the lighting makes it easier to read. But according to a study, this can have consequences that may make print books more attractive as bedtime reading again.

It is known that exposure to artificial light at night can cause sleep disorders. This is not only a problem with shift workers, but also in general because people are awake longer and longer and are exposed to light from lighting and screens. Short-wave light in particular inhibits the release of melatonin and shifts the biological clock. This keeps you more alert, but it is harder to fall asleep. The hormone regulates the day-night cycle.

Since there is already a lot of evidence that screen light can have a negative impact on sleep, and a survey in the USA showed that 90 percent of people have an electronic device an hour before bed an hour several days a week A team of American and German scientists is now investigating how the use of illuminated eBook readers shortly before falling asleep affects sleep. The study has been published online in advance in PNAS (Proceedings of the National Academy of Sciences of the United States of America).

12 young subjects were asked to keep a log for 14 days and to read an eBook on a lighted reader for about four hours on 5 consecutive days before going to bed and then or before a book in dim lighting for four hours before going to bed read. Whoever reads eBooks or books first was chosen at random. A blood sample was taken every hour while reading to determine the melatonin concentration. On the 4th and 5th evenings, polysomnography was used to record the time that elapsed between switching off the light and falling asleep. In addition, the sleep time and the time spent in the various sleep phases were measured. The test subjects indicated their fatigue in the evening and in the morning on a scale. An EEG was taken for each reading phase on two evenings and two mornings.

The sample is very small and very young, with an average age of 25 years. It is therefore difficult to assess how meaningful the experiment is. In addition, habituation effects could occur even after longer than 5 days. It is also clear that a similar exposure to other screens is likely to have similar effects as those observed on the eBook readers, which were set to maximum lighting. Like other light-emitting screens, these emit short-wave light, which is not the case with books whose sides reflect white light. Studies have shown that exposure to short-wave light has greater effects on the human day-night rhythm than exposure to long-wave light - regardless of the illuminance (lux).

When reading books, so the result, the release of melatonin is not delayed, but clearly when reading illuminated eBooks. Even in the evening after the last eBook was read, the release of melatonin is delayed by 1.5 hours. The eBook readers needed an average of 10 minutes longer to fall asleep, had shorter REM sleep phases, and no differences were found on the other sleep phases or on the length of sleep. The eBook readers were less tired in the evening and showed less strong delta / theta brain waves on the EEG, but they were more tired in the morning and took longer to feel awake.

The researchers conclude that reading eBooks before sleep can affect user performance, health, and safety by changing the biological clock, increasing sleep time, delaying melatonin secretion, and shortening REM periods. This is particularly worrying because according to studies, chronic suppression of melatonin secretion appears to cause an increased risk of breast, colon and prostate cancer in shift workers. Since the release of melatonin and thus the biological clock is delayed by 1.5 hours, there is a great risk that reading eBooks before going to bed can lead to sleep disorders, including chronic ones.

The researchers point out that the average teen in the US is exposed to media an average of 7.5 hours a day, especially in the afternoons and evenings before bed. This includes all devices that emit light such as televisions, tablets, notebooks, smartphones, game consoles, etc. That would mean that the 4 hours of reading an eBook before going to sleep are everyday or evenings for many children and young people - and thus possibly also the observed consequences of this Experiments. It is therefore important to examine the physiological influence of exposure to light from technical devices in more detail. This could have consequences for learning and development in children, and the physiological and medical long-term effects may have been underestimated so far. (Florian Rötzer)

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