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The iPad Hangover

Evening use of light-emitting eReaders negatively affects sleep, circadian timing and next-morning alertness.

Study under review: Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness

Introduction

Within the last few decades there have been massive developments in portable technology. High-powered devices have now become lightweight, convenient, and affordable. Many activities, like book reading, have been digitized. With the development of this technology, what once had been a common pastime to help get us to sleep may now actually be doing the opposite by causing a shift in our circadian rhythm for sleep.

A circadian rhythm is essentially an organism's daily internal clock. In humans it accounts for many of our physiological fluctuations throughout the day. A major molecule that affects our sleep biorhythms is melatonin. Many have heard of melatonin used as a sleep aid, and for good reason. Melatonin is a hormone that is released by the pineal gland in the brain and is involved with sleepiness and sleep regulation.

Melatonin production is heavily influenced by sunlight interacting with retinal pigments. When light hits the retina, arylalkylamine N-acetyltransferase production is depressed[1]. Arylalkylamine N-acetyltransferase is an enzyme that catalyzes a crucial step in melatonin biosynthesis. Therefore, when light is absent, melatonin concentration builds and sleepiness ensues.

What happens when the retina is exposed to light during sleepy time hours? Research has shown that exposure to artificial light at night suppresses melatonin levels[2] and increases alertness[3]. When melatonin is suppressed, the body is tricked into thinking it is still daytime and the circadian rhythm can shift[4], especially when this happens repeatedly. This shift makes it difficult to fall asleep. When a person can’t sleep due to (light-induced) melatonin suppression, that signals there has been a shift in the biological clock, relative to the normal 24-hour circadian cycle. As seen in Figure 1, levels of hormones in the body such as melatonin and cortisol fluctuate throughout the day. If the time course of one hormone is thrown out of whack, sleep and other physiological outcomes may be shifted as well.

Figure 1: Variation in melatonin and cortisol throughout the day

But why is this a problem? There is no definitive explanation[5] as to why we need sleep, but we know that chronic deprivation is detrimental to our immune system[6], ability to perform[7], memory[8], and a laundry list of other things in regard to general health.

Without question, sleep is important. In fact, chronic suppression of melatonin via evening light exposure has serious implicated health risks, such as cancer[9]. Such conditions are frequently seen in shift-workers, like nurses and fire fighters. The International Agency for Research on Cancer, an agency directly related to the World Health Organization, has classified shift-working as a probable carcinogen. Shift work represents an extreme of altered sleep patterns, but the mechanisms behind cancer incidence due to altered melatonin secretion and circadian rhythm shifts have been widely researched[10].

Cancer risk aside, there are other legitimate reasons to study this phenomena, as it directly relates to performance (both mental and physical) and general health. The aim of this study is to quantify the effects of light-induced melatonin suppression, caused by iPad use before sleep, on sleep quality and feelings of lingering sleepiness after waking up.

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Other Articles in Issue #04 (February 2015)