In this day and age, so much of our time is spent in front of screens. Does all the hype around studies showing that the use of screens can mess with your sleep make sense?

Human sleep and wakefulness periods follow a natural, circadian rhythm of about 24 hours. Although circadian rhythms can persist without environmental cues, they are normally modulated by external timing cues that adapt the rhythm to the environment, the most obvious example being sunlight.

To synchronize physiological processes with the day-night cycle, the biological clock must detect decreases in light levels as night approaches. These light changes are sensed by specialized cells in the retina called intrinsic photosensitive retinal ganglion cells.

These cells contain a photopigment called melanopsin that allows them to be activated by light. Information is then sent to the brain where it regulates the pineal gland’s synthesis of the sleep-promoting neurohormone melatonin. Melatonin is secreted into the bloodstream where it modulates the pathways that ultimately control the sleep–wake cycle. Melatonin synthesis increases as the light in the environment decreases and reaches a maximum between 2 a.m. and 4 a.m. Anything that interferes with these light cues will most likely affect sleep cycles.

Electronic devices emit short-wavelength–enriched light, otherwise known as blue light. This has been shown to suppress melatonin production and increase alertness, probably due to the high sensitivity of melanopsin to blue light. Blue light-emitting devices are everywhere and include anything using LEDs: LED light bulbs, laptops, tablets, cell phones, LED TVs and even LED digital clocks. All of these devices have the ability to affect melatonin production and potentially mess with your sleep cycles.

However, until recently, little was actually known about the effects of light-emitting devices on sleep. A study just published in the Proceedings of the National Academy of Sciences (PNAS) addressed this question. The authors compared the biological effects of reading an e-book on a light-emitting device with reading a printed book in the hours before bedtime. Participants were asked to either read on an iPad for four hours before bedtime each night for five consecutive nights, or do the same with a printed book.

They found that participants reading in a light emitting device in the hours before bedtime had decreased sleepiness, took longer to fall asleep, and had decreased REM sleep. It was also found that the late evening rise of pineal melatonin secretion was suppressed during the time that the electronic device was being used, and that the phase of their circadian clock that drives melatonin secretion, sleep propensity, and REM sleep propensity was delayed. In the following morning, after eight hours of sleep, participants reading on an iPad felt sleepier and less alert.

What makes it really serious is that this is a routine. The continued use of light emitting devices immediately before bedtime is a concern because it can perpetuate sleep deficiency. In the last decades, there has been a decline in average sleep duration and quality, and the use of technological devices has most likely contributed significantly to this pattern.

According to a recent poll, 90% of Americans use some form of technological device in the hour before sleep, including TVs (60%), cell phones (39%), computers (36%), electronic music devices (29%), telephones (21%), video game consoles (8%) and e-book readers (6%).

Chronic sleep deprivation is known to have adverse effects on general health, including a higher propensity to obesity, hypertension, heart attack, stroke, stress, depression, and memory and cognitive impairment. Chronic suppression of melatonin secretion by nocturnal light exposure due to shift work has even been associated with increased risk of breast, colorectal, and advanced prostate cancer.

This is indeed serious. By all means, read a book before bedtime. Just make it a real book made of paper.

References

Cajochen C, Frey S, Anders D, Späti J, Bues M, Pross A, Mager R, Wirz-Justice A, & Stefani O (2011). Evening exposure to a light-emitting diodes (LED)-backlit computer screen affects circadian physiology and cognitive performance. Journal of applied physiology (Bethesda, Md. : 1985), 110 (5), 1432-8 PMID: 21415172

Chang A, Aeschbach D, Duffy JF, & Czeisler CA (2014). Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences of the United States of America PMID: 25535358

Chellappa SL, Steiner R, Blattner P, Oelhafen P, Götz T, & Cajochen C (2011). Non-visual effects of light on melatonin, alertness and cognitive performance: can blue-enriched light keep us alert? PloS one, 6 (1) PMID: 21298068

Gradisar M, Wolfson AR, Harvey AG, Hale L, Rosenberg R, & Czeisler CA (2013). The sleep and technology use of Americans: findings from the National Sleep Foundation’s 2011 Sleep in America poll. Journal of clinical sleep medicine : JCSM : official publication of the American Academy of Sleep Medicine, 9 (12), 1291-9 PMID: 24340291

Straif K, Baan R, Grosse Y, Secretan B, El Ghissassi F, Bouvard V, Altieri A, Benbrahim-Tallaa L, & Cogliano V (2007). Carcinogenicity of shift-work, painting, and fire-fighting. The Lancet. Oncology, 8 (12), 1065-6 PMID: 19271347

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