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sexta-feira, 9 de janeiro de 2015

eReaders podem alterar o ritmo de sono-vigília (386)


UNIVADIS - MSD - Copyright © 2015 Merck Sharp & Dohme Corp., filial da Merck & co., Inc. Whitehouse Station, Nova Jersey, EUA.

O uso de eReaders que emitem luz, pouco antes de ir dormir, pode alterar o ritmo de sono-vigília da pessoa. Cientistas dos EUA chegaram a essa conclusão em um estudo publicado na revista “PNAS”. A secreção de melatonina foi significativamente reduzida durante a leitura.

Para o estudo, que foi conduzido pela Universidade de Harvard, em Boston (Massachusetts), foi pedido a doze adultos jovens que lessem livros impressos e livros digitais antes de dormir sob condições controladas. Durante cinco noites consecutivas, os participantes leram eBooks e, durante mais cinco noites consecutivas, eles leram livros impressos. O período de leitura durou quatro horas todas as vezes, das 18h até as 22h. Em seguida a luz foi desligada até as 6h, quando os participantes foram acordados. Houve um dia de intervalo entre as duas fases.
O estudo demonstrou que os sujeitos do estudo que usaram eReaders levaram, em média, dez minutos a mais para conseguir dormir. Adicionalmente, suas fases REM foram aproximadamente doze minutos mais curtas e eles se sentiram significativamente mais sonolentos na manhã seguinte. A diferença na secreção de melatonina foi particularmente evidente. Dentre os participantes usando eReaders, a secreção foi 55 por cento menor. Após cinco noites com quatro horas de leitura usando dispositivos digitais, o relógio circadiano dos participantes foi retardado em uma média de 1,5 horas.
Estudos anteriores também indicaram que a luz de ondas curtas (azul) atua como um sinal de alerta em humanos, resultando na supressão do sono e na redução da secreção do hormônio do sono pelo corpo, disseram os pesquisadores.
“Nossos resultados confirmam que a luz elétrica ao qual somos expostos entre o pôr do sol e a hora em que vamos dormir apresenta amplos efeitos biológicos”, disseram os autores sob a liderança de Anne-Marie Chang. Contudo, eles chamaram atenção para o fato de que a luz dos eReaders estava acesa na potência máxima, enquanto os participantes usavam uma luz suave na leitura dos livros impressos.

Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness
Edited by Joseph S. Takahashi, Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX, and approved November 26, 2014 (received for review September 24, 2014)
Significance
The use of light-emitting electronic devices for reading, communication, and entertainment has greatly increased recently. We found that the use of these devices before bedtime prolongs the time it takes to fall asleep, delays the circadian clock, suppresses levels of the sleep-promoting hormone melatonin, reduces the amount and delays the timing of REM sleep, and reduces alertness the following morning. Use of light-emitting devices immediately before bedtime also increases alertness at that time, which may lead users to delay bedtime at home. Overall, we found that the use of portable light-emitting devices immediately before bedtime has biological effects that may perpetuate sleep deficiency and disrupt circadian rhythms, both of which can have adverse impacts on performance, health, and safety.
Abstract
In the past 50 y, there has been a decline in average sleep duration and quality, with adverse consequences on general health. A representative survey of 1,508 American adults recently revealed that 90% of Americans used some type of electronics at least a few nights per week within 1 h before bedtime. Mounting evidence from countries around the world shows the negative impact of such technology use on sleep. This negative impact on sleep may be due to the short-wavelength–enriched light emitted by these electronic devices, given that artificial-light exposure has been shown experimentally to produce alerting effects, suppress melatonin, and phase-shift the biological clock. A few reports have shown that these devices suppress melatonin levels, but little is known about the effects on circadian phase or the following sleep episode, exposing a substantial gap in our knowledge of how this increasingly popular technology affects sleep. Here we compare the biological effects of reading an electronic book on a light-emitting device (LE-eBook) with reading a printed book in the hours before bedtime. Participants reading an LE-eBook took longer to fall asleep and had reduced evening sleepiness, reduced melatonin secretion, later timing of their circadian clock, and reduced next-morning alertness than when reading a printed book. These results demonstrate that evening exposure to an LE-eBook phase-delays the circadian clock, acutely suppresses melatonin, and has important implications for understanding the impact of such technologies on sleep, performance, health, and safety.
Present address: Department of Biobehavioral Health, Pennsylvania State University, University Park, PA 16802.
To whom correspondence should be addressed. Email: amchang@psu.edu.
Author contributions: A.-M.C., J.F.D., and C.A.C. designed research; A.-M.C. performed research; A.-M.C. and D.A. analyzed data; and A.-M.C. and C.A.C. wrote the paper.
Conflict of interest statement: Dr. Czeisler has received consulting fees from or served as a paid member of scientific advisory boards for: Boston Celtics; Boston Red Sox; Citgo Inc.; Cleveland Browns; Merck; Novartis; Purdue Pharma LP; Quest Diagnostics, Inc.; Teva Pharmaceuticals Industries Ltd.; Valero Inc.; Vanda Pharmaceuticals, Inc. Dr. Czeisler currently owns an equity interest in Lifetrac, Inc.; Somnus Therapeutics, Inc.; Vanda Pharmaceuticals, Inc., and between October 2012 and October 2013, Apple, Inc. and Microsoft, Inc. Dr. Czeisler received royalties from McGraw Hill, Penguin Press/Houghton Mifflin Harcourt, and Philips Respironics, Inc. and has received grants and research support from Cephalon Inc., National Football League Charities, Philips Respironics, ResMed Foundation, San Francisco Bar Pilots and Sysco. Dr. Czeisler is the incumbent of an endowed professorship provided to Harvard University by Cephalon, Inc. and holds a number of process patents in the field of sleep/circadian rhythms (e.g., photic resetting of the human circadian pacemaker). Since 1985, Dr. Czeisler has also served as an expert witness on various legal cases related to sleep and/or circadian rhythms, including matters involving Bombardier, Inc.; Delta Airlines; FedEx; Greyhound; Michael Jackson's mother and children; Purdue Pharma, L.P.; United Parcel Service and the United States of America.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1418490112/-/DCSupplemental.

Freely available online through the PNAS open access option.

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