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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.
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.