Nighttime Screen Use Linked to Poorer Sleep Quality & Shorter Duration

The AHA! Team — Mon, 09 Jun 2025 05:22:58 +0000

Dr. Priyom Bose, Ph.D. via News-Medical – Bedtime screen time cuts sleep by nearly an hour a week and boosts the risk of restless nights, especially for night owls. A recent JAMA Network Open study examines how electronic screen use before bed affects sleep among adults. How does light affect sleep quality? Although adequate and high-quality sleep is crucial for good health, average sleep duration and quality have deteriorated in the past several decades. In fact, one recent study revealed that approximately one-third of adults do not meet recommended guidelines to sleep at least seven to nine hours each night. The eyes contain photosensitive cells in the retina, which is extremely sensitive to light. The absence of light at night increases the secretion of melatonin, a hormone that is essential for inducing the feeling of sleepiness. Thus, exposure to bright light before sleep delays melatonin secretion, thereby increasing sleep latency and disrupting circadian rhythm. Smartphone use and chronotype Smartphone devices use light-emitting diodes (LEDs) for screen illumination. The light intensity in these devices generally peaks in the 450 nm range, which corresponds to the blue spectrum of light that has been shown to negatively affect human sleep. As a result, smartphone users often experience sleep disruptions due to habit of looking at device screens before sleep. To date, most studies have evaluated the effects of electronic screen use on sleep based on adolescent and young adult study participants, partly because this population more frequently uses new technologies. Since adolescents are less sensitive to light-induced sleep disruptions, it is crucial to investigate the differential impact of electronic screen use before sleep among individuals of all ages. About the study The researchers of the current study conducted a cross-sectional analysis on data obtained from the American Cancer Society Cancer Prevention Study-3 (CPS-3) to investigate whether electronic screen use before sleeping affects sleep outcomes. The CPS-3 study cohort comprised both men and women from 35 U.S. states and Puerto Rico. To measure electronic screen use before sleep, study participants were asked to self-report their sleeping patterns. For example, study participants were asked how often every week they watch or read on an electronic screen, such as a smartphone, laptop, or tablet, but not TV. Falling asleep and Waking up Except for weekends and non-workdays, study participants reported the average time at which they tried to fall asleep and wake up. Sleep duration was calculated in minutes, with sleep quality assessed based on Pittsburgh Sleep Quality Index. Chronotype was determined using the Horne-Östberg Morningness-Eveningness Questionnaire. The effect of electronic screen use on sleep was assessed based on prevalence ratios (PRs) using a Poisson regression model. Study findings The current study included 122,058 individuals with a median age of 56 years. Over 89% of study participants were White, whereas 58% and 80% completed a college degree and were women, respectively. About 58% of study participants were classified as morning chronotypes, with less than 6% reporting using an eye mask while sleeping. Approximately 81% of the study cohort reported that their bedrooms were dark enough that they could not see across the room. Over 41% of the study cohort reported the use of an electronic screen every night of the week before sleeping. The remaining study participants either occasionally used electronic screens before sleep or did not use them at all. As compared to the overall population, non-users were more likely to be male or at least 60 years of age. Individuals who engaged with electronic screens daily were more likely to achieve less than the recommended sleep duration. Age- and sex-adjusted models revealed that, as compared to non-users, daily screen users slept a mean of 7.78 fewer minutes. Daily electronic screen users also reported 19.01 minutes later bedtimes on workdays, with these durations fluctuating on weekends and non-workdays. Daily electronic screen use was associated with a 26% increased risk of self-reported poor sleep quality. Fully adjusted models revealed that daily electronic screen users went to bed 18.82 and 19.69 minutes later on workdays and non-workdays, respectively. As compared to study participants who did not report screen time, 33% of those who used electronic screens daily reported poor sleep quality. Individuals with the morning chronotype went to sleep 34 minutes earlier on workdays and non-workdays. However, those with evening chronotypes reported later bedtimes. Conclusions Daily electronic screen use before sleep was associated with 48 fewer minutes of sleep each week. As compared to those with morning chronotypes, individuals with later chronotypes experience poor sleep quality and duration. In the future, additional research is needed to understand the underlying mechanisms through which screen use disturbs sleep. Journal reference: Zhong, C., Masters, M., Donzella, S. M., et al. (2025) Electronic Screen Use and Sleep Duration and Timing in Adults. JAMA Network Open 8(3):e252493. doi:10.1001/jamanetworkopen.2025.2493 To read the original article click here.

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Study Links Exposure to Nighttime Artificial Lights with Elevated Thyroid Cancer Risk

AHA Publisher — Mon, 08 Feb 2021 08:00:54 +0000

Wiley via EurekAlert – People living in regions with high levels of outdoor artificial light at night may face a higher risk of developing thyroid cancer. The finding comes from a study published early online in CANCER, a peer-reviewed journal of the American Cancer Society. Over the past century, nightscapes–especially in cities–have drastically changed due to the rapid growth of electric lighting. Also, epidemiological studies have reported an association between higher satellite-measured levels of nighttime light and elevated breast cancer risk. Because some breast cancers may share a common hormone-dependent basis with thyroid cancer, a team led by Qian Xiao, PhD, of The University of Texas Health Science Center at Houston School of Public Health, looked for an association between light at night and later development of thyroid cancer among participants in the NIH-AARP Diet and Health Study, which recruited American adults aged 50 to 71 years in 1995-1996. The investigators analyzed satellite imagery data to estimate levels of light at night at participants’ residential addresses, and they examined state cancer registry databases to identify thyroid cancer diagnoses through 2011. Among 464,371 participants who were followed for an average of 12.8 years, 856 cases of thyroid cancer were diagnosed (384 in men and 472 in women). When compared with the lowest quintile of light at night, the highest quintile was associated with a 55 percent higher risk of developing thyroid cancer. The association was primarily driven by the most common form of thyroid cancer, called papillary thyroid cancer, and it was stronger in women than in men. In women, the association was stronger for localized cancer with no sign of spread to other parts of the body, while in men the association was stronger for more advanced stages of cancer. The association appeared to be similar for different tumor sizes and across participants with different sociodemographic characteristics and body mass index. The researchers noted that additional epidemiologic studies are needed to confirm their findings. If confirmed, it will be important to understand the mechanisms underlying the relationship between light at night and thyroid cancer. The scientists noted that light at night suppresses melatonin, a modulator of estrogen activity that may have important anti-tumor effects. Also, light at night may lead to disruption of the body’s internal clock (or circadian rhythms), which is a risk factor for various types of cancer. “As an observational study, our study is not designed to establish causality. Therefore, we don’t know if higher levels of outdoor light at night lead to an elevated risk for thyroid cancer; however, given the well-established evidence supporting a role of light exposure at night and circadian disruption, we hope our study will motivate researchers to further examine the relationship between light at night and cancer, and other diseases,” said Dr. Xiao. “Recently, there have been efforts in some cities to reduce light pollution, and we believe future studies should evaluate if and to what degree such efforts impact human health.” To read the original article click here.

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Nighttime Screen Use Linked to Poorer Sleep Quality & Shorter Duration

Study Links Exposure to Nighttime Artificial Lights with Elevated Thyroid Cancer Risk