Effects of smartphone use with and without blue light at night in healthy adults: A randomized, double-blind, cross-over, placebo-controlled comparison

https://doi.org/10.1016/j.jpsychires.2016.12.010Get rights and content

Abstract

Smartphones deliver light to users through Light Emitting Diode (LED) displays. Blue light is the most potent wavelength for sleep and mood. This study investigated the immediate effects of smartphone blue light LED on humans at night. We investigated changes in serum melatonin levels, cortisol levels, body temperature, and psychiatric measures with a randomized, double-blind, cross-over, placebo-controlled design of two 3-day admissions. Each subject played smartphone games with either conventional LED or suppressed blue light from 7:30 to 10:00PM (150 min). Then, they were readmitted and conducted the same procedure with the other type of smartphone. Serum melatonin levels were measured in 60-min intervals before, during and after use of the smartphones. Serum cortisol levels and body temperature were monitored every 120 min. The Profile of Mood States (POMS), Epworth Sleepiness Scale (ESS), Fatigue Severity Scale (FSS), and auditory and visual Continuous Performance Tests (CPTs) were administered. Among the 22 participants who were each admitted twice, use of blue light smartphones was associated with significantly decreased sleepiness (Cohen's d = 0.49, Z = 43.50, p = 0.04) and confusion-bewilderment (Cohen's d = 0.53, Z = 39.00, p = 0.02), and increased commission error (Cohen's d = −0.59, t = −2.64, p = 0.02). Also, users of blue light smartphones experienced a longer time to reach dim light melatonin onset 50% (2.94 vs. 2.70 h) and had increases in body temperature, serum melatonin levels, and cortisol levels, although these changes were not statistically significant. Use of blue light LED smartphones at night may negatively influence sleep and commission errors, while it may not be enough to lead to significant changes in serum melatonin and cortisol levels.

Introduction

Smartphones have become ubiquitous in daily life. The average smartphone use time is increasing and nearly doubled from 98 min in 2011 to 195 min in 2013 (Sale and Scott, 2014). A nationwide community survey conducted in the United States reported that 39% of Americans used cell phones in their bedroom in the hour prior to sleep; the rate was twice as high in adolescents and young adults (Gradisar et al., 2013). Smartphones are often equipped with a light-emitting diodes (LED) display, which delivers bright light to the human eye. Smartphone LED light is an important source of artificial light at night (ALAN). ALAN influences the circadian regulation of the sleep-wake cycle (Gonzalez and Aston-Jones, 2006), suppresses melatonin secretion (Czeisler et al., 1995, Lewy et al., 1980), alters mood and cognitive functions (LeGates et al., 2012), and contributes to fatigue (Meesters and Lambers, 1990).

Advantages of LED display over incandescent light sources include lower energy consumption, longer lifespan of electronic devices. However, LED-based light sources differ from traditional lamps in that they contain higher proportions of short-wavelength blue light ranging from 450 to 470 nm, which is more likely to cause problems, such as blue light hazard, when people look directly into these bright and point-like sources at night (Federation of National Manufacturers' Associations for Luminaires and Electrotechnical Components for Luminaires, 2011). Blue light hazard is defined as the potential for a photochemical induced retinal injury resulting from electromagnetic radiation exposure of short-wavelength blue light (Algvere et al., 2006).

Also, compared to light with longer wavelengths, light of short wavelength has been shown to have a larger suppressing effect on melatonin concentrations (Brainard et al., 2001, Cajochen et al., 2005). Not all studies have found effects of melatonin suppression when blue light devices have been used at night (Heath et al., 2014, Wood et al., 2013). However, Wood et al. mentioned that exposure to blue light LED of self-luminous tablets significantly reduced melatonin levels after 2 h, compared to orange LED (Wood et al., 2013).

Blue light therapy in the morning may be effective for the treatment of depression with a seasonal pattern (Gagne et al., 2011) and depression among the elderly (Lieverse et al., 2011), but blue light exposure at night and in relatively low room light conditions increases secretion of human melatonin and can thus lead to insomnia (Chellappa et al., 2013) and increased vigilance among night workers (Sasseville et al., 2006). Smartphone users exposed to bright blue light from the phone's LED display at night may be affected as well. However, no previous controlled studies have addressed this issue.

The purpose of the present study was to investigate the impact of smartphone LED displays with blue light at night, compared to LED displays with suppressed blue light. The two types of LED displays were indistinguishable from each other with the naked eye because other wavelengths were used to mimic blue light in the suppressed LED. The main hypothesis was that exposure to a smartphone LED display with blue light at night suppresses melatonin increase, decreases sleepiness, and impairs cognitive performance, compared to the effects of the smartphone LED display without blue light.

Section snippets

Subjects

Subjects were recruited through advertisement. All study subjects were recruited at the Samsung Medical Center from September 2013 to February 2014 through web postings and online advertisements. Eligibility for the study was assessed with an in-person interview using the Structured Clinical Interview for DSM-IV Disorders (SCID) (First et al., 1995), self-reported medical history, a series of self-report questionnaires, and physical examinations. All subjects participated voluntarily. In order

Psychiatric and cognitive changes

The 22 men enrolled in the study completed two 3-day admissions at the Clinical Research Center. Their profiles are summarized in Table 1. Mean age was 30.95 ± 4.15 years.

In the between group comparison, subjects who used smartphones with blue light showed significantly decreased sleepiness (Cohen's d = 0.49, Z = 43.50, p = 0.04) and confusion-bewilderment (Cohen's d = 0.53, Z = 39.00, p = 0.02), and increased commission error (Cohen's d = −0.59, t = −2.64, p = 0.02) after smartphone use,

Discussion

This is the first controlled study to investigate the influence of the exposure of blue light from smartphone LED displays at night on humans. The study used newly developed smartphones that suppressed blue light from the LED display, with a screen appearance that was otherwise identical to the conventional blue light LED smartphone. Exposure to the blue light LED display at night decreased user sleepiness and confusion-bewilderment, and increased commission errors. Also, blue light LED

Role of funding source

The sponsors had no role in the analysis of the data, the writing of the report, or the decision to submit the paper for publication.

Contributors

Prof. Hong Jin Jeon was a principal investigator of this study, designed the study, and educated and supervised the interviewers, and checked the whole data. Dr. Jung-Yoon Heo and Dr. Kiwon Kim, Dong Jun Kim, Kyung-Ah Judy Chang, Yunhye Oh, Bum-Hee Yu and Min-Ji Kim wrote the manuscript and analyzed the data. Prof. Maurizio Fava, David Mischoulon, and George I. Papakostas checked the results and supervised the analysis and manuscript.

Disclosure of any conflicts of interest

Dr. Fava has received research support from Abbott Laboratories, Alkermes, Aspect Medical Systems, Astra-Zeneca, BioResearch, BrainCells, Inc., Bristol-Myers Squibb Company, Cephalon, Clinical Trial Solutions, LLC, Eli Lilly & Company, EnVivo Pharmaceuticals, Inc., Forest Pharmaceuticals Inc., Ganeden, GlaxoSmithKline, J & J Pharmaceuticals, Lichtwer Pharma GmbH, Lorex Pharmaceuticals, NARSAD, NCCAM, NIDA, NIMH, Novartis, Organon Inc., PamLab, LLC, Pfizer Inc, Pharmavite, Roche, Sanofi-Aventis,

Acknowledgements

This research was supported by Samsung Display (S-2014-1823-000). This research was also supported by the Original Technology Research Program for Brain Science through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. NRF-2016M3C7A1947307; PI, Hong Jin Jeon), and by a grant of the Korean Mental Health Technology R&D Project, Ministry of Health & Welfare, Republic of Korea (No. HM14C2567) (PI: Hong Jin Jeon). The authors thank the

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