Evning Exposure to Computer Screen Disrupts Sleep, Attention and Biological Rhythms
Condition: Sleep Disorder
MeSH terms: Sleep Wake Disorders
Study type: Interventional

Summary: 
      Light exposure is on the rise in recent years. In large part because of unintentional
      illumination from screens that emit light directly into the eyes. Millions of computers,
      tablets, televisions, and smart-phones are sold worldwide every month and the usage time of
      these devices is increasing constantly. Today, people are exposed to ongoing light exposure
      from these device screens, emitting short wave length (SWL) during day and night hours,
      whether as active or passive users. In sum, artificial light at night (ALAN) seem to affect
      human circadian rhythmicity (melatonin and thermoregulation) and sleep, with two major
      factors. First, wavelength of light, with SWL being most detrimental to sleep and rhythms,
      when compared to LWL (Brianard et al., 2001). Second, a dose-response relationship exists
      between increasing light intensity and poorer sleep/circadian rhythms (Brianard et al., 1988;
      West et al., 2011).

      Based on existing knowledge, we hypothesize that when compared to long wavelength LWL
      illumination, short wavelength SWL illumination from computer screen will have a more
      damaging effect on melatonin (MLT) production and secretion, interfering body temperature
      regulation and affecting sleep quality, efficiency and sleep architecture. In addition, we
      hypothesized that intensity of the screen illumination will play another important factor on
      these outcomes, we assume that high intensity compared to low intensity will have more
      damaging effect on: melatonin, thermoregulation and sleep.
    

Detailed description: 
      Methods:

      Participants Participants were between the ages of 20 and 45 years, with BMI 18-25, regular
      sleep habits in Pittsburgh Sleep Quality Index (PSQI) questionnaire index<5 (Buysse et al.,
      1989, Shochat et al., 2007), and a normative sleep-wake cycle type (Horne-Ostberg
      morningness-eveningness questionnaire (Horne & Ostberg, 1976, Lavie & Segal, 1990) measured
      Sleep quality and continuity were measured for one week using actigraphy with compatible
      decoding software (Respironics Model II, Philips, Inc). Only participants with 6-8 hours of
      sleep, normative sleep patterns, and no sleep/wake schedule problems proceeded to the
      experimental phase of the study stage. Participants were healthy with no history of medical,
      neurological, sleep disorders (confirmed by polysomnography) or psychiatric conditions and no
      medication intake (excluding contraceptives for female participants). Participants with
      ocular damage, such as to their field of vision, color blindness, or impaired functioning of
      the pupil in reaction to light were excluded, however use of eyeglasses or contact lenses to
      correct vision was allowed. Participants signed informed consent prior to participation in
      the study. The study was approved by the Helsinki Committee of Assuta Medical Center and
      Maccabi Health Services.

      Measurements

      Three physiological measures were collected in the study:

      Polysomnography: The sleep testing room was a standard test room at the Sleep Medicine
      Research Center at Assuta Medical Center. Standard in-lab polysomnography was conducted using
      the Somnoscreen-polysomnography (PSG) type sleeping test instrument (Somnomedics, Germany).
      Sleep channels included: electroencephalography (EEG), electro-oculography (EOG), leg and
      chin electromyography (EMG), nasal breathing, chest breathing, diaphragm breath, snoring,
      electro-cardio-graphy (EKG), heart rate, blood oxygen saturation, and body position. Sleep
      data processing was performed by skilled and trained sleep technicians in accordance with of
      the Rechtschaffen and Kales criteria (1968). Sleep continuity parameters: latency to stage 1
      (SL1) and stage 2 (SL2), percent wake after sleep onset (%WASO), index of awakenings, total
      sleep time (TST), time in bed (TIB), and sleep efficiency (SE). Sleep architecture
      parameters: percent stage 1 (%S1), stage 2 (%S2), REM (%REM), and SWS (%SWS), index of sleep
      stage changes and REM onset latency (ROL).

      Melatonin: Urine samples were collected for analyzing melatonin levels by measuring
      6-sulfahydroxymelatonin (6-SMT) concentration, the major metabolite of the hormone in urine
      (de Almeida et al., 2011). The quantitative determination of 6-SMT in urine was completed by
      a solid phase enzyme-linked immunosorbent assay (ELISA # RE54031; IBL, Hamburg; Germany) as
      described previously (Zubidat & Haim, 2007). 6-SMT concentrations (ng/mL) were
      spectrophotometrically determined by ELISA microplate reader at 450 nm with reference
      wavelength 650 nm (PowerWave HT, Biotek, Winooski; USA) and analyzed by Gen5TM Data Analysis
      Software (Version 2, Biotek, Winooski; USA).

      Urine samples were collected on all four days of the experiment at three time points: 21:00,
      23:00 and at wake time. All urine samples were frozen (-20OC) immediately after collection.
      Melatonin was then analyses and secretion parameters were estimated. As the first morning
      sample concentration of 6-SMT has been extensively used as an estimate of overnight melatonin
      secretion (McMullan et al., 2013), we used this sample to represent the maximum (100%) MLT
      secretion per participant. The night samples (at 21:00 and 23:00) were transformed using the
      formula value at 21:00 or 23:00 /value in wake time *100 to reflect the percentage change in
      MLT secretion per participant.

      Temperature: Oral temperature was measured using an electronic oral thermometer (Domotherem,
      UEBE Medical GMBH, Germany).

      Procedure:

      Recruitment ads were placed in social network websites stating basic inclusion criteria and
      study details. Interested persons were initially interviewed via phone to rule out major
      exclusion criteria (e.g. age, general health, and sleep patterns). Persons who were eligible
      and interested in participating were invited to the sleep laboratory at Assuta Medical Center
      (Tel Aviva, Israel) for in-lab screening. At the screening visit, all participants signed
      informed of consent and filled out intake questionnaires, including demographic and health
      questionnaires, PSQI, and the Horne-Ostberg questionnaire). Participants then received an
      actigraph for one week to assess the quality and quantity of their sleep and sleep wake
      patterns and schedules.

      Following the home screening, participants were scheduled for four in-lab testing nights
      across two consecutive weeks. Participants were always scheduled on Sunday and Wednesday
      nights for each week. For the duration of the 2-week experimental period, all participants
      were requested to sleep in accordance with their normal sleep schedule, both at home and at
      the laboratory.

      A repeated measures design was used, with two independent variables: screen luminance (or
      light intensity emitted from the screen) and light wavelength. The first, luminance at two
      levels: low - 80 lux (35mw/cm2) and high - 350 lux (160mw/cm2). The second, wavelength at two
      levels: short (SWL)-485 nm (13500k) and long (LWL)-620 nm (4250k). Luminance and wavelength
      levels were measured and adjusted using a light metering device (AvaSpec-2048-FT-SDU;
      Avantes, Inc., Eerbeek, Netherlands). There were three dependent measures that were analyzed
      separately, sleep, melatonin secretion, and oral temperature. Each participant underwent all
      four experimental conditions in counterbalanced order.

      Participants arrived at sleep laboratory at 21:00h on all experimental nights. The experiment
      room was about 12 m2 in size and included a desk with a 22-inch computer LED (Light Emitting
      Diode) screen (Model 226V4L, Philips, USA) and a bed. The screen was placed at a distance of
      about 60 cm from the participant and at eye level.

      The room was dark and the room temperature was set to 22OC. Participants sat in front of the
      computer screen for two hours and performed onscreen tasks between 21:00h and 23:00h. Tasks
      were reading texts and answering related questions, writing exercises and solving verbal and
      arithmetic problems. Participants were not informed of the differing light conditions and
      were told that the purpose of the study is to examine the effect of the content of the tasks
      on sleep.

      During exposure, the subjects were allowed to eat light food and drink (non-caffeinated
      beverages only). Participants were requested to go to the bathroom before testing and were
      not allowed leave the room for the duration of the testing. Following the light exposure,
      participants were connected to the sleep testing system by a skilled technician and requested
      to go to sleep. Bedtimes and wake times were based on the average sleep/wake time as
      indicated in the individual actigraphy reports. Oral temperature was taken at six time
      points, three on the testing night: 21:00h, 23:00h, and immediately prior to bedtime and at
      three the following morning, at 0, 60, and 120 minutes after awakening. Urine samples were
      collected at three time points: 21:00h, 23:00h, and immediately following morning awakening.
      This protocol was repeated for each of the four testing nights. Upon completion of the study
      protocol participants were given monetary compensation for their participation in the study.

      Statistical analysis:

      Two-way (wavelength X intensity) repeated measures (RM) ANOVAs were performed to evaluate
      mean value differences for all sleep parameters. Three-way (wavelength x intensity X time) RM
      ANOVAs were performed to evaluate mean value differences in melatonin and temperature
      indices. Post-hoc Tukey tests were performed for significant ANOVAs. Two-tailed p-values
      below 0.05 were considered significant. Statistical analyses were preformed using SPSS,
      version 20 (SPSS Inc., Chicago, IL, USA).
    

Intervention name(s): Wavelength; Intensity
Intervention type(s): Other; Other
Intervention description(s): wavelength at two levels: short (SWL)-485 nm (13500k) and long (LWL)-620 nm (4250k); Luminance at two levels: low - 80 lux (35mw/cm2) and high - 350 lux (160mw/cm2
Allocation: Randomized
Intervention model: Factorial Assignment
Masking: Single (Participant)
Primary purpose: Basic Science
Keywords: Sleep, Melatonin; Circadian Rhythm; Temperature; screen illumination