Diurnal variations of hormonal secretion, alertness and cognition in extreme chronotypes under different lighting conditions (original) (raw)
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The impact of daytime light exposures on sleep and mood in office workers
Sleep Health, 2017
Background: By affecting the internal timing mechanisms of the brain, light regulates human physiology and behavior, perhaps most notably the sleep-wake cycle. Humans spend over 90% of their waking hours indoors, yet light in the built environment is not designed to affect circadian rhythms. Objective: Using a device calibrated to measure light that is effective for the circadian system (circadianeffective light), collect personal light exposures in office workers and relate them to their sleep and mood. Setting: The research was conducted in 5 buildings managed by the US General Services Administration. Participants: This study recruited 109 participants (69 females), of whom 81 (54 females) participated in both winter and summer. Measurements: Self-reported measures of mood and sleep, and objective measures of circadian-effective light and activity rhythms were collected for 7 consecutive days. Results: Compared to office workers receiving low levels of circadian-effective light in the morning, receiving high levels in the morning is associated with reduced sleep onset latency (especially in winter), increased phasor magnitudes (a measure of circadian entrainment), and increased sleep quality. High levels of circadian-effective light during the entire day are also associated with increased phasor magnitudes, reduced depression, and increased sleep quality. Conclusions: The present study is the first to measure personal light exposures in office workers using a calibrated device that measures circadian-effective light and relate those light measures to mood, stress, and sleep. The study's results underscore the importance of daytime light exposures for sleep health.
Journal of Pineal Research, 1994
Different patterns of light exposure in relation to melatonin and cortisol rhythms and sleep of night workers. J. Pineal Res. 1994:16:127-135. Abstract: There is strong evidence to suggest that circadian psychophysiological adaptation processes are modified by light, depending on its intensity and timing. To characterize such modifications and determine whether they are associated with an alteration in the dayhight pattern of melatonin excretion, measurements were obtained around the clock in 14 permanent night workers, each studied over a 48 hr period in the field. The light exposure behavior of these workers was studied with a newly developed light dosimetry by measuring light intensity at eye level. Physical activity was continuously registered and sleep indices were obtained by sleep logs and activity markings. Circadian rhythms of melatonin and cortisol were analysed from salivary samples collected for 24 hr at 2 hr intervals. The interindividual variation of melatonin acrophase determined by cosinor analysis was greater than 180 degrees (from around midnight to noon) and that of cortisol was about 135 degrees (from early morning to afternoon). Hormonal phase positions coincided significantly with light exposure: the more bright light pulses in the morning (maximum lux between 0600 and 0900), the less were the melatonin and cortisol acrophases shifted into the day. There was also a negative correlation between melatonin acrophase shift and duration of the overall light exposure above 1500 lux. Morning light maximum and sleep onset correlated highly significantly. Night workers were divided into those with less than ('non-shifters', n = 9) and more than 6 hr deviation from midnight ('shifters', n = 5) of the melatonin acrophase. The group comparison revealed a marked difference of the mean melatonin concentrations at night, and at 0700. Shifters did not experience bright light exposure in the morning and showed a tendency towards shorter overall exposure of light above 1500 lux. In conclusion, light avoidance behavior during morning hours, as observed in 5 out of 14 night workers, coincided significantly with a phase delay of melatonin acrophase. Light avoidance also correlated with an earlier sleep onset and a tendency to longer sleep hours. Thus our data suggest that the interaction of a phase shifted activity cycle and the lighvdark exposure leads in the field situation to different degrees of adaptation to the prevailing activitykest requirements, depending on dose and phase position of bright light exposure.
Cancer Epidemiology, Biomarkers & Prevention, 2014
Background: Light-at-night has been shown in experimental studies to disrupt melatonin production but this has only partly been confirmed in studies of night shift workers. In this cross-sectional study, we examined the circadian variation of melatonin in relation to shift status, individual levels of light-at-night exposure, and diurnal preference, an attribute reflecting personal preference for activity in the morning or evening. Methods: One hundred and seventeen workers (75 night and 42 day) of both sexes, ages 22 to 64 years, were recruited from four companies. Participants collected urine samples from all voids over 24 hours and wore a data logger continuously recording their light exposure. Sociodemographic, occupational, lifestyle, and diurnal preference information were collected by interview. Concentrations of urinary 6-sulfatoxymelatonin (aMT6s), the main melatonin metabolite, were measured. Results: Mean aMT6s levels were lower in night [10.9 ng/mg creatinine/hour; 95% c...
Circadian-effective light and its impact on alertness in office workers
Lighting Research & Technology, 2018
A field study was conducted at two U.S. federal government office sites and two U.S. embassies to demonstrate whether circadian-effective lighting (providing circadian stimulus (CS) values of CS ≥ 0.3) could be installed in office buildings, and to determine whether this lighting intervention would reduce sleepiness and increase alertness, vitality and energy in office workers while at work. Desktop and/or overhead luminaires provided circadian-effective lighting at participants’ eyes during a two-day intervention. A pendant-mounted Daysimeter device was used to measure participant-specific CS values during the baseline and the intervention days. Participants also completed questionnaires inquiring about sleep habits, stress and subjective feelings of vitality and energy. The Daysimeter data showed that participants were exposed to significantly higher amounts of circadian-effective light while at work during the two intervention days compared to the baseline day. Self-reported slee...
Nocturnal white light exposure has shown marked results on subjective and objective indicators of alertness, vitality and mood, yet effects of white light during daytime and under usual office work conditions have not been investigated extensively. The current study employed a mixed-group design (N = 32), testing effects of two illuminance levels (200 lx or 1000 lx at eye level, 4000 K) during one hour of morning versus afternoon exposure. In four repeated blocks, subjective reports, objective performance and physiological arousal were measured. Results showed effects of illuminance on subjective alertness and vitality, sustained attention in tasks, and heart rate and heart rate variability. Participants felt less sleepy and more energetic in the high versus the low lighting condition, had shorter reaction times on the psychomotor vigilance task and increased physiological arousal. Effects of illuminance on the subjective measures, as well as those on heart rate were not dependent on time of day or duration of exposure. Performance effects were most pronounced in the morning sessions and towards the end of the one-hour exposure period. The effect on heart rate variability was also most pronounced at the end of the one-hour exposure. The results demonstrate that even under normal, i.e., neither sleep nor light deprived conditions, more intense light can improve feelings of alertness and vitality, as well as objective performance and physiological arousal.
International journal of occupational safety and ergonomics : JOSE, 2010
In this study, the effects of bright light (BL) on the rhythms in body temperature, plasma melatonin, plasma cortisol and subjective alertness, in 34 shift work nurses at a university hospital were assessed. They were exposed to very BL (4,500 lx) during 2 breaks (21:15-22:00 and 3:15-4:00) or dim light (300 lx). The subjects were studied under 24 h of realistic conditions during which their plasma cortisol and melatonin were measured at 3-h intervals; their body temperature was also measured during and after night shift work. Subjective alertness was evaluated with the Karolinska sleepiness scale. Administration of BL significantly suppressed night-time melatonin levels. A one-way ANOVA revealed that BL tended to increase cortisol levels and body temperature and significantly improved alertness. These results demonstrate that photic stimulation in a hospital setting can have a powerful influence on the adjustment of the circadian system.
Daylight in Office Buildings: Impact of Building Design on Personal Light Exposures, Sleep and Mood*
2015
Lighting design for office buildings has focused largely on the amount of light for visibility, strategies to reduce visual discomfort, and the use of daylight as a means to reduce energy in buildings. Little attention has been given to understanding how light affects occupants’ psychological and physiological systems, including circadian functions that regulate sleep, mood, and alertness. The specific goals of the present study were to: (1) perform photometric measurements at workstations in winter and late spring, and (2) analyze the impacts of personal light exposure on circadian entrainment using a wearable light and activity measurement device. Reported here are the results of the measurements performed during two seasons in a building located in the Northwest region of the United States.