The timing of daytime sleep, and thus the timing of daytime light exposure, affects the size and direction of the phase shift induced by a week of night shifts

Abstract Objective To assess light exposure during days with indoor, outdoor, and night work and days off work. Methods Light intensity was continuously recorded for 7 days across the year among indoor (n = 170), outdoor (n = 151), and night workers (n = 188) in Denmark (55–56°N) equipped with a personal light recorder. White light intensity, duration above 80, 1000, and 2500 lux, and proportion of red, green, and blue light was depicted by time of the day and season for work days and days off work. Results Indoor workers’ average light exposure only intermittently exceeded 1000 lux during daytime working hours in summer and never in winter. During daytime working hours, most outdoor workers exceeded 2500 lux in summer and 1000 lux in winter. Night workers spent on average 10–50 min >80 lux when working night shifts. During days off work, indoor and night workers were exposed to higher light intensities than during work days and few differences were seen between indoor, outdoor, and night workers. The spectral composition of light was similar for indoor, outdoor, and night workers during days at and off work. Conclusion The night workers of this study were during night hours on average exposed for a limited time to light intensities expected to suppress melatonin. The indoor workers were exposed to light levels during daylight hours that may reduce general well-being and mood, especially in winter. Outdoor workers were during summer daylight hours exposed to light levels comparable to those used for the treatment of depression.

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Extraocular Light Exposure Does Not Phase Shift Saliva Melatonin Rhythms in Sleeping Subjects

Journal of Biological Rhythms ◽

10.1177/074873002129002582 ◽

2002 ◽

Vol 17 (4) ◽

pp. 377-386 ◽

Cited By ~ 12

Author(s):

K. Lushington ◽

R. Galka ◽

L. N. Sassi ◽

D. J. Kennaway ◽

D. Dawson

Keyword(s):

Phase Shift ◽

Light Exposure

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Integration of brief light flashes varying in intensity and duration by the human circadian system

10.1101/759134 ◽

2019 ◽

Author(s):

Daniel S. Joyce ◽

Manuel Spitschan ◽

Jamie M. Zeitzer

Keyword(s):

Phase Shift ◽

Light Exposure ◽

Temporal Integration ◽

Circadian System ◽

Flash Intensity ◽

Flash Duration ◽

Variable Intensity ◽

Circadian Phase ◽

Variable Duration ◽

Circadian Phase Shift

AbstractThe human circadian system is exquisitely sensitive to light, through a pathway connecting the melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs) to the hypothalamic suprachiasmatic nuclei (SCN). ipRGCs are characterised by a delayed off-time following cessation of light exposure; we exploited this unusual physiologic property and examined how a sequence of flashes of bright light differing in intensity or duration presented in the biological night could delay the human circadian clock in vivo in healthy young participants (n=54). To understand the mechanism underlying circadian photoreception, we probed temporal integration by manipulating flash intensity and duration independently. In a 34-hour in-laboratory between-subjects design, we examined variable-intensity (3, 30, 95, 300, 950, 3000, or 9500 photopic lux; n=28 participants) flashes at fixed duration (2 ms), and variable-duration (10 μs, 100 μs, 1 ms, 10 ms, 100 ms, 1 sec, 10 sec) flashes at fixed intensity (2000 photopic lux; n=31 participants). We measured the phase shift of dim-light melatonin onset on the subsequent evening, and acute melatonin suppression and alertness during the flash sequence. In the variable-intensity study, we find a clear sigmoidal dose-response relationship for flash intensity and the induced circadian phase shift. In the variable-duration study, we find no parametric relationship between flash duration and induced circadian phase shift, indicating a relative insensitivity of the circadian system to flashes varying in duration. As the intermittent periods of darkness in our stimulation paradigm supports the recovery of extrinsic rod-cone signalling into the ipRGCs, our results strongly suggest rod-cone contributions into circadian photoreception.

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156 Evening Light-Induced Circadian Phase Shift in Preschool-Aged Children

SLEEP ◽

10.1093/sleep/zsab072.155 ◽

2021 ◽

Vol 44 (Supplement_2) ◽

pp. A63-A64

Author(s):

Lauren Hartstein ◽

Lameese Akacem ◽

Cecilia Diniz Behn ◽

Shelby Stowe ◽

Kenneth Wright ◽

...

Keyword(s):

Phase Shift ◽

Light Exposure ◽

Light Stimulus ◽

Phase Delay ◽

Healthy Children ◽

Dependent Manner ◽

Circadian Phase ◽

Light Intensities ◽

Dim Light ◽

Dose Dependent

Abstract Introduction In adults, exposure to light at night delays the timing of the circadian clock in a dose-dependent manner with intensity. Although children’s melatonin levels are highly suppressed by evening bright light, the sensitivity of young children’s circadian timing to evening light is unknown. This research aimed to establish an illuminance response curve for phase delay in preschool children as a result of exposure to varying light intensities in the hour before bedtime. Methods Healthy children (n=36, 3.0 – 4.9 years, 39% males), participated in a 10-day protocol. For 7 days, children followed a strict parent-selected sleep schedule. On Days 8-10, an in-home dim-light assessment was performed. On Day 8, dim light melatonin onset (DLMO) was measured through saliva samples collected in 20-30-min intervals throughout the evening until 1-h past habitual bedtime. On Day 9, children were exposed to a white light stimulus (semi-randomly assigned from 5lx to 5000lx) for 1-h before their habitual bedtime, and saliva was collected before, during, and after the exposure. On Day 10, children provided saliva samples in the evening for 2.5-h past bedtime for a final DLMO assessment. Phase angle of entrainment (habitual bedtime – DLMObaseline) and circadian phase delay (DLMOfinal – DLMObaseline) were computed. Results Final DLMO (Day 10) shifted between -8 and 123 minutes (M = 56.1 +/- 33.6 min; negative value = phase advance, positive value = phase delay) compared with DLMO at baseline (Day 8). Raw phase shift did not demonstrate a dose-dependent relationship with light intensity. Rather, we observed a robust phase delay across all intensities. Conclusion These data suggest preschoolers’ circadian clocks are immensely sensitive to a large range of light intensities, which may be mechanistically influenced by less mature ophthalmologic features (e.g. clearer lenses, larger pupils). With young children’s ever-growing use of light-emitting devices and evening exposure to artificial lighting, as well as the prevalence of behavioral sleep problems, these findings may inform recommendations for parents on the effects of evening light exposure on sleep timing in early childhood. Support (if any) This research was supported with funds from the Eunice Kennedy Shriver National Institute of Child Health & Human Development (R01-HD087707).

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Visual impairment and circadian rhythm disorders

Dialogues in Clinical Neuroscience ◽

10.31887/dcns.2007.9.3/slockley ◽

2007 ◽

Vol 9 (3) ◽

pp. 301-314 ◽

Cited By ~ 8

Keyword(s):

Circadian Rhythms ◽

Light Exposure ◽

Well Being ◽

Poor Sleep ◽

Melatonin Administration ◽

Treatment Dose ◽

Performance Patterns ◽

And Performance ◽

And Behavior ◽

Night Shifts

Many aspects of human physiology and behavior are dominated by 24-hour circadian rhythms that have a major impact on our health and well-being, including the sleep-wake cycle, alertness and performance patterns, and many daily hormone profiles. These rhythms are spontaneously generated by an internal "pacemaker" in the hypothalamus, and daily light exposure to the eyes is required to keep these circadian rhythms synchronized both internally and with the external environment. Sighted individuals take this daily synchronization process for granted, although they experience some of the consequences of circadian desynchrony when "jetlagged" or working night shifts. Most blind people with no perception of light, however, experience continual circadian desynchrony through a failure of light information to reach the hypothalamic circadian clock, resulting in cyclical episodes of poor sleep and daytime dysfunction. Daily melatonin administration, which provides a replacement synchronizing daily "time cue, " is a promising therapeutic strategy, although optimal treatment dose and timing remain to be determined.

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Daytime naps in darkness phase shift the human circadian rhythms of melatonin and thyrotropin secretion

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.2000.278.2.r373 ◽

2000 ◽

Vol 278 (2) ◽

pp. R373-R382 ◽

Cited By ~ 35

Author(s):

Orfeu M. Buxton ◽

Mireille L'Hermite-Balériaux ◽

Fred W. Turek ◽

Eve van Cauter

Keyword(s):

Circadian Rhythms ◽

Phase Shift ◽

Light Exposure ◽

Caloric Intake ◽

Stimulus Exposure ◽

Blood Samples ◽

Circadian Misalignment ◽

Circadian Phase ◽

Before And After ◽

Dim Light

To systematically determine the effects of daytime exposure to sleep in darkness on human circadian phase, four groups of subjects participated in 4-day studies involving either no nap (control), a morning nap (0900–1500), an afternoon nap (1400–2000), or an evening nap (1900–0100) in darkness. Except during the scheduled sleep/dark periods, subjects remained awake under constant conditions, i.e., constant dim light exposure (36 lx), recumbence, and caloric intake. Blood samples were collected at 20-min intervals for 64 h to determine the onsets of nocturnal melatonin and thyrotropin secretion as markers of circadian phase before and after stimulus exposure. Sleep was polygraphically recorded. Exposure to sleep and darkness in the morning resulted in phase delays, whereas exposure in the evening resulted in phase advances relative to controls. Afternoon naps did not change circadian phase. These findings indicate that human circadian phase is dependent on the timing of darkness and/or sleep exposure and that strategies to treat circadian misalignment should consider not only the timing and intensity of light, but also the timing of darkness and/or sleep.

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0777 Variations in Vigilance and Sleep Among Underground Mine Workers During 14 Consecutive Night Shifts

SLEEP ◽

10.1093/sleep/zsaa056.773 ◽

2020 ◽

Vol 43 (Supplement_1) ◽

pp. A295-A296

Author(s):

L Laberge ◽

A A Lavigne ◽

J Auclair ◽

M Hébert

Keyword(s):

Older Workers ◽

Repeated Measures ◽

Light Exposure ◽

Night Shift ◽

Consecutive Night ◽

Linear Regression Models ◽

Engineering Research ◽

Partial Sleep Deprivation ◽

Night Shifts ◽

Mine Workers

Abstract Introduction Adverse effects of night shift work are well known but there is scarce data on how vigilance and sleep vary across a large number of consecutive night shifts. Methods In summer, 38 underground miners (mean age (SD): 36.8 (13.9) years) wore an actigraph, filled out the Morningness-Eveningness questionnaire, and completed a Visual Analog Scale capturing subjective vigilance (very sleepy to very alert) 4 times per shift (19:00, 22:00, 02:00, and 05:30) for 14 consecutive night shifts. Mixed effects linear regression models were used to account for repeated measures. Results Mean vigilance level is lower at 22:00, 02:00 and 05:30 than at the beginning of the shift at 19:00 (p<0.001). Also, a more pronounced decrease in vigilance during the night was observed among older workers compared to younger workers (p<0.05). Moreover, workers with greater eveningness have higher vigilance at the beginning of the first night shift at 19:00 (p<0.001), but their decline in vigilance level during the night is faster than that observed in workers with greater morningness (p<0.01). Interestingly, the mean vigilance decline observed at 02:00 and 05:30 (compared to 19:00) is slowed down for each additional night shift (p<0.001). Furthermore, mean sleep efficiency is negatively associated with morningness and gradually decreases across consecutive night shifts (p<0.05). In addition, mean sleep duration is shorter in older workers and is positively associated with morningness (p<0.05). Conclusion Results show a progressive improvement in vigilance of mine workers assigned to a large number of consecutive 12-hour night shifts from 2 am onwards. This may probably be ascribed to an adjustment in homeostatic sleep propensity consecutive to the partial sleep deprivation associated with time spent traveling to the remote site before the first shift. However, circadian adjustment is unlikely considering the strong morning light exposure experienced daily after the night shift. Support College and Community Innovation Program of the Natural Sciences and Engineering Research Council of Canada (NSERC) (CUI2I 472201-14)

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