Circadian Entrainment & Zeitgebers — References

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Parent Topic: Circadian Entrainment & Zeitgebers | References Hub: 01 - Foundations References MOC

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Primary Literature & Landmark Studies

Gooley et al. (2011)

• Citation: Gooley, J. J., Chamberlain, K., Smith, K. A., Khalsa, S. B., Rajaratnam, S. M., Van Reen, E., Zeitzer, J. M., Czeisler, C. A., & Lockley, S. W. (2011). Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humans. The Journal of Clinical Endocrinology & Metabolism, 96(3), E463–E472.
• Identifiers: DOI: 10.1210/jc.2010-2098 (DOI · SciDB · Scholar) | PMID: 21193540 (PubMed · Europe PMC)
• Study Design: Inpatient laboratory crossover study in healthy adults ($N=116$, aged 18–30 years) comparing room light (<200 lux) vs. dim light (<3 lux) for 8 hours preceding bedtime.
• Key Quantitative Outcomes:
  • Pre-bedtime room light suppressed melatonin onset in 99.0% (93 of 94) of individuals and shortened the total duration of nocturnal melatonin secretion by ~90 minutes ($p<0.0001$).
  • Exposure to room light during usual sleep hours suppressed total plasma melatonin area under the curve (AUC) by >50% in 85% of trials.

Chang et al. (2015)

• Citation: Chang, A. M., Aeschbach, D., Duffy, J. F., & Czeisler, C. A. (2015). Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences (PNAS), 112(4), 1232–1237.
• Identifiers: DOI: 10.1073/pnas.1418490112 (DOI · SciDB · Scholar) | PMID: 25535358 (PubMed · Europe PMC)
• Study Design: 14-day inpatient randomized crossover trial in healthy adults ($N=12$; 5 consecutive evenings of reading an iPad/light-emitting eReader vs. 5 evenings reading a printed book under reflected light for 4 hours pre-bed).
• Key Quantitative Outcomes:
  • Light-emitting eReader use suppressed evening melatonin levels by 55.12 ± 20.12% (vs. $-18.77\pm 39.57\%$ with printed books; $p<0.001$).
  • Dim-Light Melatonin Onset (DLMO) was delayed by 1.5 hours ($p<0.0001$), sleep onset latency increased by ~10 minutes, total REM sleep decreased, and next-morning alertness was significantly impaired.

Brown et al. (2022)

• Citation: Brown, T. M., Brainard, G. C., Cajochen, C., Czeisler, C. A., Hanifin, J. P., Lockley, S. W., Lucas, R. J., Münch, M., O’Hagan, J. B., Peirson, S. N., Price, L. L. A., Roenneberg, T., Schlangen, L. J. M., Skene, D. J., Spitschan, M., Vetter, C., Zee, P. C., & Wright, K. P. Jr. (2022). Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults. PLOS Biology, 20(3), e3001571.
• Identifiers: DOI: 10.1371/journal.pbio.3001571 (DOI · SciDB · Scholar) | PMID: 35298459 (PubMed · Europe PMC)
• Study Design: International consensus panel synthesis and quantitative photobiological modeling across human circadian, neuroendocrine, and alerting responses.
• Key Quantitative Outcomes:
  • Established standardized melanopic Equivalent Daylight Illuminance (mEDI) measured at the eye (vertical plane, 1.2 m height):
    • Daytime: Minimum $\ge 250$ lux mEDI throughout the day.
    • Evening (starting $\ge 3$ h before bedtime): Maximum $\le 10$ lux mEDI.
    • Nighttime (sleep environment): Maximum $\le 1$ lux mEDI.

Stothard et al. (2017)

• Citation: Stothard, E. R., McHill, A. W., Depner, C. M., Birks, B. R., Moehlman, T. M., Ritchie, H. K., Guzzetti, J. R., Chinoy, E. D., LeBourgeois, M. K., Axelsson, J., & Wright, K. P. Jr. (2017). Circadian entrainment to the natural light-dark cycle across seasons and the weekend. Current Biology, 27(4), 508–513.
• Identifiers: DOI: 10.1016/j.cub.2016.12.041 (DOI · SciDB · Scholar) | PMID: 28162893 (PubMed · Europe PMC)
• Study Design: Controlled field intervention study in healthy adults ($N=14$ winter camping study; $N=14$ weekend camping vs. home environment comparison).
• Key Quantitative Outcomes:
  • Winter campers exposed solely to natural sunlight (13× higher daytime light exposure than modern indoor environments) advanced their melatonin onset by 2.6 hours ($p<0.0001$).
  • A single weekend of natural light exposure advanced circadian phase by 1.4 hours ($p<0.005$) and prevented the typical weekend circadian delay (“social jetlag”).