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High sensitivity and interindividual variability in the response of the human circadian system to evening light

Phillips, A.J.K., Vidafar, P., Burns, A.C., McGlashan, E.M., Anderson, C., Rajaratnam, S.M.W., Lockley, S.W. and Cain, S.W. (2019) High sensitivity and interindividual variability in the response of the human circadian system to evening light Proceedings of the National Academy of Sciences of the United States of America, 116 (24). pp. 12019-12024.

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Before the invention of electric lighting, humans were primarily exposed to intense (>300 lux) or dim (<30 lux) environmental light�stimuli at extreme ends of the circadian system�s dose�response curve to light. Today, humans spend hours per day exposed to intermediate light intensities (30�300 lux), particularly in the evening. Interindividual differences in sensitivity to evening light in this intensity range could therefore represent a source of vulnerability to circadian disruption by modern lighting. We characterized individual-level dose�response curves to light-induced melatonin suppression using a within-subjects protocol. Fifty-five participants (aged 18�30) were exposed to a dim control (<1 lux) and a range of experimental light levels (10�2,000 lux for 5 h) in the evening. Melatonin suppression was determined for each light level, and the effective dose for 50% suppression (ED50) was computed at individual and group levels. The group-level fitted ED50 was 24.60 lux, indicating that the circadian system is highly sensitive to evening light at typical indoor levels. Light intensities of 10, 30, and 50 lux resulted in later apparent melatonin onsets by 22, 77, and 109 min, respectively. Individual-level ED50 values ranged by over an order of magnitude (6 lux in the most sensitive individual, 350 lux in the least sensitive individual), with a 26% coefficient of variation. These findings demonstrate that the same evening-light environment is registered by the circadian system very differently between individuals. This interindividual variability may be an important factor for determining the circadian clock�s role in human health and disease. © 2019 National Academy of Sciences. All rights reserved.

Item Type: Article
Authors :
Phillips, A.J.K.
Vidafar, P.
Burns, A.C.
McGlashan, E.M.
Anderson, C.
Rajaratnam, S.M.W.
Cain, S.W.
Date : 2019
DOI : 10.1073/pnas.1901824116
Uncontrolled Keywords : Circadian disruption, Circadian rhythms, Evening light, Light sensitivity, Melatonin suppression, melatonin, melatonin, adult, Article, circadian rhythm, controlled study, female, human, human experiment, individuality, light dark cycle, light exposure, light intensity, male, normal human, photoreactivity, priority journal, stimulus response, young adult, circadian rhythm, illumination, individuality, light, metabolism, physiology, procedures, Adult, Circadian Clocks, Circadian Rhythm, Female, Humans, Individuality, Light, Lighting, Male, Melatonin, Young Adult
Depositing User : Clive Harris
Date Deposited : 17 Jun 2020 00:39
Last Modified : 17 Jun 2020 00:39

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