title: Effects of a chronic reduction of short-wavelength light input on melatonin and sleep patterns in humans: evidence for adaptation.
abstract: Light is an important environmental stimulus for the entrainment of the circadian clock and for increasing alertness. The intrinsically photosensitive ganglion cells in the retina play an important role in transferring this light information to the circadian system and they are elicited in particular by short-wavelength light. Exposure to short wavelengths is reduced, for instance, in elderly people due to yellowing of the ocular lenses. This reduction may be involved in the disrupted circadian rhythms observed in aged subjects. Here, we tested the effects of reduced blue light exposure in young healthy subjects (n = 15) by using soft orange contact lenses (SOCL). We showed (as expected) that a reduction in the melatonin suppressing effect of light is observed when subjects wear the SOCL. However, after chronic exposure to reduced (short wavelength) light for two consecutive weeks we observed an increase in sensitivity of the melatonin suppression response. The response normalized as if it took place under a polychromatic light pulse. No differences were found in the dim light melatonin onset or in the amplitude of the melatonin rhythms after chronic reduced blue light exposure. The effects on sleep parameters were limited. Our results demonstrate that the non-visual light system of healthy young subjects is capable of adapting to changes in the spectral composition of environmental light exposure. The present results emphasize the importance of considering not only the short-term effects of changes in environmental light characteristics.
authors.affiliation: Research Unit of Chronobiology, Center for Life Sciences, University of Groningen , Groningen , The Netherlands .
authors.forename: Marina C
authors.initials: MC
authors.lastname: Giménez
authors.forename: Domien G M
authors.initials: DG
authors.lastname: Beersma
authors.forename: Pauline
authors.initials: P
authors.lastname: Bollen
authors.forename: Matthijs L
authors.initials: ML
authors.lastname: van der Linden
authors.forename: Marijke C M
authors.initials: MC
authors.lastname: Gordijn
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D015415:Biomarkers / Q000378:metabolism; D002940:Circadian Rhythm / Q000528:radiation effects*; D003263:Contact Lenses, Hydrophilic; D005260:Female; D006801:Humans; D008027:Light; D055537:Light Signal Transduction / Q000528:radiation effects; D008297:Male; D008550:Melatonin / Q000378:metabolism*; D009426:Netherlands; D017440:Photoperiod; D012165:Retinal Ganglion Cells / Q000502:physiology / Q000528:radiation effects*; D012463:Saliva / Q000378:metabolism*; D012890:Sleep / Q000528:radiation effects*; D013997:Time Factors; D055815:Young Adult
chemical_list: D015415:Biomarkers; D008550:Melatonin
keywords: Adaptation; human; melatonin rhythms; short-wavelength light; sleep rhythms