Early evening light mitigates sleep compromising physiological and alerting responses to subsequent late evening light

Marije te Kulve,Luc J. M. Schlangen,Wouter D. van Marken Lichtenbelt

doi:10.1038/s41598-019-52352-w

Marije te Kulve, Luc J. M. Schlangen + Show 1 more

Open Access

https://doi.org/10.1038/s41598-019-52352-w

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Abstract

The widespread use of electric light and electronic devices has resulted in an excessive exposure to light during the late-evening and at night. This late light exposure acutely suppresses melatonin and sleepiness and delays the circadian clock. Here we investigate whether the acute effects of late-evening light exposure on our physiology and sleepiness are reduced when this light exposure is preceded by early evening bright light. Twelve healthy young females were included in a randomised crossover study. All participants underwent three evening (18:30-00:30) sessions during which melatonin, subjective sleepiness, body temperature and skin blood flow were measured under different light conditions: (A) dim light, (B) dim light with a late-evening (22:30-23:30) light exposure of 750 lx, 4000 K, and (C) the same late-evening light exposure, but now preceded by early-evening bright light exposure (18.30-21.00; 1200 lx, 4000 K). Late-evening light exposure reduced melatonin levels and subjective sleepiness and resulted in larger skin temperature gradients as compared to dim. Interestingly, these effects were reduced when the late-evening light was preceded by an early evening 2.5-hour bright light exposure. Thus daytime and early-evening exposure to bright light can mitigate some of the sleep-disruptive consequences of light exposure in the later evening.

Highlights

The widespread use of electric light and electronic devices has resulted in an excessive exposure to light during the late-evening and at night
All participants underwent three evening (18:30-00:30) sessions during which melatonin, subjective sleepiness, body temperature and skin blood flow were measured under different light conditions: (A) dim light, (B) dim light with a late-evening (22:30-23:30) light exposure of 750 lx, 4000 K, and (C) the same late-evening light exposure, but preceded by early-evening bright light exposure (18.30-21.00; 1200 lx, 4000 K)
The time of melatonin onset under dim light (DLMO) and the time of the minimum core body temperature (CBT) are important commonly used markers of the circadian clock[4].Misalignment between the biological clock and behavioural rhythms induces sleep disturbances and daytime sleepiness, but can result in desynchronization of internal rhythms[5]

Summary

Introduction

The widespread use of electric light and electronic devices has resulted in an excessive exposure to light during the late-evening and at night. Night-time or evening bright light exposure does result in melatonin suppression and reduced sleepiness, it is associated with a delay in the natural decline in CBT and higher distal proximal skin temperature gradient (DPG) (see[26] for review). These effects of light are strongly mediated via the intrinsic photosensitive retinal ganglion cells (ipRGC’s), which contain the photopigment melanopsin with a peak sensitivity for wavelengths around 480 nm[27]. It is unknown whether this influence of evening/nighttime light exposure can be reduced by exposure to high light intensities in the preceding daytime or early evening

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