Abstract
Artificial light endows a “round-the-clock”, 24-h/7-d society. Chronic exposure to light at night contributes to health hazards for humans, including disorders of sleep. Yet the influence of inter-individual traits, such as sex-differences, on light sensitivity remains to be established. Here we investigated potential sex-differences to evening light exposure of 40 lx at 6500 K (blue-enriched) or at 2500 K (non-blue-enriched), and their impact on brightness perception, vigilant attention and sleep physiology. In contrast to women, men had higher brightness perception and faster reaction times in a sustained attention task during blue-enriched light than non-blue-enriched. After blue-enriched light exposure, men had significantly higher all-night frontal NREM sleep slow-wave activity (SWA: 2–4 Hz), than women, particularly during the beginning of the sleep episode. Furthermore, brightness perception during blue-enriched light significantly predicted men’s improved sustained attention performance and increased frontal NREM SWA. Our data indicate that, in contrast to women, men show a stronger response to blue-enriched light in the late evening even at very low light levels (40lux), as indexed by increased vigilant attention and sleep EEG hallmarks. Collectively, the data indicate that sex differences in light sensitivity might play a key role for ensuring the success of individually-targeted light interventions.
Highlights
The sharp delineation between day and night existing throughout most of our ancestral evolution has changed in industrialized society
We observed a significant sex difference for light preference, such that men preferred light at 6500 K (62.5%) relative to 2500 K (37.5%), while the opposite was observed for women (6500 K: 12.5%, 2500 K: 87.5%) (Fisher’s Exact Test, p = 0.004) (Fig. 1A)
The seemingly detrimental impact on sleep may be ascribed to the artificial short-wavelength enriched light, which may elicit “carry-over” alerting effects onto the first part of the sleep episode[13,14]
Summary
The sharp delineation between day and night existing throughout most of our ancestral evolution has changed in industrialized society. Exposure to light in the evening/night suppresses the release of the sleep-facilitating hormone melatonin[2,3] It may shift the endogenous circadian clock to a later time[4]. The nighttime impairment in cognitive performance is greater in women than in men[18] It remains to be established if potential sex-differences in cognitive function and sleep regulation may depend on how we respond to light exposure. We investigated whether evening light exposure to a higher (6500 K) and lower (2500 K) proportion of blue spectrum impacts on alertness, brightness perception, performance and sleep EEG activity, and if these effects are susceptible to a putative sex-related vulnerability
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