Melatonin suppression does not automatically alter sleepiness, vigilance, sensory processing, or sleep

Abstract

Pre-sleep exposure to short-wavelength light suppresses melatonin and decreases sleepiness with activating effects extending to sleep. This has mainly been attributed to melanopic effects, but mechanistic insights are missing. Thus, we investigated whether two light conditions only differing in the melanopic effects (123 vs. 59 lux melanopic EDI) differentially affect sleep besides melatonin. Additionally, we studied whether the light differentially modulates sensory processing during wakefulness and sleep. Twenty-nine healthy volunteers (18-30 years, 15 women) were exposed to two metameric light conditions (high- vs. low-melanopic, ≈60 photopic lux) for 1 hour ending 50 min prior to habitual bed time. This was followed by an 8-h sleep opportunity with polysomnography. Objective sleep measurements were complemented by self-report. Salivary melatonin, subjective sleepiness, and behavioural vigilance were sampled at regular intervals. Sensory processing was evaluated during light exposure and sleep on the basis of neural responses related to violations of expectations in an oddball paradigm. We observed suppression of melatonin by ≈14 % in the high- compared to the low-melanopic condition. However, conditions did not differentially affect sleep, sleep quality, sleepiness, or vigilance. A neural mismatch response was evident during all sleep stages, but not differentially modulated by light. Suppression of melatonin by light targeting the melanopic system does not automatically translate to acutely altered levels of vigilance or sleepiness or to changes in sleep, sleep quality, or basic sensory processing. Given contradicting earlier findings and the retinal anatomy, this may suggest that an interaction between melanopsin and cone-rod signals needs to be considered.

Managing Circadian Disruption due to Hospitalization: A Pilot Randomized Controlled Trial of the CircadianCare Inpatient Management System

“…The lack of significant differences in sleep timing and sleep quality indices (sleep diaries or actigraphy) between patients grouped by DLMO onset, DLMO offset, and non-calculable DLMO, at T0 or T1, may be in relation to the complexity of the condition of the patients, the limited number of DLMO available, and the fact that the timing of melatonin production is obviously not the sole determinant of sleep timing/ quality (Lavie, 1997;De Rui et al, 2015;Blume et al, 2022), especially in a complex and unusual situation such as hospitalization. The lack of a relationship between melatonin profiles and subjective or objective sleep-wake variables may also suggest that confounders such as medication or illness per se may play a relevant role on melatonin profile shape and DLMO/DLMOff computability/timing in clinical populations.…”

ICNIRP Statement on Short Wavelength Light Exposure from Indoor Artificial Sources and Human Health

“…While one study reported increased sleepiness the other study found no effect (Xu 2018). Interestingly, a recent study by the Cajochen group (Blume et al 2022) found that although melatonin was suppressed by nighttime exposure to SWL, this did not translate to altered levels of vigilance or sleepiness. The authors suggest that an interaction between melanopsin and cone-rod signals needs to be considered.…”

Light as a Modulator of Non-Image-Forming Brain Functions—Positive and Negative Impacts of Increasing Light Availability

“…Light exposure can also have acute NIF impacts on alertness, sleep, and cognition, all with a sensitivity shifted toward shorter wavelength light (~460 nm) [ 5 , 67 , 68 , 69 , 70 , 71 ]. Though, it should be noted that the acute NIF effects of light may not be due to a direct result of melatonin suppression through melanopsin-ipRGC suppression [ 72 ]. Light impact on alertness has been measured with subjective and objective measures with both kinds showing that light exposure increases alertness.…”