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. 2023 Oct 23;5(4):615-626.
doi: 10.3390/clockssleep5040041.

Relationship between Circadian Phase Delay without Morning Light and Phase Advance by Bright Light Exposure the Following Morning

Michihiro Ohashi  1   2 , Taisuke Eto  2   3   4 , Toaki Takasu  1 , Yuki Motomura  3 , Shigekazu Higuchi  3
Affiliations

Relationship between Circadian Phase Delay without Morning Light and Phase Advance by Bright Light Exposure the Following Morning

Michihiro Ohashi et al. Clocks Sleep. .

Abstract

Humans have a circadian rhythm for which the period varies among individuals. In the present study, we investigated the amount of natural phase delay of circadian rhythms after spending a day under dim light (Day 1 to Day 2) and the amount of phase advance due to light exposure (8000 lx, 4100 K) the following morning (Day 2 to Day 3). The relationships of the phase shifts with the circadian phase, chronotype and sleep habits were also investigated. Dim light melatonin onset (DLMO) was investigated as a circadian phase marker on each day. In the 27 individuals used for the analysis, DLMO was delayed significantly (-0.24 ± 0.33 h, p < 0.01) from Day 1 to Day 2 and DLMO was advanced significantly (0.18 ± 0.36 h, p < 0.05) from Day 2 to Day 3. There was a significant correlation between phase shifts, with subjects who had a greater phase delay in the dim environment having a greater phase advance by light exposure (r = -0.43, p < 0.05). However, no significant correlations with circadian phase, chronotype or sleep habits were found. These phase shifts may reflect the stability of the phase, but do not account for an individual's chronotype-related indicators.

Keywords: circadian phase; dim light melatonin onset; light; photoentrainment; sleep.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Individual data of absolute DLMO for (a) Day 1 to Day 2 (PS1, (b)) and Day 2 to Day 3 (PS2, (c)). Black-framed squares indicate DLMO averages for each day (NS: not significant, *: p < 0.05, **: p < 0.01).
Figure 2
Figure 2
Correlation between PS1 and PS2. The points indicate individual data and the black line indicates the regression line.
Figure 3
Figure 3
Correlation between circadian time of light exposure (start time) and PS2. The points indicate individual data and the black line indicates the regression line.
Figure 4
Figure 4
Example of the experimental protocol setup to take into account the predicted DLMO with reference to MSFsc. This figure shows an example in the case of predicted DLMO = 23:00. This schedule was shifted in 30 min increments according to the individual’s predicted DLMO.
See this image and copyright information in PMC

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