Limits...
Effects of day-time exposure to different light intensities on light-induced melatonin suppression at night.

Kozaki T, Kubokawa A, Taketomi R, Hatae K - J Physiol Anthropol (2015)

Bottom Line: However, bright light exposure during the day-time might reduce light-induced melatonin suppression (LIMS) at night.This study aims to evaluate the effect of different day-time light intensities on LIMS.These findings may be useful in implementing artificial light environments for humans in, for example, hospitals and underground shopping malls.

View Article: PubMed Central - PubMed

Affiliation: Faulty of Design, Kyushu University, 4-9-1 Shiobaru, Fukuoka city, Minami-ku, Japan. kozaki@design.kyushu-u.ac.jp.

ABSTRACT

Background: Bright nocturnal light has been known to suppress melatonin secretion. However, bright light exposure during the day-time might reduce light-induced melatonin suppression (LIMS) at night. The effective proportion of day-time light to night-time light is unclear; however, only a few studies on accurately controlling both day- and night-time conditions have been conducted. This study aims to evaluate the effect of different day-time light intensities on LIMS.

Methods: Twelve male subjects between the ages of 19 and 23 years (mean ± S.D., 20.8 ± 1.1) gave informed consent to participate in this study. They were exposed to various light conditions (<10, 100, 300, 900 and 2700 lx) between the hours of 09:00 and 12:00 (day-time light conditions). They were then exposed to bright light (300 lx) again between 01:00 and 02:30 (night-time light exposure). They provided saliva samples before (00:55) and after night-time light exposure (02:30).

Results: A one-tailed paired t test yielded significant decrements of melatonin concentration after night-time light exposure under day-time dim, 100- and 300-lx light conditions. No significant differences exist in melatonin concentration between pre- and post-night-time light exposure under day-time 900- and 2700-lx light conditions.

Conclusions: Present findings suggest the amount of light exposure needed to prevent LIMS caused by ordinary nocturnal light in individuals who have a general life rhythm (sleep/wake schedule). These findings may be useful in implementing artificial light environments for humans in, for example, hospitals and underground shopping malls.

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Related in: MedlinePlus

Mean (+S.D.) melatonin concentrations of each morning light condition before (pre-exposure) and after (post-exposure) the nocturnal light exposure
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Fig4: Mean (+S.D.) melatonin concentrations of each morning light condition before (pre-exposure) and after (post-exposure) the nocturnal light exposure

Mentions: The time courses for mean melatonin concentrations under the five different light conditions are shown in Fig. 3. There were no significant differences in the DLMO phase for each light condition (F1.36 = 1.4, n.s., β = 0; Table 1). Figure 4 shows mean melatonin concentrations of each morning light condition before (pre-exposure) and after (post-exposure) the nocturnal light exposure. Two-way, repeated-measured ANOVA for the experiment period demonstrated that time intervals have a significant effect on melatonin secretion (F1.9 = 15.8, p < 0.01, β = 0) and interact with light conditions (F4.36 = 5.4, p < 0.01, β = 0), and light conditions do not have a significant effect (F4.36 = 0.10, n.s., β = 0.37). Post hoc comparison revealed significant melatonin decrements after night-time light exposures under day-time dim, 100 and 300 lx light conditions (dim; t9 = 8.7, p < 0.01, β = 0: 100 lx; t9 = 1.9, p < 0.05, β = 0.47: 300 lx; t9 = 1.9, p < 0.05, β = 0.46). No significant differences were present in the melatonin concentrations between night-time pre- and post-light exposure of day-time 900 and 2700 lx light conditions (900 lx; t9 = 1.1, n.s., β = 0.73; 2700 lx; t9 = 0.4, n.s., β = 0.90).Fig. 3


Effects of day-time exposure to different light intensities on light-induced melatonin suppression at night.

Kozaki T, Kubokawa A, Taketomi R, Hatae K - J Physiol Anthropol (2015)

Mean (+S.D.) melatonin concentrations of each morning light condition before (pre-exposure) and after (post-exposure) the nocturnal light exposure
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4491270&req=5

Fig4: Mean (+S.D.) melatonin concentrations of each morning light condition before (pre-exposure) and after (post-exposure) the nocturnal light exposure
Mentions: The time courses for mean melatonin concentrations under the five different light conditions are shown in Fig. 3. There were no significant differences in the DLMO phase for each light condition (F1.36 = 1.4, n.s., β = 0; Table 1). Figure 4 shows mean melatonin concentrations of each morning light condition before (pre-exposure) and after (post-exposure) the nocturnal light exposure. Two-way, repeated-measured ANOVA for the experiment period demonstrated that time intervals have a significant effect on melatonin secretion (F1.9 = 15.8, p < 0.01, β = 0) and interact with light conditions (F4.36 = 5.4, p < 0.01, β = 0), and light conditions do not have a significant effect (F4.36 = 0.10, n.s., β = 0.37). Post hoc comparison revealed significant melatonin decrements after night-time light exposures under day-time dim, 100 and 300 lx light conditions (dim; t9 = 8.7, p < 0.01, β = 0: 100 lx; t9 = 1.9, p < 0.05, β = 0.47: 300 lx; t9 = 1.9, p < 0.05, β = 0.46). No significant differences were present in the melatonin concentrations between night-time pre- and post-light exposure of day-time 900 and 2700 lx light conditions (900 lx; t9 = 1.1, n.s., β = 0.73; 2700 lx; t9 = 0.4, n.s., β = 0.90).Fig. 3

Bottom Line: However, bright light exposure during the day-time might reduce light-induced melatonin suppression (LIMS) at night.This study aims to evaluate the effect of different day-time light intensities on LIMS.These findings may be useful in implementing artificial light environments for humans in, for example, hospitals and underground shopping malls.

View Article: PubMed Central - PubMed

Affiliation: Faulty of Design, Kyushu University, 4-9-1 Shiobaru, Fukuoka city, Minami-ku, Japan. kozaki@design.kyushu-u.ac.jp.

ABSTRACT

Background: Bright nocturnal light has been known to suppress melatonin secretion. However, bright light exposure during the day-time might reduce light-induced melatonin suppression (LIMS) at night. The effective proportion of day-time light to night-time light is unclear; however, only a few studies on accurately controlling both day- and night-time conditions have been conducted. This study aims to evaluate the effect of different day-time light intensities on LIMS.

Methods: Twelve male subjects between the ages of 19 and 23 years (mean ± S.D., 20.8 ± 1.1) gave informed consent to participate in this study. They were exposed to various light conditions (<10, 100, 300, 900 and 2700 lx) between the hours of 09:00 and 12:00 (day-time light conditions). They were then exposed to bright light (300 lx) again between 01:00 and 02:30 (night-time light exposure). They provided saliva samples before (00:55) and after night-time light exposure (02:30).

Results: A one-tailed paired t test yielded significant decrements of melatonin concentration after night-time light exposure under day-time dim, 100- and 300-lx light conditions. No significant differences exist in melatonin concentration between pre- and post-night-time light exposure under day-time 900- and 2700-lx light conditions.

Conclusions: Present findings suggest the amount of light exposure needed to prevent LIMS caused by ordinary nocturnal light in individuals who have a general life rhythm (sleep/wake schedule). These findings may be useful in implementing artificial light environments for humans in, for example, hospitals and underground shopping malls.

Show MeSH
Related in: MedlinePlus