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

Time schedule. The subjects were exposed to different light conditions (<10, 100, 300, 900 and 2700 lx) from 09:00 to 12:00 and to bright light (300 lx) from 01:00 to 02:30
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Fig1: Time schedule. The subjects were exposed to different light conditions (<10, 100, 300, 900 and 2700 lx) from 09:00 to 12:00 and to bright light (300 lx) from 01:00 to 02:30

Mentions: The experiments were carried out from August 2012 to November 2012; the experimental schedule is shown in Fig. 1. The subjects arrived at the experimental chamber before 23:00 and were exposed to dim light conditions (<10 lx). They slept in the experimental chamber under dark conditions until 08:00 and then had breakfast until 09:00 under the same dim conditions experienced prior to sleep. After breakfast, the subjects experienced light conditions from 09:00 to 12:00. After this exposure, the subjects had lunch until 13:00 under dim light conditions, which were maintained until 01:00, and provided saliva samples every hour from 15:00 to 18:00 in order to determine the threshold of dim light melatonin onset (DLMO) [15, 16]. The subjects were allowed to watch movies and read books in the experimental chamber; however, the illuminance of the movie displays was kept at less than 2 lx, because bright light from movie displays may suppress melatonin secretion [17]. Then, the subjects had dinner and showered from 18:00 to 20:00. Saliva samples were collected under dim light conditions every 30 min from 20:00 to 01:00, and the subjects experienced bright light (300 lx) exposure for 90 min from 01:00 to 02:30. After exposure to bright light, the subjects provided saliva samples. They were instructed to maintain a sitting position on their chairs during saliva collection because posture might affect melatonin secretion [18].Fig. 1


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)

Time schedule. The subjects were exposed to different light conditions (<10, 100, 300, 900 and 2700 lx) from 09:00 to 12:00 and to bright light (300 lx) from 01:00 to 02:30
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig1: Time schedule. The subjects were exposed to different light conditions (<10, 100, 300, 900 and 2700 lx) from 09:00 to 12:00 and to bright light (300 lx) from 01:00 to 02:30
Mentions: The experiments were carried out from August 2012 to November 2012; the experimental schedule is shown in Fig. 1. The subjects arrived at the experimental chamber before 23:00 and were exposed to dim light conditions (<10 lx). They slept in the experimental chamber under dark conditions until 08:00 and then had breakfast until 09:00 under the same dim conditions experienced prior to sleep. After breakfast, the subjects experienced light conditions from 09:00 to 12:00. After this exposure, the subjects had lunch until 13:00 under dim light conditions, which were maintained until 01:00, and provided saliva samples every hour from 15:00 to 18:00 in order to determine the threshold of dim light melatonin onset (DLMO) [15, 16]. The subjects were allowed to watch movies and read books in the experimental chamber; however, the illuminance of the movie displays was kept at less than 2 lx, because bright light from movie displays may suppress melatonin secretion [17]. Then, the subjects had dinner and showered from 18:00 to 20:00. Saliva samples were collected under dim light conditions every 30 min from 20:00 to 01:00, and the subjects experienced bright light (300 lx) exposure for 90 min from 01:00 to 02:30. After exposure to bright light, the subjects provided saliva samples. They were instructed to maintain a sitting position on their chairs during saliva collection because posture might affect melatonin secretion [18].Fig. 1

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