Journal of PHYSIOLOGICAL ANTHROPOLOGY and Applied Human Science
Online ISSN : 1347-5355
Print ISSN : 1345-3475
Relationship between Individual Difference in Melatonin Suppression by Light and Habitual Bedtime
Shigekazu HiguchiYutaka MotohashiTakafumi MaedaKeita Ishibashi
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2005 Volume 24 Issue 4 Pages 419-423


The purpose of this study was to determine the relationship between individual difference in melatonin suppression by exposure to light and habitual bedtime. Seventeen healthy male students (mean age: 22.6±2.4 yr) volunteered to participate in the study. The subjects were exposed to light (1000 lx) for 2 hours from 2 hours before the time of peak salivary melatonin concentration. Two hours after exposure to the light, melatonin suppression had occurred in fifteen subjects. No significant correlation was found between the rate of melatonin suppression and habitual bedtime in the fifteen subjects in whom melatonin suppression occurred. However, the habitual bedtime of the two subjects in whom melatonin suppression did not occur was earlier than that of the other subjects. These results suggest that there are some people with very low sensitivity to light and that this may affect habitual bedtime.

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© 2005 Japan Society of Physiological Anthropology
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