Relationship between IndiyidualDifference in Melatonin Habitual Bedtime Suppression by Light and Shigekazu Higuchi ] L YIitaka Motohashii

The purposc of this study was to determine rhe relationship bctwcen indiyidual difference in me]atonin suppression by cxposure to Light and habitual bedtimc. Seventeen hca]thy male students (mean age: 22,6± 2,4yr) volunteered to participate in the study, The sub.iects were exposcd to light (1OOO lx) for 2 hours from 2 hours befbre the time of pcak salivary meLatonin concentratien. 'two hours aftcr exposurc 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 sub.jects in whom me]atonin suppression oceurred. Howover, the habitual bcdtime of thc two subjects in w'hom meLatonin suppression did not eccur was earlier than that of the other subjects. Thcse resu]ts suggest that there are some people with very ]ow scnsitivity to light and that this may affect habitual bcdtimc. J Ph.vsivt Anthropol Anpr Hztnian Sci 24(4)r 419-423, 200)http:/,iwww.jstage.jst.go,jp/browse・'jpa [DOI: 10.21 14"jpa.24.4191 Keyvvords: melatonjn suppression, light, sensitivity, bedtime. sleep habits, physiological po]ymorphism