PARENTAL ENFORCEMENT OF BEDTIME DURING CHILDHOOD MODULATES PREFERENCE OF JAPANESE JUNIOR HIGH SCHOOL STUDENTS FOR EVENINGNESS CHRONOTYPE

We examined the effect of home bedtime discipline during childhood on morningness and eveningness (M-E) preference by Japanese junior high school students. M-E was assessed by the M-E Questionnaire (MEQ) of Torsvall and ?kerstedt (the higher the score, the greater the preference for morningness), and parental determination of bedtime during childhood was ascertained using an original questionnaire. The average M-E score of adolescents living in urban Kochi City (mean ± SD; 15.10 ± 3.42) was significantly lower (P < .01) than the score of those in suburban districts (16.14 ± 3.44). Overall, 43.1% of the junior high school students in Kochi City compared to 53.0% of the students living in suburban districts had their bedtime decided during childhood by parents (P < .01). In Kochi City, the M-E score for boys (14.62 ± 3.51) was lower (P < .01) than girls (15.53 ± 3.28). During childhood, parents decided the bedtime for 49% of the girls compared to 36.6% of the boys (P < .01). Boys whose bedtime was not decided by parents during childhood had a somewhat stronger preference for eveningness (14.20 ± 3.53) (P < .05) compared to those whose bedtime was decided by parents (15.12 ± 3.36). The results suggest bedtime discipline at home during childhood has an effect on adolescent chronotype, modulating the extent of shift to eveningness in Japanese junior high school boys in particular. (Chronobiology International, 18(5), 823–829, 2001)