Hitomi Kanayama

Morning-evening preference: sleep pattern spectrum and lifestyle habits among Japanese junior high school pupils.

We surveyed the sleep‐wake patterns and lifestyle habits in a sample of Japanese first to third year junior high school children (n=638, age 12 to 15 yrs), of whom 29.3% were evening type, 64.1% intermediate type, and 6.6% morning type in preference. The morningness‐eveningness (M‐E) score was lower (more evening typed), 16.1 vs. 15.4 in first compared to third year students. There were significant gender differences, with girls showing a greater evening preference. Evening preference was associated with longer sleep latency, shortened sleep duration during schooldays and weekends, bad morning feeling, and episodes of daytime sleepiness. In contrast, morning preference was associated with higher sleep drive and better sleep‐wake parameters and lifestyle habits. Our results suggest the morning preference should be promoted among junior high school children to increase the likelihood of more regular sleep‐wake patterns and lifestyle habits.

Body Image, Body Satisfaction and Dieting Behavior in Japanese Preadolescents: The Toyama Birth Cohort Study

ObjectivesTo examine the relationships between body image, body satisfaction and dieting behavior in the context of pubertal changes in Japanese preadolescents.MethodsA cross-sectional study of dieting behavior among 5,244 preadolescents (2,452 boys and 2,792 girls aged 12–13) born in Toyama prefecture.ResultsThe percentages of those who perceived themselves fat, wanted to be thinner, and had tried dieting, which increased with body mass index (BMI), were significantly higher in girls than in boys (34.2% vs. 20.0%, 58.0% vs. 26.0%, and 17.3% vs. 5.7%, respectively). Independent of sex and BMI, those who wanted to be thinner and those who had tried dieting were more frequently observed in those who perceived themselves fat, and those who had tried dieting were more frequently observed in those who wanted to be thinner. Pubertal changes were significantly associated with dieting behavior, but their relationships to body image and body satisfaction differed between sexes; for boys, those who perceived themselves fat were more frequently observed in those without pubertal changes; whereas for girls, those who wanted to be thinner were more frequently observed in those with pubertal changes.ConclusionsDieting behavior of Japanese preadolescents was associated with whether they perceived themselves fat and wanted to be thinner, sometimes independent of whether they were actually overweight. Pubertal changes might induce a positive perspective of growing fat among boys and a desire to be thinner among girls, with the consequence that dieting behavior would be reinforced in those with pubertal changes.

Body Image and Body Satisfaction Play Important Roles in the Path to Dieting Behavior in Japanese Preadolescents: The Toyama Birth Cohort Study

ObjectivesTo analyze the path to dieting behavior in Japanese preadolescents.MethodsA cross-sectional study of dieting behavior among 5,244 preadolescents (2,452 boys and 2,792 girls aged 12–13) born in Toyama prefecture.ResultsWhile increasing with body mass index (BMI), the percentage of those who had tried dieting was higher in those who perceived themselves fat than in those who perceived themselves thin or average. Of those who wanted to be thinner, 16.1% of boys and 26.8% of girls had tried dieting. Path analysis in nonobese subjects (2,116 boys and 2,334 girls) showed that (1) body image was primarily based on BMI, (2) body image led to body dissatisfaction, and (3) body dissatisfaction led to dieting behavior. Pubertal changes had a significant effect on body image (path coefficient <0)for boys and body satisfaction (path coefficient >0) for girls, in addition to that on BMI. Maternal BMI had a significant effect on BMI but not on body image, body satisfaction, or dieting behavior.ConclusionsBody image and body satisfaction play important roles in the path to dieting behavior in Japanese preadolescents. Pubertal changes may reinforce dieting behavior, but the mechanism may differ by sex.