Night eating in Hong Kong adolescents : prevalence and associations with dinner habits, bedtime and weight status

Abstract

Background: With adolescent obesity increasing in many developed and developing countries, many studies have investigated the effects of dietary habits on adolescent obesity. However, night-eating, which may lead to extra caloric intake and weight gain, is understudied. Given adolescents’ behavior patterns required during this period to be likely to influence long term behaviors, the present study investigated the prevalence of night-eating in Hong Kong adolescents and its association with weight status, dinner habits, bedtime, and the interval between dinner time and bedtime.

Methods: This study was a secondary analysis with a sample of 24885 adolescents based on the dataset of Hong Kong Student Surveillance (HKSOS) project which was a school-based cross-sectional survey conducted in 2006/07. The subjects reported the number of days they had night-eating per week, the usual time they had dinner, the time spent on dinner, and bedtime. The interval between dinner time and bedtime was calculated and classified as long (4 hours or more) or short (below 4 hours). Weight status was estimated based on the self-reported weight and height. The prevalence of night-eating and distributions of dinner habits and bedtime were examined using descriptive statistics (mean, standard deviation and percentage). Logistic regression and multiple linear regression models with robust standard errors accounting for school clustering effects were used (Stata 11.0) to estimate crude and adjusted odds ratios (OR) and regression coefficients for associations about night-eating.

Results: Half (50.2%) the subjects reported any night-eating and 21.9% reported frequent night-eating of more than three days a week. The change of BMI z-score was positive associated with night-eating (Coefficient: 0.204; 95%CI: 0.175-0.233), and night-eaters were 13% (95%CI: 6%-20%) more likely to be obese. Compared with early dinner time group, the normal dinner time group was 11% (95% CI: 6%-15%) less likely to have night-eating. Students who reported normal and slow eating speed were 30% (95 % CI: 22%-39%) and 147% (95% CI: 113%-187%) more likely to have night-eating compared with quick eating speed group; the late-sleepers were 43% (95% CI: 35%--53%) and 25% (95%CI: 18%--34%) more likely to have night-eating on weekday and weekend, respectively, compared with early-sleepers. Besides, it was observed that adolescents having longer interval between dinner time and bedtime were 22% (95% CI: 5%--42%) more likely to have night-eating.

Conclusion: The prevalence of night-eating was 50.2% in Hong Kong students. The night-eating was positively related with obesity, and the relationship was the first time to be estimated in Hong Kong adolescents. Besides, the relative early dinner time (compared with bedtime), slow dinner speed, late bedtime and long interval between dinner time and bedtime were positively associated with night-eating.