Temporal changes in obesity and sleep habits in Hong Kong Chinese school children: a prospective study

We examined the temporal changes in obesity and sleep habits and their relationship in a prospective cohort of healthy Chinese adolescents. We collected data on anthropometric and questionnaire-measured sleep parameters in 2007–2008. 516 participants returned for examinations in 2013–2015. General obesity was defined as body mass index (BMI) ≥age- and sex-specific 95(th) percentile or ≥25 kg/m(2) for participants aged <18 or ≥18 years, respectively. Central obesity was defined as waist circumference (WC) ≥ age- and sex-specific 90(th) percentile or using adult cut-offs. After a mean follow-up of 6.2 ± 0.5 years, the mean BMI increased from 18.5 ± 3.1 to 20.9 ± 3.4 kg/m(2). The corresponding WC were 63.7 ± 8.9 and 69.8 ± 9.7 cm. General obesity rate increased from 8.3% (95% confidence interval [CI] 6.1–11.1) to 11.3% (8.7–14.4; p = 0.034). Central obesity rate decreased from 16.9% (13.7–20.4) to 13.5% (10.6–16.8; p = 0.034). During follow-up, more participants reported short sleep (<7 hours/day during weekday: 20.5% [17.1–24.2] vs. 15.3% [12.3–18.8]; p = 0.033) and bedtime after midnight (60.5% [56.2–64.8] vs. 16.2% [13.1–19.7]; p < 0.001) than baseline. The relative risk of overweight/obesity in participants with short sleep and late bedtime was 1.30 (0.48–3.47) and 1.46 (0.70–3.05), respectively. Despite rising rates of unhealthy sleep habits and general obesity, their associations were not significant at 6-year of follow-up.