Background:
The secular trend and longitudial relationship between obesity and sleep in adolescents are under-explored. We aimed to examine the secular trend and longitudinal association between obesity and sleep habits in Hong Kong Chinese school children.
Methods:
Based on a cohort of Hong Kong Chinese school children surveyed in 2007-2008, who were all healthy volunteers with well-documented anthropometric parameters and sleep patterns using validated questionnaires, we called back 516 participants to have follow-up examinations in 2013-2015. Obesity was defined as body mass index (BMI) ≥95th percentile for aged <18 years or ≥25 kg/m2 for those aged ≥18 years. Central obesity was defined as 90th percentile of waist circumference (WC) or adult cut-off if lower.
Results:
Mean age of this prospective cohort was 12.8 years (standard deviation, SD 3.6) at baseline and 19.0 years (SD 3.6) at follow-up. 37.6% were male. BMI at baseline and follow-up were 18.5 (SD 3.1) and 20.9 (SD 3.4) kg/m2. The respective figures for WC were 63.7 (SD 8.9) and 69.8 (SD 9.7) cm. The rate of obesity was 8.3% (95% confidence interval CI=6.1-11.1) at baseline and 11.3% (CI=8.7-14.4), p=0.034. By contrast, there was a significant decline in the frequency of central obesity [16.9% (CI=13.7-20.4) vs 13.5% (CI=10.6-16.8%), p=0.034]. Compared to sleep habits at baseline, more participants reported short sleep duration (<7 hours per day during weekday) [15.3% (CI=12.3-18.8) vs 20.5% (CI=17.1-24.2), p=0.033] and bedtime after midnight [16.2% (CI=13.1-19.7) vs 60.5% (CI=56.2-64.8), p<0.001] during follow-up.
Conclusion:
There was an increasing rate of general obesity but a decreasing trend of central obesity in our youth population. There were significantly more participants reported short sleep duration and late bedtime during follow-up. No significant association between obesity and sleep habits were found. Long-term study would be required to address the health consequences of unhealthy sleeping habits.