Funding for this research was provided by:
Guangzhou Medical Foundation (20131A031001)
Text and Data Mining valid from 2019-02-20
Received: 26 June 2018
Accepted: 7 February 2019
First Online: 20 February 2019
Ethics approval and consent to participate
: Permission to conduct the study was granted by the Guangzhou Departments of Education and Health. The study was approved by the Ethical Committee of Guangzhou Centre for Disease Control and Prevention. Informed consent for the measurements was obtained from the parents of all eligible children, and verbal consent was obtained from the children at the time of measurement.
: Not applicable.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.