Funding for this research was provided by:
Ministry of Science and Technology of the People's Republic of China (2008BAI58B05)
Received: 24 May 2019
Revised: 11 March 2020
Accepted: 12 March 2020
First Online: 30 March 2020
Compliance with ethical standards
: The authors declare that they have no conflict of interest.
: The study protocol was approved by the Ethical Review Committee of the National Institute for Nutrition and Food Safety, Chinese Centre for Disease Control and Prevention.
: Written informed consent was obtained from parents, the next of kin, carers, or guardians of all the participants.