Funding for this research was provided by:
Russian Foundation for Basic Research (18-013-01026)
Received: 16 September 2019
Accepted: 15 October 2019
First Online: 11 November 2019
Compliance with ethical standards
: The present study was performed in agreement with the ethical standards set in the Declaration of Helsinki (1964) and its later amendments. The protocol of the investigation was approved by the Institutional Ethics Committee (Yaroslavl State University, Yaroslavl, Russia). Informed consent was obtained from the parents, who were informed about the study. All procedures involving children (hair sampling, anthropometric analysis) were performed in presence of parents or their legal representatives.
: The authors declare no conflict of interest