Participants

A total of 12 426 school students (6750 males and 5676 females) were enrolled in the study, aged 7–17 years from the Longbai community of Minhang District, Shanghai, China. They were selected from one of the thirteen communities in Minhang District by cluster random sampling. Data were collected from 1 November to 31 December in 2017 and were analysed between 15 January and 7 March in 2018. Children and adolescents were eligible for inclusion if they had no disease associated with pathological obesity, or any cardiac, hepatic, kidney, liver or acute/chronic disease. In general, girls begin puberty around 10–11 years and end puberty around 15–17 years, compared with boys at 11–12 and 16–17 years, respectively^(8,9). Therefore, subjects were divided into three age groups (7–10, 11–14 and 15–17 years) which roughly corresponded to pre-pubertal, pubertal and post-pubertal or late-pubertal period.