Nutritional status during childhood plays an important role in the human life cycle. The importance of child growth as an indicator for tracking the nutritional and health status of populations is well recognized( Reference de Onis, Blössner and Borghi 1 ). Obesity and thinness are two of the most common nutritional disorders and both are associated with health consequences. Childhood obesity increases the risk of obesity in adulthood and is associated with CVD risk factors such as hypertension, diabetes and dyslipidaemia( Reference Geiss, Parhofer and Schwandt 2 – Reference Herouvi, Karanasios and Karayianni 4 ). Thinness can also result in problems such as osteoporosis, pubertal delay, menstrual irregularity, increased susceptibility to infections, hypothermia, thinning hair and premature mortality( Reference Takimoto, Yoshiike and Kaneda 5 , Reference Misra, Aggarwal and Miller 6 ).
The worldwide prevalence of childhood overweight and obesity has increased dramatically during the past decades, both in developing and developed countries( Reference Lobstein, Baur and Uauy 7 – Reference Karnik and Kanekar 9 ). Recent reports indicate that the increase in childhood obesity is much more rapid in developing countries than in developed countries( Reference de Onis, Blössner and Borghi 10 ). As a populous country, China has now joined the worldwide epidemic of obesity owing to its rapid economic growth and urbanization( Reference Ji and Cheng 11 , Reference Cheng 12 ). In the present paper, based on provincial data in 1985, 1995, 2000, 2005, 2010 and 2014, we report the prevalence trends in different grades of nutritional status (thinness, normal weight, overweight and obesity) among children and adolescents in Shandong, China.
Participants and methods
The study was approved by the Ethical Committee of the Shandong Center for Disease Control and Prevention, Shandong, China.
Study population
Data for the present study were obtained from six national surveys on students’ constitution and health carried out by the government in 1985, 1995, 2000, 2005, 2010 and 2014 in Shandong Province, China. A total of 56 045 students in Shandong Province of Han nationality, aged 7–18 years, were included in the current analysis (14 458 in 1985, 7198 in 1995, 8498 in 2000, 8568 in 2005, 7577 in 2010 and 9746 in 2014). The sample size of age groups in each survey is given in Table 1. The sampling method was stratified multistage sampling based on economic status, drawn from Jinan (the capital and the political, economic and cultural centre of Shandong Province), Yantai (an eastern coastal and developed city) and Jining (a western inland developing city) as survey areas, and using randomly selected primary and secondary schools; the sample proportions in these three areas in each survey were equal. Six public schools (two primary schools, two junior high schools and two senior high schools) from each of the three districts in Shandong were randomly selected and invited to participate in the study. From the selected schools, two classes in each grade were selected and all students of the selected classes were invited to join the study. Most importantly, the schools from which the students were sampled were selected by a leading group in Shandong Province and in general have not allowed change since 1985, and the method and quality control of measurements in the six surveys were the same( 13 ).
Table 1 The sample size in each survey of children and adolescents (n 56 045) aged 7–18 years, Shandong Province, China, 1985–2014
Anthropometric measurements and definitions
All measurements were performed by well-trained health professionals in each of the three districts using the same type of apparatus and following the same procedures( 13 ). Each professional is required to pass a training course for anthropometric measurement organized by the investigation team in Shandong. Height without shoes was measured using metal column height-measuring stands to the nearest 0·1 cm. Weight was measured using lever scales to the nearest 0·1 kg while the students wore light clothes. BMI was calculated from their height and weight (kg/m2). The BMI cut-off points recommended by the International Obesity Task Force were used to define overweight and obesity( Reference Cole, Bellizzi and Flegal 14 ). Thinness was also defined by the international BMI cut-offs( Reference Cole, Flegal and Nicholls 15 ).
Statistical analyses
The prevalence of thinness, overweight and obesity in different survey years was determined. The χ 2 test was used to show significant differences between different years. All analyses were performed with the statistical software package SPSS version 11.5. Significance was defined at the 0·05 level.
Results
The prevalence of thinness, overweight and obesity among children and adolescents aged 7–18 years old in different years is shown in Table 2. A decreasing trend was observed in the prevalence of thinness, from 18·22 % and 23·45 % in 1985 to 7·18 % and 9·49 % in 2014 for boys and girls, respectively (P<0·01). This represents a decrease of 11·04 % in boys and 13·96 % in girls. On the contrary, an increasing trend was observed in the prevalence of overweight and obesity. The prevalence of combined overweight and obesity increased from 1·79 % and 1·66 % in 1985 to 31·12 % and 20·11 % in 2014 for boys and girls, respectively (P<0·01). This represents an increase of 29·32 % in boys and 18·45 % in girls. During the 29-year period, the nutritional profile of children and adolescents had an obvious change (Fig. 1). A decreasing trend was observed in the proportion of normal weight, from 79·98 % and 74·89 % in 1985 to 61·70 % and 70·40 % in 2014 for boys and girls, respectively. This represents a decrease of 18·28 % in boys and 4·49 % in girls.
Fig. 1 Changes in nutritional status (
, normal weight; 
, thinness; 
, overweight and obesity) of children and adolescents (n 56 045) aged 7–18 years, Shandong Province, China, 1985–2014: (a) boys, 1985; (b) boys, 2014; (c) girls, 1985; (d) girls, 2014
Table 2 Prevalence of thinness, overweight and obesity, according to gender, among children and adolescents (n 56 045) aged 7–18 years, Shandong Province, China, 1985–2014
Discussion
During the past decades, China has experienced rapid socio-economic and nutritional transitions, which have led to a more obesogenic environment (e.g. increase in energy intake and decrease in physical activity)( Reference Washington 16 ). The traditional Chinese diet is shifting towards a diet with high fat, high energy density and low dietary fibre( Reference Shang, Li and Liu 17 , Reference Du, Mroz and Zhai 18 ). To the best of our knowledge, the present study is the first examining the shifts in nutritional profile among children and adolescents in Shandong, China, spanning 29 years and using internationally agreed standards. Our results show a rapid increase of overweight and obesity and a decrease of thinness in both boys and girls between 1985 and 2014.
The increasing prevalence of childhood obesity constitutes a serious public health problem in both developed and developing countries. In Shandong Province, the prevalence of obesity was only 0·05 % and 0·04 % for boys and girls, and the prevalence of overweight was less than 2 % in 1985, indicating no obesity epidemic at that time. However, the prevalence rates of obesity plus overweight had reached 31·12 % for boys and 20·11 % for girls in 2014, indicating that childhood overweight and obesity has entered the extensively epidemic stage in this region at present. The reasons include mainly high-energy diet and lifestyle change from being active to sedentary( Reference Karnik and Kanekar 9 ). Comprehensive strategies of intervention should include periodic monitoring and education on nutrition, physical exercise and healthy dietary behaviour( Reference Ji and Cheng 11 ).
The current study examined the shifts in nutritional profile among children and adolescents in Shandong, China spanning 29 years. However, two limitations are noted. First, data for the study were acquired from six independent cross-sectional surveys spanning 29 years rather than from a longitudinal cohort study, thus preventing further assessment of cohort and time effects. Second, the absence of detailed information concerning living environments, dietary patterns and physical activity at the individual level also limited our study.
Acknowledgements
Acknowledgements: The author thanks all of the team members and all participants. Special thanks are extended to Mr B. Yu for providing access to the survey data. Financial support: This study was supported by the Medical and Health Program of Shandong, China (2014WS0376). The surveys on students’ constitution and health were conducted under the auspices of the Department of Education in Shandong Province, China. The funders had no role in the design, analysis or writing of this article. Conflict of interest: None. Authorship: Y.-X.Z. is the sole author. Ethics of human subject participation: The study was approved by the Ethical Committee of the Shandong Center for Disease Control and Prevention, Shandong, China.
