Trends and inequalities in thinness and obesity among Chinese children and adolescents: evidence from seven national school surveys between 1985 and 2019

Background: There are little recent data in China regarding contemporary nutritional inequities among children and adolescents, particularly in relation to urban-rural residence and regional socioeconomic status (SES). We aim to assess inequalities in thinness and obesity in Chinese children and adolescents. Methods: Weight and height measurements for 1 677 261 children and adolescents aged 7-18 years were obtained from seven cycles of the Chinese National Surveys on Students Constitution and Health (1985, 1995, 2000, 2005, 2010, 2014, and 2019). Sex-specific BMI-for-age Z scores were applied to define thinness (Z scores <-2SD) and obesity (Z scores >+2SD). Urban-rural classification came from the Statistical Urban and Rural Division Code, and gross domestic product (GDP) per capita in the province in which the school was situated was used as a proxy for SES. T1 represented the provinces with the most disadvantaged SES and T3 represented the provinces with the most advantaged SES. General linear regression models assessed correlations between prevalence and GDP per capita, with projections to 2030 derived from best-fitting models. Findings: The mean prevalence of obesity rose from 0<middle dot>10% (95% CI 0<middle dot>09 to 0<middle dot>11) in 1985 to 8<middle dot>25% (8<middle dot>13 to 8<middle dot>37) in 2019, whereas thinness prevalence decreased from 8<middle dot>49% (8<middle dot>41 to 8<middle dot>58) to 3<middle dot>37% (3<middle dot>29 to 3<middle dot>45). High SES provinces exhibited a significant drop in obesity prevalence from 2014 (8<middle dot>42% [8<middle dot>19 to 8<middle dot>65]) to 2019 (7<middle dot>73% [7<middle dot>52 to 7<middle dot>95]). Nationally, the prevalence of obesity was consistently higher in urban areas than in rural areas for both sexes from 1985 to 2019; however, a greater prevalence of obesity was observed in rural than urban girls residing in T3 regions in 2019 (urban-rural gap: -0<middle dot>37% [-0<middle dot>07 to -0<middle dot>80]). Rural boys had a higher prevalence of thinness than their urban counterparts across all survey waves, with the exceptions of 1985 and 1995. For girls, no significant urban-rural gap in thinness was observed in the most recent survey in 2019 (-0<middle dot>10% [-0<middle dot>24 to 0<middle dot>04]). From 1985 to 2014, boys and girls from high SES regions had a higher risk of obesity and a lower risk of thinness than those from low SES regions. However, in 2019, a nationwide shift occurred, and the T3-T1 difference in obesity approached or went below zero for boys (-0<middle dot>49% [-1<middle dot>02 to 0<middle dot>04]) and girls (-0<middle dot>68% [-1<middle dot>00 to -0<middle dot>35]). T3-T1 differences in thinness also approached zero for boys (-0<middle dot>46% [-0<middle dot>77 to -0<middle dot>14]) and girls (-0<middle dot>14% [-0<middle dot>43 to 0<middle dot>15]). The projected estimates to 2030 for urban-rural obesity gaps (boys: -1<middle dot>00% [-2<middle dot>65 to 0<middle dot>65]; girls: -2<middle dot>88% [-6<middle dot>91 to 1<middle dot>15]) and T3-T1 obesity differences (boys: -8<middle dot>88% [-13<middle dot>76 to -4<middle dot>01]; girls: -8<middle dot>82% [-12<middle dot>78 to -4<middle dot>85]) were both negative, with forecasted estimates for urban-rural gaps and T3-T1 differences in thinness prevalence in 2030 close to zero for both boys and girls. Interpretation: China's socioeconomic development continues to influence within-country inequities regarding the regional distribution of child and adolescent weight according to urban-rural location and regional SES. Contemporary Chinese children and adolescents in socioeconomically disadvantaged regions and rural areas constitute a vulnerable population facing nutritional risk, but from obesity rather than thinness. Disrupting projected inequities in obesity will require extensive preventive investments.