Secular trends and urban-rural disparities in the median age at menarche among Chinese han girls from 1985 to 2019

Age at menarche and depression: an updated systematic review and meta-analysis

BACKGROUND

Age at menarche may influence the onset of depression later in life. We aim to assess the association between early/late menarche and depressive outcomes in females by updating a systematic review and meta-analysis.

METHODS

The search of the original systematic review was updated for studies published in PubMed, Embase, and Cochrane Library from 2013 to 2023. The early/late and on-time menarche divisions were generally based on each study. Depression or depressive symptoms could be measured through various validated tools and diagnostic criteria. We assessed the quality of the evidence using the GRADE approach and performed a random-effect meta-analysis with age at menarche and the cases of depression as outcomes.

RESULTS

We included eight cohort and three cross-sectional studies (138,819 participants). Females with early menarche were more likely to have depression later in life compared with those who had on-time menarche (early vs. on-time menarche: odds ratio (OR) = 1.11; 95% confidence interval (CI): 1.03, 1.20; I2 = 44.5%). We found a null association between late menarche and depression for females (late vs. on-time menarche: odds ratio (OR) = 1.00; 95% confidence interval (CI): 0.87, 1.15; I2 = 73.2%). Sensitivity analyses showed that the results were robust. The quality of the available evidence was rated as very low.

CONCLUSIONS

Existing evidence suggests that early menarche may be associated with an increased risk of depression in females. But it remains unclear about late menarche. More high-quality studies are warranted.

Height development trends among 7-18-year-old school-age children in central plains of China between 2000 and 2019: A serial cross-sectional surveillance study in China

OBJECTIVE

The aim of this study was to analyze changes in height of 7-18-year-old school-age children in China during the year of 2000-2019.

METHODS

We used the survey data from the Chinese National Survey on Students' Constitution and Health in Henan Province for the years 2000, 2005, 2010, 2014, and 2019. Data were categorized into subgroups based on geographic location, gender, and age; mean, standard deviation, and Pearson's correlation coefficient were used to analyze trends in height change among children and adolescents and the correlation between socioeconomic indicators and height change.

RESULTS

The height of children and adolescents in Henan has shown a continuous upward trend. The height difference between urban and rural areas has gradually narrowed but has not disappeared. The correlation of height development trends between neighbouring urban areas was higher than in other areas. The level of medical care was significantly associated with the change in height for both boys (r = 0.950, p = 0.013) and girls (r = 0.897, p = 0.039); GDP per capita (r = 0.940，p = 0.018) was significantly associated with the change in height for boys only.

CONCLUSION

The height of Chinese children and adolescents will continue to maintain a positive growth trend, but we need to pay attention to the health status and nutritional intake of children and adolescents in economically disadvantaged areas in order to narrow the height disparity between different socio-economic groups.

Secular Trends in the Median Age at Menarche and Spermarche Among Chinese Children From 2000 to 2019 and Analysis of Physical Examination Indicators Factor

OBJECTIVES

This research aimed to understand the long-term trends in the age of menarche among girls and spermarche among boys, and to analyze the factors that may influence the onset of menarche and first spermarche.

METHODS

The study was based on data from 49 566 students in Henan Province collected from the Chinese National Surveys on Students' Constitution and Health (CNSSCH) conducted between 2000 and 2019. Median age at menarche and spermarche was estimated by probit analysis. t-Tests were used to analyze the influence of menarche and first spermarche on physical examination indexes of adolescent children, and the chi-squared test was used to compare whether the differences in physical activity were statistically significant.

RESULTS

The age at menarche has decreased from 12.33 years in 2000 to 12.00 years in 2019, and the age at first spermarche has decreased from 14.01 years in 2000 to 13.99 years in 2019. The age at first spermarche in urban boys (13.61 years in 2000; 12.94 years in 2014) was consistently younger than that in rural boys (14.43 years in 2000; aged 13.08 in 2014), except in 2019. The age of menarche in urban girls (12.23 years in 2000; 11.89 years in 2019) was always earlier than that in rural girls (12.44 years in 2000; 12.05 years in 2019).

CONCLUSIONS

The age at menarche and spermarche for children in Henan Province generally showed a decreasing trend from 2000 to 2019. The status of BMI is significantly associated with the early onset of puberty in children.

Socioeconomic Status and Age at Menarche in Türkiye

OBJECTIVES

The trend in declining age at menarche (AAM) largely continues while body size increases globally. The aim was to investigate trends in AAM, menstrual characteristics, and post-menarcheal anthropometric parameters in adolescents living in an urban area in Türkiye between 1999 and 2018.

METHODS

Female adolescent high school students in the Manisa region were asked about menarche and socioeconomic status (SES). There were 1017 girls in the first study (1999-2001) and 1304 (2016-2018) in the second study. Height and weight were measured. Body mass index (BMI) was calculated. Adolescent girls were grouped into three socioeconomic status (SES) groups based on parental education and occupation, and all parameters were evaluated using SES.

RESULTS

The mean ± standard deviation for AAM in the first period was 12.82 ± 1.07 years and 12.83 ± 0.9 years in the second. AAM did not differ between the two periods nor between SES groups in either period. Post-menarcheal height, weight, and BMI increased in the second period compared to the first study and across all SES groups (p < 0.05). The whole group AAM was similar in both periods, only 3 months earlier in the second period than in the first period. However, the AAM in girls with a post-menarcheal BMI indicating being overweight or obese was significantly earlier than that of those with a normal post-menarcheal BMI in both periods (p < 0.05).

CONCLUSIONS

Despite changing sociodemographic characteristics and an increasing trend in height, weight, and BMI in all socioeconomic groups, no change was observed in mean AAM in an urban region of Western Türkiye over 18 years. While the inverse relationship between BMI and postmenarcheal BMI continued in both periods, the decline in AAM became more pronounced over the years in the presence of high postmenarcheal BMI.

Assessment of the differences in Mean Age at Menarche (MAM) among adolescent girls in rural and urban Nigeria: a systematic review

INTRODUCTION

Globally, there has been a decline in the age of menarche; the decline is higher in poorer countries than in richer ones. The measurement of the decline was based on the reported mean age at menarche (MAM) across the countries. There is a significant knowledge gap in investigating the generational decline in MAM in low- and median-income countries (LMC). In Nigeria, different studies have reported MAM, but none have attempted to investigate the generational shift in the reported MAM in girls residing in rural and urban areas. This review sought to understand if there is a rural-urban disparity in the MAM.

METHODS

Documents were searched in the relevant bibliometric database and Population intervention, comparison(s) and outcome (PICO) framework were used as eligibility criteria for extracting data from the documents based on some inclusion and exclusion criteria. The population are adolescent schoolgirls in rural and urban settlements in Nigeria. The comparator is the age of menarche of urban versus rural adolescent schoolgirls in Nigeria, while the mean age at menarche (MAM) is the outcome. Data quality assessment was done to critically appraise the included studies and enhance. Data were synthesized using narrative review, descriptive and inferential statistics.

RESULTS

Ten articles were included in the study, following the PRISMA framework. The overall mean evaluation of the risk of bias in the individual studies included in the review was computed to be 88%. Generally, there seems to be a decline in the age at menarche from 1976 to 2023. The rural MAM is higher than the urban MAM, and the gap between the two appears to be narrowing. The t-test showed no statistically significant mean differences between the rural and urban mean age at menarche (T = 2.1009, p value = 0.4679). The mean menarcheal age for girls in rural and urban areas is 13.44 and 13.04, respectively. There is a strong positive correlation between the rural and urban MAMs (Pearson = 0.93, p < 0.001). The Gaussian kernel estimated a bimodal distribution for rural girls, where they are most likely to experience menarche at 11 and 13 years, respectively, while urban girls are most likely to experience menarche at 13 years. In both locations, the incidence of menarche decreases just after the peak at 13 years.

CONCLUSION

Although rural girls have delayed menarche, there is no statistically significant mean difference between the age at menarche reported for rural and urban areas in Nigeria. Interventions in the form of counseling and reproductive education are recommended. The review provides a strong foundation for further research and policy development aimed at improving the health and well-being of adolescent girls in Nigeria and other similar settings.

PROSPERO REGISTRATION

CRD42024529497.

Trend in physical growth among Chinese urban students: Results from five national successive cross-sectional surveys within the past two decades

OBJECTIVES

To examine the orientation, magnitude, and pace of secular trends in body height, weight, and body mass index (BMI) among Chinese urban students aged 7-18 years from 2000 to 2019.

METHODS

Data were extracted from Chinese urban students aged 7-18 years from the Chinese National Surveillance on Students' Constitution and Health in 2000, 2005, 2010, 2014, and 2019. The height, weight, and BMI of 548 419, 548 408, and 548 365 urban students aged 7-18 years, respectively, were tested. The mean differences across survey years were tested by one-way analysis of variance (ANOVA). The pace of secular trends is expressed as the change every 5 years between every two adjacent survey years.

RESULTS

Height increments between 1.9 and 6.2 cm, weight increments between 2.7 and 8.6 kg, and BMI increments between 0.9 and 1.9 kg/m2 were observed in boys. For girls, height increments between 1.5 and 4.9 cm, weight increments between 2.2 and 6.0 kg, and BMI increments between 0.7 and 1.7 kg/m2 were observed. The pace of secular trends in height decreased in the last 5 years, and the secular trends in weight and BMI have accelerated in the last 9 years compared with the previous 10 years.

CONCLUSIONS

Although the secular trend in height among Chinese urban students has slowed, it has not yet reached its genetic potential and continues to increase. The rapid increase in weight and BMI was a cause for concern. Our findings provide a basis for the future formulation of public health interventions in China.

Metabolically healthy obesity and left ventricular geometric remodelling in Chinese children

AIM

To investigate the association between metabolically healthy obesity (MHO) and left ventricular geometric remodelling in Chinese children.

MATERIALS AND METHODS

This cross-sectional study used data from two population-based samples in China, including 2871 children aged 6-11 years. Weight status was defined based on body mass index according to the World Health Organization growth chart. Metabolic status was defined based on the 2018 consensus-based criteria proposed by Damanhoury et al. Obes Rev 2018;19:1476-1491 (blood pressure, lipids and glucose). Left ventricular geometric remodelling was determined as concentric remodelling, eccentric hypertrophy, and concentric hypertrophy. Multinomial logistic regression analysis was used to determine odds ratios (ORs) and 95% confidence intervals (CIs) for the association between categories of weight and metabolic status and left ventricular geometric remodelling.

RESULTS

Compared with children with metabolically healthy normal weight, those with MHO had higher odds of left ventricular geometric remodelling, with adjusted ORs (95% CIs) of 2.01 (1.23-3.28) for concentric remodelling, 6.36 (4.03-10.04) for eccentric hypertrophy, and 17.07 (7.97-36.58) for concentric hypertrophy. Corresponding ORs (95% CIs) were 2.35 (1.47-3.75), 10.85 (7.11-16.55), and 18.56 (8.63-39.94), respectively, for children with metabolically unhealthy obesity. In contrast, metabolically unhealthy normal weight was not associated with higher odds of left ventricular geometric remodelling. Findings were consistent in sensitivity analyses that used different definitions of weight and metabolic status and left ventricular geometric remodelling.

CONCLUSIONS

Children with MHO had higher odds of left ventricular geometric remodelling than their metabolically healthy normal weight counterparts. Our findings suggest MHO may not be a benign condition for cardiac health in children.

Temporal changes in the physical fitness of Chinese adolescents aged 13-18 years: an analysis of eight national successive surveys over three decades

Objective

The aim of this study was to assess temporal changes in physical fitness of Chinese adolescents aged 13-18 years from 1985 to 2019.

Methods

Body size /composition and physical fitness indicators, including body height, weight, body mass index (BMI), speed, power, flexibility, muscular endurance, and cardiorespiratory fitness (CRF), were selected from Chinese boys and girls aged 13-18 years from eight Chinese National Surveillance on Students' Constitution and Health from 1985 to 2019. Temporal changes in means were estimated by sample-weighted linear regression at the test × sex × age level, and national trends were estimated by a post-stratification population weighting procedure.

Results

Overall mean body height, weight and BMI increased significantly for Chinese adolescents over 34 years. There was a small improvement for boys in speed (Effect size [ES] = -0.21, 95% confidence interval [CI] = -0.44 ~ 0.02), a small improvement for boys in power (ES = 0.24, 95% CI = -0.20 ~ 0.69), a small improvement for girls in flexibility (ES = 0.45, 95% CI = 0.15 ~ 0.76), a moderate decline for boys (ES = -0.53 95% CI = -0.84 ~ -0.21) and a moderate improvement for girls (ES = 0.61, 95% CI = -0.03 ~ 1.26) in muscular endurance, and large declines in cardiorespiratory fitness (CRF) for boys (ES = 0.93, 95% CI = 0.64 ~ 1.21) and girls (ES = 0.93, 95% CI = 0.58 ~ 1.27) from 1985 to 2019. These trends in each component of fitness were more positive for adolescents aged 13-15 years than that of adolescents aged 16-18 years in both sexes, except for girls in flexibility.

Conclusion

The decline in CRF was most pronounced among Chinese children and adolescents from 1985 to 2019, suggesting a future decline in population health that needs attention.

Low Body Fat Percentage and Menstrual Cycle Disorders in Female Elite Adolescent Dancers

Introduction: The menstrual cycle is an important indicator of health in female athletes. Female elite adolescent dancers are expected to control their weight while also training intensely, which can lead to menstrual disorders. This study aimed to investigate the relationship between body composition and menstrual status in female elite adolescent dancers. Methods: In total, 131 female elite adolescent dancers (age: 15.9 ± 1.5 years) were enrolled in this study. We measured the height, weight, and body fat percentage (BFP) for each participant and calculated their body mass index (BMI). We gathered information on individual menstruation patterns and the participants' menstrual cycles over the previous year using recall methods. We then compared the differences between dancers with menstrual cycle disorders and those without. Primary amenorrhea was defined as menarche occurring after the age of 15, while secondary amenorrhe was defined as experiencing fewer than 5 or no menstrual periods for at least 3 of the previous 12 months. We conducted a reliability test using the same questionnaire 2 weeks later. Statistical significance was defined as P < .05, and we calculated the effect sizes (d) and 95% confidence intervals (95% CI). Results: The average BMI and BFP were 22.6 ± 3.0% and 19.4 ± 2.2 kg/m2, respectively. Low BFP and low BMI were observed in 51 (38.6%) and 47 (35.6%) participants, respectively. Primary amenorrhea in 3 participants (2.3%) and 29 (22.1%) reported experiencing secondary amenorrhea; they had lower BFP than the dancers who did not experience amenorrhea (P = .041, 95% CI, -2.51 to -0.05). Conclusion: Female elite adolescent dancers in China may have lower BFP and menstrual problems. Given that lower BFP may contribute to the occurrence of menstruation disorders, it is essential to pay an attention to both BFP and the menstruation status in female elite adolescent dancers.

Temporal trends and distributional changes in cardiorespiratory fitness among Chinese children and adolescents from 1985 to 2019

OBJECTIVES

The aim of this study was to analyze the temporal trends in cardiorespiratory fitness (CRF) and body mass index (BMI) among children and adolescents from 1985 to 2019.

METHODS

A total of 1 840 212 children and adolescents aged 7-18 years (921 223 boys) were tested for CRF from 1985 to 2019. CRF was tested by 50-m × 8 shuttle run for boys and girls aged 7-12 years, 1000-m run for boys aged 13-18 years, and 800-m run for girls aged 13-18 years. Trends in BMI from 2000 to 2019 were also investigated.

RESULTS

Cardiorespiratory fitness decreased during the entire 34 years among children and adolescents in all sex and age categories, and the most rapid decline occurred from 1995 to 2005. Some positive trends in CRF were observed among adolescents aged 13-15 years from 2005 to 2019 and among girls aged 16-18 years from 2014 to 2019. The variation in the CRF distribution was not uniform, with Z-scores for participants with high CRF levels changing little or increasing (CRF stabilized or improved) and Z-scores for participants with low CRF levels continuing to decrease (CRF decreased). BMI increased over time for boys and girls in all age categories, with an acceleration of the increase for adolescents in recent years.

CONCLUSIONS

This study revealed that the overall CRF levels of Chinese children and adolescents decreased over three decades but stabilized or improved in recent years. BMI continued to increase. Our findings are important for the focus on future domestic physical fitness and public health.

Association between BMI and age at menarche or spermarche among both sexes: Findings from six successive national surveys in China

Background

To explore trends of the association between body mass index (BMI) and age at menarche or spermarche and its urban-rural disparities from 1995 to 2019.

Methods

A total of 912 753 children and adolescents - including 519 940 9-18 years old girls and 392 813 11-18 years old boys - were involved in six successive cross-sectional surveys conducted across 30 provinces in China from 1995 to 2019. Data on menarche and spermarche was collected using the status quo method, where same-gender physicians conducted face-to-face interviews to determine if children and adolescents had experienced their first menstrual cycle or ejaculation (yes/no). The median age at menarche or spermarche was estimated by probit analysis. Anthropometric measurements measured the height and weight of the study subjects. Children and adolescents were classified into thinness, normal range of weight, overweight, and obesity. t test was used to compare the differences in BMI between premenarchal and postmenarchal girls or prespermarcheal and postspermarcheal boys. Logistic regression was used to explore the associations between BMI/nutritional status and menarche or spermarche stratified by urban or rural residency status.

Results

From 1995 to 2019, BMI in all age groups growth over time, and the values of BMI among children and adolescents under 15 who had menarche or spermarche were more significant than those without menarche or spermarche. In 2019, for girls, thinness was associated with delayed menarche (odds ratio (OR) = 0.26; 95% confidence interval (CI) = 0.24-0.28), while overweight (OR = 1.99; 95% CI = 1.85-2.14) and obesity (OR = 2.20; 95% CI = 1.92-2.53) was associated with advanced menarche. For boys, thinness was associated with delayed spermarche (OR = 0.71; 95% CI = 0.65-0.78), overweight was associated with advanced spermarche (OR = 1.08; 95% CI = 1.01-1.15) while obesity had no association with spermarche. The OR between BMI and menarche in 1995 was 1.35 (95% CI = 1.33-1.37), which decreased to 1.19 (95% CI = 1.18-1.20) by 2019. The OR between BMI and spermarche in 1995 was 1.10 (95% CI = 1.09-1.11), which decreased to 1.02 (95% CI = 1.02-1.03) by 2019. The trends by urban-rural stratification were consistent with the total sample.

Conclusions

We have established a dose-response relationship between BMI and menarche in girls, whereas the association appears to be nonlinear in boys, and the associations were diminishing. Similar findings were observed in both urban and rural areas. Considering the dual adverse effects of obesity and early puberty on health, the results of this study suggest that sexual health education should be strengthened, especially among obese girls. Further research on the influencing factors and biological mechanisms of early puberty will be beneficial.

Long-term exposure to ambient PM2.5 and its components on menarche timing among Chinese adolescents: evidence from a representative nationwide cohort

BACKGROUND

Ambient air pollutants have been suggested to affect pubertal development. Nevertheless, current studies indicate inconsistent effects of these pollutants, causing precocious or delayed puberty onset. This study aimed to explore the associations between long-term exposure to particulate matter with aerodynamic diameters ≤ 2.5 μm (PM2.5) along with its components and menarche timing among Chinese girls.

METHOD

Self-reported age at menarche was collected among 855 girls from China Health and Nutrition Survey 2004 to 2015. The pre-menarche annual average concentrations of PM2.5 and its components were calculated on the basis of a long-term (2000-2014) high-resolution PM2.5 components dataset. Generalized linear models (GLM) and logistic regression models were used to analyze the associations of exposure to a single pollutant (PM2.5, sulfate, nitrate, ammonium, black carbon and organic matter) with age at menarche and early menarche (< 12 years), respectively. Weighted quantile sum methods were applied to examine the impacts of joint exposure on menarche timing.

RESULTS

In the adjusted GLM, per 1 µg/m3 increase of annual average concentrations of nitrate and ammonium decreased age at menarche by 0.098 years and 0.127 years, respectively (all P < 0.05). Every 1 µg/m3 increase of annual average concentrations of PM2.5 (OR: 1.04, 95% CI: 1.00-1.08), sulfate (OR: 1.23, 95% CI: 1.01-1.50), nitrate (OR: 1.23, 95% CI: 1.06-1.43) and ammonium (OR: 1.32, 95% CI: 1.06-1.66) were significantly positively associated with early menarche. Higher level of joint exposure to PM2.5 and its components was associated with 11% higher odds of early menarche (P = 0.04). Additionally, the estimated weight of sulfate was the largest among the mixed pollutants.

CONCLUSIONS

Long-term exposure to PM2.5 and its components could increase the risk of early menarche among Chinese girls. Moreover, sulfate might be the most critical components responsible for this relationship. Our study provides foundation for targeted prevention of PM2.5 components.

Prediction of body mass index and skeletal maturity for early menarche risk at menarche onset: a cross-sectional study of Chinese girls

BACKGROUND

This study aimed to assess the predictive value of body mass index (BMI) and skeletal maturity for the occurrence of early menarche in Chinese girls.

METHODS

A cross-sectional analysis was conducted on 785 girls aged 8.1-14.6 years who visited our hospital within 3 months of menarche onset. Early menarche was defined as menarche age (MA) <10 years. Skeletal maturity was classified based on the difference between bone age (BA) and chronological age (CA), termed BA-CA; advanced BA was defined as BA-CA>2 years.

RESULTS

The average MA was 10.7 (SD: 1.1) years, with a prevalence of early menarche of 23.3%. BA exhibited relative stability compared with MA, with an average of 12.8 (SD: 0.5) years at menarche onset. At menarche onset, the average height, weight and BMI were 149.1 (SD: 5.1) cm, 43.3 (SD: 7.2) kg and 19.4 (SD: 2.8) kg/m², respectively. Logistic regression analyses indicated that every 1-year increment in BA-CA was independently associated with a 18.90-fold higher risk of early menarche (95% CI 11.77 to 30.32), respectively, and remained statistically significant even after adjusting for height or mid-parental height. Furthermore, the prediction of BA-CA for early menarche demonstrated a dose-dependent pattern across BMI categories, with the greatest risk observed in normal-weight girls, the lowest risk in obese girls and an intermediate risk in overweight girls at the same degree of BA advancement.

CONCLUSIONS

Our findings provide evidence supporting the significant contributions of BMI and skeletal maturity in predicting early menarche among Chinese girls at menarche onset. Additionally, the results suggest a dose-dependent relationship between skeletal maturity and BMI categories, with normal-weight girls displaying a higher risk of early menarche compared to overweight and obese girls with the same degree of BA advancement.

Trend and heterogeneity in forced vital capacity among Chinese students during 1985-2019: results from Chinese National Survey on Students' Constitution and Health

BACKGROUND

Forced vital capacity (FVC) reflects respiratory health, but the long-term trend and heterogeneity in FVC of Chinese students were understudied.

METHODS

Data were from Chinese National Survey on Students' Constitution and Health 1985-2019. Super Imposition by Translation and Rotation model was used to draw FVC growth curves. Sex-, region-, and nationality-heterogeneity in FVC was evaluated. Spearman correlation and generalized additive model was used to reveal influencing factors for FVC.

RESULTS

Compared to 1985, age at peak FVC velocity was 1.09, 3.17, 0.74, and 1.87 years earlier for urban male, urban female, rural male, and rural female in 2019, respectively. Peak FVC velocity first decreased and then increased during 1985-2019, only male rebounded to larger than 1985 level. FVC declined from 1985 to 2005 and then raised. Males consistently had higher FVC than females, with disparities increasing in the 13-15 age group. Urban students also had higher FVC than rural students. In 2019, FVC difference between 30 Chinese provinces and the national average showed four scenarios: consistently above national average; less than national average until age 18, then above; greater than national average until age 18, then this advantage reversed; less than national average in almost all the age. Most Chinese ethnic minority students had lower FVC levels compared to Han students. Spearman correlation and generalized additive model showed that age, sex, and height were the leading influencing factors of FVC, followed by socioeconomic and environmental factors.

CONCLUSIONS

Chinese students experienced advanced FVC spurt, and there was sex-, region- and nationality-heterogeneity in FVC. Routine measurement of FVC is necessary in less developed areas of China.

Long-term trends and urban-rural disparities in the physical growth of children and adolescents in China: an analysis of five national school surveys over three decades

BACKGROUND

China's rapid economic growth has brought opportunities for improved health and growth of children and adolescents. We sought to explore the long-term trends and urban-rural inequalities in physical growth (specifically height and BMI) among school-aged children and adolescents in China to identify policy priorities for a healthier generation.

METHODS

We used the 1985, 1995, 2005, 2014, and 2019 cycles of the Chinese National Survey on Students' Constitution and Health from primary and secondary schools in 30 mainland provinces, autonomous regions, and municipalities. We analysed height and BMI data for 7, 12, and 18 year old children and adolescents of Han ethnicity. Children and adolescents who had complete data on age, sex, location, weight, and height were included. All surveys used a multi-stage stratified random cluster sampling method and were nationally representative. A univariate kernel density estimation was used to plot the distribution of height and BMI. Quantile regression was used to examine associations between urban and rural locations and the primary outcomes of height and BMI at specific quantiles of distribution (5th, 25th, 50th, 75th, and 95th).

FINDINGS

Across the five surveys (in 1985, 1995, 2005, 2014, and 2019), 313 973 children and adolescents were included. From 1985 to 2019, the height and BMI distribution curves shifted to the right for each age group and sex, with the BMI curve becoming more dispersed. Median height in adolescents aged 18 years increased by 3·8 cm (95% CI 3·4-4·1) in boys in urban areas and 5·7 cm (5·3-6·1) in boys in rural areas, and 2·7 cm (2·4-3·0) in girls in urban areas and 3·7 cm (3·4-4·0) in girls in rural areas. Children in urban areas were taller than those in rural areas at every quantile, but the magnitude of this disparity narrowed by 2019. In 2019, the median height of boys in urban areas were 1·4 cm (1·0-1·8) greater in those aged 7 years, 2·5 cm (1·9-3·1) greater in those aged 12 years, and 1·1 cm (0·6-1·5) greater in those aged 18 years than their rural counterparts, whereas the median height of girls in urban areas were 1·1 cm (0·7-1·4) greater in those aged 7 years, 1·6 cm (1·1-2·1) greater in those aged 12 years, and 1·1 cm (0·7-1·5) greater in those aged 18 years than rural girls. Over this period, urban-rural differences in BMI disappeared at the lowest quantile, but persisted at higher quantiles. In 2019, the urban-rural differences in BMI for boys aged 12 years were 0·6 kg/m2 (95% CI 0·3-0·8) at the median, 1·0 kg/m2 (0·6-1·4) at the 75th quantile, and 0·7 kg/m2 (0·1-1·3) at the 95th quantile; for girls aged 12 years, 0·3 kg/m2 (0·1-0·5) at the median, 0·5 kg/m2 (0·2-0·8) at the 75th quantile, and 0·9 kg/m2 (0·3-1·5) at the 95th quantile; for boys aged 18 years, 0·6 kg/m2 (0·4-0·8) at the median, 0·8 kg/m2 (0·5-1·2) at the 75th quantile, and 0.7 kg/m2 (0·0-1·5) at the 95th quantile; and for girls aged 18 years, 0·2 kg/m2 (0·1-0·4) at the median, 0·5 kg/m2 (0·3-0·8) at the 75th quantile, and 1·0 kg/m2 (0·5-1·5) at the 95th quantile.

INTERPRETATION

Across three decades, school-aged children and adolescents in China have increased in height and BMI, with less disparity between urban and rural locations. Investments are needed to improve the affordability of healthy foods to help children and adolescents in rural areas reach their potential maximum height. Meanwhile, these changes in BMI necessitate tailored strategies according to urban-rural settings to contain the increase in overweight and obesity and promote optimal growth for children and adolescents.

FUNDING

Capital's Funds for Health Improvement and Research, and National Natural Science Foundation of China.