Original ResearchIncreased obesity risks for being an only child in China: findings from a nationally representative study of 19,487 children
Introduction
As the largest developing country, China has seen a rapid increase in childhood obesity over the past several decades: the combined prevalence of childhood overweight and obesity has increased from 2% in 1981–1985 to 21% in 2006–2010,1 and in some major cities, it has reached above 30% among boys, which is even higher than that in the US.2 Effective interventions are urgently needed.
Family is a critical setting for intervention. Family structure was identified as a key factor affecting children's weight status.3, 4 Studies have consistently reported that being the only child in the family is associated with increased risks of overweight or obesity.5, 6, 7, 8, 9, 10 Only-child status seems to have a dose-response effect: longer duration of being the only child in the family is associated with higher overweight risk.6, 7
Given its large population base, rapid demographic transition, and 30-year one-child policy, China has the largest only-child population in the world (≈100 million).11 Only children in China were often viewed as overweight ‘little emperors’ over-nourished by doting parents and grandparents.12, 13, 14 Accordingly, the one-child policy was often cited as a leading contributor to the rising child obesity epidemic,15 although very few studies have evaluated the obesity risk among only children in China and, among two notable exceptions, null findings were reported.16, 17 Neither study, however, used nationally representative data or considered possible gender and urban-rural variations in the association. Moreover, both studies used conventional regression adjustment in dealing with potential confounding effects, which relies on an untestable assumption about correct model specification. To reduce bias due to potential model misspecification, methods with more robust properties should be used to obtain more precise estimates.
Furthermore, to our knowledge, no study has examined how only-child status may affect energy expenditure–related behaviors among Chinese children. Accordingly, little is known about lifestyle factors that may put only children at increased risks of overweight or obesity.
The present study examined the associations of only-child status with weight status and several energy expenditure–related behaviors based on data from the most recent national data. We also examined how such associations may vary by sex and region. To reduce bias due to confounding and/or potential model misspecification, our estimation followed a combined strategy of propensity score weighting and multilevel regression, which provides a doubly robust estimator yielding consistent estimates if only either the outcome regression model or the propensity score model was correctly specified.18 Findings from this study will inform family-based interventions and projections of future obesity trend in China.
Section snippets
Data and study population
Analyses were done based on data from the baseline wave (2013–2014) of the China Education Panel Survey-Junior High Cohorts (CEPS-JH). Following a stratified multistage sampling design, CEPS-JH is an ongoing panel study of a nationally representative sample of 10,279 seventh grade and 9208 ninth grade students, from 112 schools located in 28 regions across in China. Separate questionnaires were administered to students, parents, teachers, and school principals to collect multilevel information
Characteristics of only- and sibling-children
Overall, 32.9% of all study participants were only children. The percentage of only children significantly varied according to their demographic characteristics (Table 1): it was higher among boys (36.6%, vs 28.7% for girls), urban families (53.6%, vs 21.3% for rural families), the majority ethnic group (36%, vs 15.5% for ethnic minorities), non-migrant families (33.3%, vs 29.2% for migrant families), and families with higher SES (as was indicated by higher parental education, more prestigious
Discussion
Given the rapid demographic transition and obesity growth in China, it is important to study whether the large only-child population might contribute to the obesity epidemic. Based on the first nationally representative data and propensity score weighting method, we found that only child status is a potential risk factor for overweight/obesity, particularly for urban boys. For rural boys, no significant difference in weight status existed between only children and sibling children. For girls,
Ethical approval
The data collection of the China Education Panel Survey-Junior High was approved by the Institutional Review Board at the Renmin University of China. Written informed consent was obtained from study participants.
Funding
The study is funded in part by the US National Institute of Health (NIH, U54 HD070725). The U54 center project is funded by The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) and the Office of the Director, National Institutes of Health (OD).
Competing interests
The
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