Background: Childhood obesity is a serious public health concern. School-based interventions hold great promise to combat the rising trend of childhood obesity. This systematic review aimed to assess the overall effects of school-based obesity prevention interventions, and to investigate characteristics of intervention components that are potentially effective for preventing childhood obesity. Methods: We systematically searched MEDLINE, CENTRAL and Embase databases to identify randomized- or cluster randomized- controlled trials of school-based obesity interventions published between 1990 and 2019. We conducted meta-analyses and subgroup analyses to determine the overall effects of obesity prevention programs and effect differences by various characteristics of intervention components on body mass index (BMI) or BMI Z-score of children. Results: This systematic review included a total of 50 trials (reported by 56 publications). Significant differences were found between groups on BMI (− 0.14 kg/m² (95% confidence interval: − 0.21, − 0.06)) and BMI Z-score (− 0.05 (− 0.10, − 0.01)) for single-component interventions; significant differences were also found between groups on BMI (− 0.32 (− 0.54, − 0.09) kg/m²) and BMI Z-score (− 0.07 (− 0.14, − 0.001)) for multi-component interventions. Subgroup analyses consistently demonstrated that effects of single-component (physical activity) interventions including curricular sessions (− 0.30 (− 0.51, − 0.10) kg/m² in BMI) were stronger than those without curricular sessions (− 0.04 (− 0.17, 0.09) kg/m² in BMI); effects of single-component (physical activity) interventions were also strengthened if physical activity sessions emphasized participants’ enjoyment (− 0.19 (− 0.33, − 0.05) kg/m² in BMI for those emphasizing participants’ enjoyment; − 0.004 (− 0.10, 0.09) kg/m² in BMI for those not emphasizing participants’ enjoyment). The current body of evidence did not find specific characteristics of intervention components that were consistently associated with improved efficacy for multi-component interventions (P > 0.05). Conclusions: School-based interventions are generally effective in reducing excessive weight gain of children. Our findings contribute to increased understandings of potentially effective intervention characteristics for single-component (physical activity) interventions. The impact of combined components on effectiveness of multi-component interventions should be the topic of further research. More high-quality studies are also needed to confirm findings of this review.

Numerous studies have demonstrated that exposure to ambient ozone (O₃) could have adverse effects on children’s respiratory health. However, previous studies mainly focused on asthma and wheezing. Evidence for allergic rhinitis and bronchitic symptoms (e.g., persistent cough and phlegm) associated with O₃ is limited, and results from existing studies are inconsistent. This study included a total of 59,754 children from the seven northeastern cities study (SNEC), who were aged 2 to 17 years and from 94 kindergarten, elementary and middle schools. Information on doctor-diagnosed allergic rhinitis (AR), persistent cough, and persistent phlegm was collected during 2012–2013 using a standardized questionnaire developed by the American Thoracic Society (ATS). Information for potential confounders was also collected via questionnaire. Individuals’ exposure to ambient ozone (O₃) during the four years before the investigation was estimated using a satellite-based random forest model. A higher level of O₃ was significantly associated with increased risk of AR and bronchitic symptoms. After controlling for potential confounders, the OR (95% CI) were 1.13 (1.07–1.18), 1.10 (1.06–1.16), and 1.12 (1.05–1.20) for AR, persistent cough, and persistent phlegm, respectively, associated with each interquartile range (IQR) rise in O₃ concentration. Interaction analyses showed stronger adverse effects of O₃ on AR in children aged 7–17 years than those aged 2–6 years, while the adverse association of O₃ with cough was more prominent in females and children aged 7–12 years than in males and children aged 2–6 and 13–17 years. This study showed that long-term exposure to ambient O₃ was significantly associated with higher risk of AR and bronchitic symptoms in children, and the association varies across age and gender. Our findings contribute additional evidence for the importance of controlling O₃ pollution and protecting children from O₃ exposure.

Early life nutritional exposures could modify the gene expression and susceptibility of allergic diseases (AD). This systematic review aimed to evaluate whether early life (the first 1,000 days) natural exposure to polyunsaturated fatty acids (PUFA) and ruminant trans fatty acids (R-TFA) could affect the AD risk. We searched PubMed, EMBASE, PsycINFO, Scopus, the Cochrane Library, and ClinicalTrials.gov from inception through September 10, 2017 for relevant full-text articles in English. Observational studies were selected if they examined the effects of early life PUFA or R-TFA on AD (eczema, asthma, wheeze, and allergic rhinitis) or sensitization. The quality of studies was examined by the Newcastle-Ottawa Scale, and the best evidence synthesis (BES) was applied. We included 26 observational studies, and 8 of them showed high quality. BES showed a moderate evidence for the protective effect of vaccenic acid (VA, an R-TFA) on eczema, while insufficient or no evidence was found in other associations. Meta-analysis showed that higher n-6/n-3 ratio and linoleic acid were associated with higher risk of eczema (pooled odds ratio [OR] = 1.06, 95% confidence intervals [CI]: 1.00 −1.13; 1.08, 95% CI: 1.01 −1.15). However, VA was inversely associated with eczema pooled OR = 0.42, 95% CI: 0.25 −0.72). Early life natural exposure to VA showed evident benefit on decreasing the risk of eczema, while PUFA and other R-TFA showed limited effects on AD. More robust studies especially for R-TFA are required.

Evidence from animal experiments has shown that chlorinated polyfluoroalkyl ether sulfonic acids (Cl-PFESAs) can induce vision dysfunction in zebrafish. However, environmental epidemiological evidence supporting this hypothesis remains limited. In our case-control study, samples collected from 270 individuals (135 controls and 135 cases) from the Isomers of C8 Health Project data were analyzed for Cl-PFESAs. We also repeated our analysis on zebrafish to support our findings in humans and to decipher the mechanism underlying Cl-PFESA eye toxicity. The serum levels of per- and polyfluoroalkyl substances (PFASs) and alternatives were significantly higher in the cases than in the controls. Higher serum Cl-PFESA levels were associated with greater odds of eye diseases, and the trend showed a statistically significant dose-dependent relationship. The Shapley additive explanations (SHAP) value indicated that 8:2 Cl-PFESA was the dominant eye disease risk factor among the 13 studied PFASs. In zebrafish experiments, Cl-PFESAs induced eye toxicity in adult zebrafish by oxidative damage and cell apoptosis. Compared to the control group, there was significantly reduced thicknesses of the inner plexiform layer (IPL), outer plexiform layer (OPL), and retinal tissue in the zebrafish exposed to Cl-PFESAs. Our study provides human clinical and animal experimental data, showing that exposure to PFASs increases the odds of the development of eye toxicity.