Cohort profile: Aichi regional sub-cohort of the Japan Environment and Children's Study (JECS-A)

Associations of 1.5- and 3-year phthalate exposure levels with early adiposity rebound and overweight/obesity in Japanese children: An adjunct study of the Japan Environment and Children's Study

The relationship between early childhood phthalate exposure and early adiposity rebound (EAR) is unclear. This study aimed to investigate the association between 1.5- and 3-year phthalate exposure and EAR and overweight/obesity in 7.5-year-old Japanese children. A total of 452 mother-child pairs were enrolled from the Aichi Regional Cohort of the Japan Environment and Children's Study. The children were followed up at birth and at 1.5, 2, 3, 4, 5, 6, and 7.5 years of age for physical examination. Human biomonitoring of 16 urinary metabolites of eight phthalates was performed at 1.5 and 3 years of age. Latent class mixed models, binary logistic regression, and quantile g-computation were performed to identify body mass index (BMI) trajectories and investigate the relationships of single or mixed phthalate exposure with EAR and overweight/obesity. A one-unit increase in log10-transformed 3-year-old Σdi(2-ethylhexyl) phthalate (ΣDEHP) exposure levels was significantly associated with 6-year-old BMI in girls. The 1.5-year mono-iso-butyl phthalate and 3-year Σdi-isodecyl phthalate exposure levels were significantly associated with the repeated measures of longitudinal BMIs in girls. Single phthalate exposure showed null associations with EAR or overweight/obesity in the 7.5-year-old children. Σdi-isononyl phthalate, ΣDEHP, and mono-n-butyl phthalate exhibited the highest proportion of partial positive weights of being in the EAR trajectory after confounder adjustment. Phthalate mixture exposure in 1.5- and 3-year-old children was not significantly associated with EAR. Early childhood phthalate exposure was not related to EAR or overweight/obesity in 7.5-year-old Japanese children. However, few phthalates were positively associated with longitudinal BMIs in girls.

Investigating the link between temperamental and motor development: a longitudinal study of infants aged 6-42 months

BACKGROUND

Since the 1920s, motor development has been a strong research theme, focusing on infants' acquisition of motor skills, such as turning over and crawling. In the 1980s, a dynamic systems approach began emphasizing children's own motivation, which helped explain individual differences in the emergence of motor skills. However, few studies have examined factors contributing to individual differences in early motor development. In response, we investigated directional associations between temperament and motor development in children aged 6 months to 3 years.

METHOD

The Japan Environment and Children's Study (JECS-A) recruited mothers between January 2011 and March 2014. 2,639 mothers were sent a questionnaire at 6 months, and responses were received from 1,657 of them, with full data for children aged 6 months, 2 years, and 3 years, including from three mothers of twins, were analyzed through structural equation modeling. Question items regarding fine and gross motor activities at each age were selected by pediatric neurologists specializing in developmental disorders. The Japanese version of the Little Developmental Coordination Disorder Questionnaire was administered at 42 months. Temperament was assessed through the parent-reported Behavior Questionnaire (short version) for infants, toddlers, and children. In all three measures, Surgency and Negative Affectivity were extracted, and Effortful Control, a major form of self-regulation, was found from toddlerhood onward, as in previous studies.

RESULTS

A path diagram reveals that at 6 months, Surgency and Orienting/Regulation interacted positively with the motor function (respectively, r = .57; r = 40, ps < .001). Up to about 3 years, Effortful Control plays a role in facilitating the motor function, resulting in positive effects on Control During Movement (CDM), General Coordination (GC), and Fine Motor Movement (FMM) (β = 14; β = 30; β = 37, ps < .001). Surgency had a positive effect on CDM and GC (β = 18; β = 06, ps < .001), whereas Negative Affect had a negative influence on FMM and GC (β = -.08; β = -.08, ps < .001).

CONCLUSION

While Surgency may be a key reactive factor in early motor development, Effortful Control and Movement develop in an interactive manner.

TRIAL REGISTRATION

UMIN000030786. Scientific Title: The Japan Environment and Children's Study. Date of disclosure of the study: 2018/01/15. Only questionnaires were administered in the study.

Development of temperamental regulation of infants at 6 and 24 months: Associations with maternal soothing and distress

Background and Aims

In the neurobiological theory of attention, the orienting network mainly supports the temperamental regulatory function in infancy, with soothing methods such as visual attention distraction influencing its development. The attention distraction method chosen for soothing is thought to be influenced by maternal sensitivity, which has been found to decrease with poor maternal mental health. We hypothesize that the degree of maternal distress may affect the choice of attention distraction soothing method. Further, individual differences in being soothed by attention distraction will be associated with the temperamental regulation function in infancy/toddlerhood.

Method

Structural equation modeling (SEM) was conducted on longitudinal data at 6 and 24 months on a sample (N = 1892) drawn from the sub-cohort of the Japan Environment and Children's Study (JECS). Temperament was examined through the short Infant Behavior Questionnaire-Revised (Japanese version) and the Early Childhood Behavior Questionnaire (Japanese version). Distress in caregivers was measured through the Kessler Psychological Distress Scale (Japanese version) at prenatal and 1-year-postnatal stages. Individual differences in using visual distraction soothing methods were also measured using tailor-made items.

Results

Postnatal maternal distress at 12 months was negatively related to the tendency to use visual attention distraction as a soothing method (β = -0.06, p = 0.006) at 24 months. When we applied the subscale of the temperamental regulatory factor in SEM, the more the mothers chose the distraction method for soothing, i.e., the more the toddlers experienced it, the higher their attention shifting scores (β = 0.07, p = 0.002).

Conclusion

The findings support the view that caregivers' choice of method for distracting offspring's attention from distress may be associated with the development of self-regulation during infancy and toddlerhood.

Oral hygiene status and vascular aging in schoolchildren and their mothers

BACKGROUND

Poor oral hygiene, generally manifesting as dental caries, gingivitis, or periodontitis, is a common chronic condition among both children and adults worldwide and has been reportedly associated with hypertension and arterial stiffness mainly in adult patients. However, these associations have not been well-studied in children and adults in the general population. Therefore, we conducted this cross-sectional study to clarify the associations between oral hygiene indices and high blood pressure (BP)/hypertension and arterial stiffness as assessed by the cardio-ankle vascular index (CAVI) in children along with their mothers. The association between maternal oral hygiene and high BP in children was also examined based on the hypothesis that maternal awareness of oral hygiene is related to their children's oral hygiene.

METHODS

This study was conducted as an Adjunct Study of the Aichi Regional Sub-Cohort of the Japan Environment and Children's Study. Participating children (n = 220, 85-104 months old) and their mothers (n = 217, 29-52 years old) underwent dental/intra-oral examination and BP and CAVI assessment. High BP in children and hypertension in mothers were diagnosed according to corresponding American guidelines. Logistic regression analysis or analysis of covariance was used to examine the associations of poor oral hygiene indices with BP and CAVI.

RESULTS

Maternal dental caries ≥1 was associated with their hypertension (adjusted odds ratio [aOR]: 2.72, 95% confidence interval (CI): 1.12-6.61). Maternal dental plaque ≥1/3 was associated with maternal hypertension and children's high BP (aOR, 95% CI: 4.71, 1.33-16.73 and 5.67, 1.22-25.04, respectively). Maximum pocket depth ≥4 mm was associated with children's high BP (aOR: 6.85, 95% CI: 1.24-38.01). No associations were observed between oral hygiene indices and CAVI in children; however, there was a significant association between dental plaque and CAVI in mothers (F = 5.62, p < 0.01).

CONCLUSIONS

The small sample size, especially the case number, made it necessary to refrain from drawing unambiguous conclusion. The hypothesis that warrants further investigation based on the present study results is that poor oral hygiene is associated with high BP in children and hypertension and arterial stiffness in mothers, and maternal oral hygiene is associated with high BP in children.

Quantitative Measurement of Phthalate Exposure Biomarker Levels in Diaper-Extracted Urine of Japanese Toddlers and Cumulative Risk Assessment: An Adjunct Study of JECS Birth Cohort

Phthalate exposure monitoring and risk assessment in non-toilet-trained children are rarely reported. This adjunct study of the Japan Environment and Children's Study assessed cumulative health risks in 1.5-year-old toddlers in the Aichi regional subcohort by biomonitoring 16 urinary metabolites of eight phthalate plasticizers. Overnight urine was extracted from toddlers' diapers (n = 1077), and metabolites were quantified using ultraperformance liquid chromatography coupled with tandem mass spectrometry. The analyses' quality was assured by running quality control samples. The highest geometric mean concentration was found for mono-(2-ethyl-5-carboxypentyl) phthalate, followed by mono-isobutyl phthalate (23 and 21 μg/L, respectively). Di-2-ethylhexyl phthalate (DEHP) and di-butyl phthalate exhibited higher risks [hazard quotient (HQ) > 1] than the cutoff level in a small proportion of toddlers; 8 and 14% of toddlers were at cumulative risk of multiple phthalates beyond the cutoff level [hazard index, (HI) > 1], based on the tolerable daily intake of the European Food Safety Authority and the United States Environmental Protection Agency Reference Dose. HI > 1 for antiandrogenicity in creatinine-unadjusted and -adjusted estimations were exhibited by 36 and 23% of the children, respectively. Thus, identifying exposure sources and mitigating exposure are necessary for risk management. Additionally, continuous exposure assessment and evaluation of health outcomes, especially antiandrogenic effects, are warranted.

Epidemiological Studies of Children's Gut Microbiota: Validation of Sample Collection and Storage Methods and Microbiota Analysis of Toddlers' Feces Collected from Diapers

The composition of human gut microbiota influences human health and disease over the long term. Since the flora in specimens can easily change at ambient temperature outside the body, epidemiological studies need feasible methods of stool specimen collection and storage to be established. We aimed to validate two methods: feces frozen-stored in tubes containing guanidine thiocyanate solution for two months after collection (Method B), and feces excreted in diapers and frozen-stored (Method C). Validation was by comparison with a gold standard Method A. Bacterial flora of five adults were sampled and stored by all three methods. Bacterial composition was examined by amplicon sequencing analysis. Bland-Altman analyses showed that Methods B and C might change relative abundances of certain bacterial flora. Thereafter, we analyzed the bacterial flora of 76 toddlers (two age groups) in stools sampled and processed by Method C. The diversity indices of toddlers' flora were less than those of adults. The relative abundance of some bacteria differed significantly between children aged 1.5 and 3 years. The specimen collection and storage methods validated in this study are worth adopting in large-scale epidemiological studies, especially for small children, provided the limited accuracy for some specific bacteria is understood.

Simultaneous quantification of pyrethroid metabolites in urine of non-toilet-trained children in Japan

Background

Pyrethroid (PYR) insecticides are widely used for controlling various pests. There are two types that differ in terms of usage: agricultural-purpose PYR (agriculture-PYR) and hygiene purpose PYR (hygiene-PYRs). Few studies exist on the exposure to these chemicals in small children. In this study, we conducted biomonitoring of urinary pyrethroid metabolites in 1.5-year-old children throughout the year.

Methods

Study subjects were 1075 children participating in an Aichi regional sub-cohort of the Japan Environment and Children’s Study as of 18-month health check-up. The concentrations of four specific hygiene-PYR metabolites including 2,3,5,6-tetrafluoro-1,4-benzenedimethanol (HOCH₂-FB-Al), and five common metabolites of hygiene- and agriculture-PYRs including 3-phenoxybenzoic acid (3PBA) and cis- and trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid (DCCA), were measured in urine samples extracted from soiled diapers using a triple quadrupole gas chromatograph-mass spectrometer.

Results

The highest detection frequencies were for 3PBA, followed by DCCA, 1R-trans-chrysanthemum dicarboxylic acid, and HOCH₂-FB-Al. Among the six metabolites, urinary concentrations were seasonally varied. However, this variation was not observed in the most studied PYR metabolite, 3PBA. Spearman’s correlation analysis demonstrated a significant positive correlation between FB-Al and DCCA (r = 0.56) and HOCH₂-FB-Al and 4-methoxymethyl-2,3,5,6-tetrafluorobenzyl alcohol (r = 0.60).

Conclusions

This biomonitoring survey found widespread and seasonally specific exposure to multiple hygiene- and agriculture-PYRs in 1.5-year-old Japanese children.

Cumulative exposure assessment of neonicotinoids and an investigation into their intake-related factors in young children in Japan

Exposure levels of neonicotinoids (NEO) in young children remain unknown, despite their widespread use and the plausible vulnerability of toddlers to environmental toxicants. Herein we aimed to clarify the exposure levels and sources of NEOs in young Japanese children. Disposable diapers were collected from 1036 children (16-23 months old) participating in an adjunct study of the Japan Environment and Children's Study between 2015 and 2016. Six NEOs and one metabolite in urine extracted from a diaper from each child were analyzed using high-performance liquid chromatography-tandem mass spectrometry. A relative potency factor approach was used to assess the cumulative exposure to NEOs equivalent to dinotefuran levels (DIN_RPF). The 95th percentile urinary concentration of DIN_RPF was 157 μg/L and 380 μg/g creatinine (Cr). Receiver operating characteristic curve analyses for the propensity scores of the possible exposure-related factors revealed that the discriminatory powers determining whether Cr-adjusted and Cr-unadjusted DIN_RPF concentrations exceeding the 95th percentile values were higher for the amount of each foodstuff ingested on the survey day (areas under the curve were 0.62 and 0.75, respectively) than for the exposure-related behaviors (0.60 and 0.71, respectively) or for mothers' attitudes toward food selection and preparation (0.54 and 0.57, respectively). Use of a mosquito coil, insect repellent, and mothproof net for a screen door, and playing on a lawn were associated with increased urinary NEO levels (odds ratio [OR]: 2.0-2.9), while care about the child's nutritional balance by mothers reduced urinary NEO levels (OR: 0.23-0.41). To the best of our knowledge, this is the first study that dealt with urinary concentrations and possible exposure sources of NEOs in a large number of young children. Attention to the children's behavior and diet might result in the reduction of a high exposure to NEOs in young children.

Sexual difference in 2nd-to-4th digit ratio among 1.5-year-old Japanese children: A cross-sectional study of Aichi regional adjunct cohort of the Japan Environment and Children's Study (JECS-A)

BACKGROUND

A sex difference in the second-to-fourth digit ratio (2D:4D, males < females) has been described in Japanese fetuses and children, and its possible links to autism spectrum disorders (ASDs) have been discussed. Accordingly, this sexual difference in representative neonates merits examination.

AIMS

This study aimed to examine 2D:4D measurements and sexual differences in Japanese toddlers aged 1.5 years.

STUDY DESIGN AND SUBJECTS

The digit lengths used to calculate 2D:4D were measured using an easy-to-use photography method. A total of 1045 JECS-A (the Aichi regional sub-cohort of the Japan Environment and Children's Study) children (males, 523; females, 522) aged 1.5 years were analyzed.

RESULTS

The mean ages for the males and females were 575.3 ± 13.1 and 575.9 ± 17.1 days, respectively. Histograms of left and right 2D:4D were normally distributed regardless of sex (left male, 0.909 ± 0.048; left female, 0.913 ± 0.049, d = 0.08; right male, 0.938 ± 0.055; right female, 0.937 ± 0.049, d = 0.02). Because of high dispersion in the data, t-tests did not support a significant sex difference in 2D:4D. Post-hoc statistical power was calculated as 0.124 and the effect size for the sex difference in 2D:4D was 0.036.

CONCLUSIONS

This study failed to confirm sexual differences in 2D:4D in 1.5-year-old Japanese children. This may be because digit measurement is difficult in this group, resulting in reduced effect sizes, or because rapid growth attenuates the in utero sexual dimorphism. This evidence is useful for the light it casts on the extreme male brain theory of ASDs.

Exposure levels of organophosphate pesticides in Japanese diapered children: Contributions of exposure-related behaviors and mothers' considerations of food selection and preparation

Organophosphate (OP) pesticide exposure is a public health issue due to its potential link to neurodevelopmental problems in children. This study aimed to examine the exposure levels of OP pesticides in Japanese toddlers and explore the possible contributions of their exposure-related behaviors and their mothers' considerations of food selection and preparation to their exposure levels to OP pesticides. We recruited diapered children participating in the Japan Environment and Children's Study and collected used disposable diapers from 1037 children between June 2015 and August 2016. Six dialkylphosphates (DAPs) were measured in the urine extracted from the diapers. The geometric means of urinary creatinine (Cr)-unadjusted and Cr-adjusted concentrations of the sum of the six DAPs (ΣDAP) were 120 nmol/L and 243 nmol/g Cr, respectively. A receiver operating characteristic curve analysis for propensity scores of exposure-related factors revealed that discriminatory powers determining whether Cr-unadjusted and Cr-adjusted ΣDAP concentrations exceeded the 95th percentile values were lower for the exposure-related behaviors (areas under the curve, 0.72 and 0.69, respectively) and the mothers' considerations of food selection and preparation (0.55 and 0.57, respectively) than those for the foodstuffs ingested on the survey day (0.75 and 0.81, respectively). Some exposure-related behaviors, namely the use of insecticides, herbicides, and insect repellent sprays, were found to be associated with increased Cr-unadjusted ΣDAP concentrations (odds ratio, 2.0-2.6) via multivariate analysis. In contrast, only the use of a fragrance or deodorant was associated with increased Cr-adjusted ΣDAP concentrations (odds ratio, 2.3). This is the first report on the exposure levels of OP pesticides in a large number of Japanese toddlers. Some household chemical product use was related to OP common metabolite DAP levels. Japanese toddlers were widely exposed to OP pesticide.