A cross-validation based approach for estimating specific gravity in elementary-school aged children using a nonlinear model

Environmental research often relies on urinary biomarkers which require dilution correction to accurately measure exposures. Specific gravity (SG) and creatinine (UCr) are commonly measured urinary dilution factors. Epidemiologic studies may assess only one of these measures, making it difficult to pool studies that may otherwise be able to be combined. Participants from the National Health and Nutrition Examination Survey 2007-2008 cycle were used to perform k-fold validation of a nonlinear model estimating SG from UCr. The final estimated model was applied to participants from the School Inner-City Asthma Intervention Study, who submitted urinary samples to the Children's Health Exposure Analysis Resource. Model performance was evaluated using calibration metrics to determine how closely the average estimated SG was to the measured SG. Additional models, with interaction terms for age, sex, body mass index, race/ethnicity, relative time of day when sample was collected, log transformed 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), and asthma status were estimated and assessed for improvement. The association between monobenzyl phthalate (MBZP) and asthma symptom days, controlling for measured UCr, measured SG, and each estimated SG were compared to assess validity of the estimated SG. The model estimating SG from UCr alone, resulted in a beta estimate of 1.10 (95% CI: 1.01, 1.19), indicating agreement between model-predicted SG and measured SG. Inclusion of age and sex in the model improved estimation (β = 1.06, 95% CI: 0.98, 1.15). The full model accounting for all interaction terms with UCr resulted in the best agreement (β = 1.01, 95% CI: 0.93,1.09). Associations between MBZP and asthma symptoms days, controlling for each estimated SG, were within the range of effect estimates when controlling for measured SG and measured UCr (Rate ratios = 1.28-1.34). Our nonlinear modeling provides opportunities to estimate SG in studies that measure UCr or vice versa, enabling data pooling despite differences in urine dilution factors.

Human Microbiome Mixture Analysis Using Weighted Quantile Sum Regression

Studies of the health effects of the microbiome often measure overall associations by using diversity metrics, and individual taxa associations in separate analyses, but do not consider the correlated relationships between taxa in the microbiome. In this study, we applied random subset weighted quantile sum regression with repeated holdouts (WQS_RSRH), a mixture method successfully applied to 'omic data to account for relationships between many predictors, to processed amplicon sequencing data from the Human Microbiome Project. We simulated a binary variable associated with 20 operational taxonomic units (OTUs). WQS_RSRH was used to test for the association between the microbiome and the simulated variable, adjusted for sex, and sensitivity and specificity were calculated. The WQS_RSRH method was also compared to other standard methods for microbiome analysis. The method was further illustrated using real data from the Growth and Obesity Cohort in Chile to assess the association between the gut microbiome and body mass index. In the analysis with simulated data, WQS_RSRH predicted the correct directionality of association between the microbiome and the simulated variable, with an average sensitivity and specificity of 75% and 70%, respectively, in identifying the 20 associated OTUs. WQS_RSRH performed better than all other comparison methods. In the illustration analysis of the gut microbiome and obesity, the WQS_RSRH analysis identified an inverse association between body mass index and the gut microbe mixture, identifying Bacteroides, Clostridium, Prevotella, and Ruminococcus as important genera in the negative association. The application of WQS_RSRH to the microbiome allows for analysis of the mixture effect of all the taxa in the microbiome, while simultaneously identifying the most important to the mixture, and allowing for covariate adjustment. It outperformed other methods when using simulated data, and in analysis with real data found results consistent with other study findings.

Application of growth modeling to assess the impact of hospital-based phthalate exposure on preterm infant growth parameters during the neonatal intensive care unit hospitalization

In this study, we use advanced growth modeling techniques and the rich biospecimen and data repositories of the NICU Hospital Exposures and Long-Term Health (NICU-HEALTH) study to assess the impact of NICU-based phthalate exposure on extrauterine growth trajectories between birth and NICU discharge. Repeated holdout weighed quantile sum (WQS) regression was used to assess the effect of phthalate mixtures on the latency to first growth spurt and on the rate of first growth spurt. Further, we assessed sex as an effect modifier of the relationship between a phthalate mixture and both outcomes. Nine phthalate metabolites, mono-ethyl phthalate (MEP), mono-benzyl phthalate (MBzP), mono-n-butyl phthalate (MBP), mono-isobutyl phthalate (MiBP), mono-(3-carboxypropyl) phthalate (MCPP), mono-2-ethylhexyl phthalate (MEHP), mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP) were measured in weekly urine specimens from 101 NICU-HEALTH participants between birth and the first growth spurt. Phthalate levels varied by species but not by infant sex, and decreased over the course of the NICU hospitalization as presented in detail in Stroustrup et al., 2018. There was evidence of nonlinearity when assessing the effect of phthalates on latency to first growth spurt. Above a threshold level, a higher phthalate mixture with dominant contributors MCPP, MBzP, and MEP predicted a shorter latency to the first inflection point, or an earlier growth spurt. A higher phthalate mixture with dominant contributors MECPP, MEHHP, and MEOHP was associated with an increased rate of growth. Results of both models were clearly different for boys and girls, consistent with other studies showing the sexually dimorphic impact of early life phthalate exposure. These results suggest that growth curve modeling facilitates evaluation of discrete periods of rapid growth during the NICU hospitalization and exposure to specific phthalates during the NICU hospitalization may both alter the timing of the first growth spurt and result in more rapid growth in a sexually dimorphic manner.

Prenatal Metal Exposures and Associations with Kidney Injury Biomarkers in Children

Prenatal exposure to arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb) may be nephrotoxic, yet limited studies have examined subclinical kidney injury biomarkers in children. We assessed whether metal exposure in the second trimester (2T), a crucial time of kidney development, is associated with altered urine kidney injury and function biomarkers in preadolescent children. Analyses included 494 children participating in a birth cohort study in Mexico City. Concentrations of As, Cd, and Pb were measured from pregnant women in 2T blood and urine, and Hg in urine only. Kidney biomarkers were measured from children in urine at age 8-12 years. We assessed the associations between individual metals and (1) kidney biomarkers using linear regression and (2) a multi-protein kidney mixture using weighted quantile sum (WQS) regression. Associations of separate urine and blood metal mixtures with individual kidney biomarkers were assessed via WQS. Within the multi-protein mixture, the association with increased urinary As was predominated by urine alpha-1-microglobulin (A1M), interferon gamma-induced protein 10 (IP10), and fatty acid binding protein 1; the association with increased urinary Cd was predominated by A1M, clusterin, and albumin. The urine metal mixture was associated with increased albumin (0.23 ng/mL; 95% confidence interval (CI): 0.10, 0.37), IP10 (0.15 ng/mL; 95% CI: 0.02, 0.28), and cystatin C (0.17 ng/mL; 95% CI: 0.04, 0.31); these associations were mainly driven by urinary As and Cd. We observed null associations between prenatal blood or urine metal mixtures and estimated glomerular filtration rate. Higher prenatal urinary metals, individually and as a mixture were associated with altered kidney injury biomarkers in children. Further research and longer participant follow-up are required to ascertain the risk of kidney disease later in life.

Individual Nutrition Is Associated with Altered Gut Microbiome Composition for Adults with Food Insecurity

Diet is widely recognized as a key contributor to human gut microbiome composition and function. However, overall nutrition can be difficult to compare across a population with varying diets. Moreover, the role of food security in the relationship with overall nutrition and the gut microbiome is unclear. This study aims to investigate the association between personalized nutrition scores, variation in the adult gut microbiome, and modification by food insecurity. The data originate from the Survey of the Health of Wisconsin and the Wisconsin Microbiome Study. Individual nutrition scores were assessed using My Nutrition Index (MNI), calculated using data from food frequency questionnaires, and additional health history and demographic surveys. Food security and covariate data were measured through self-reported questionnaires. The gut microbiome was assessed using 16S amplicon sequencing of DNA extracted from stool samples. Associations, adjusted for confounding and interaction by food security, were estimated using Weighted Quantile Sum (WQS) regression models with Random Subset and Repeated Holdout extensions (WQSRSRH), with bacterial taxa used as components in the weighted index. Of 643 participants, the average MNI was 66.5 (SD = 31.9), and 22.8% of participants were food insecure. Increased MNI was significantly associated with altered gut microbial composition (β = 2.56, 95% CI = 0.52−4.61), with Ruminococcus, Oscillospira, and Blautia among the most heavily weighted of the 21 genera associated with the MNI score. In the stratified interaction WQSRSRH models, the bacterial taxa most heavily weighted in the association with MNI differed by food security, but the level of association between MNI and the gut microbiome was not significantly different. More bacterial genera are important in the association with higher nutrition scores for people with food insecurity versus food security, including Streptococcus, Parabacteroides Faecalibacterium, and Desulfovibrio. Individual nutrition scores are associated with differences in adult gut microbiome composition. The bacterial taxa most associated with nutrition vary by level of food security. While further investigation is needed, results showed a higher nutrition score was associated with a wider range of bacterial taxa for food insecure vs. secure, suggesting nutritional quality in food insecure individuals is important in maintaining health and reducing disparities.

Prenatal and early childhood critical windows for the association of nephrotoxic metal and metalloid mixtures with kidney function

INTRODUCTION

As renal development and maturation processes begin in utero and continue through early childhood, sensitive developmental periods arise during which metal exposures can program subclinical nephrotoxicity that manifests later in life. We used novel dentine biomarkers of established nephrotoxicants including arsenic (As), cadmium (Cd), lead (Pb), chromium (Cr), and lithium (Li), and their mixtures, to identify critical windows of exposure-associated kidney function alterations in preadolescents.

METHODS

Participants included 353 children in the Programming Research in Obesity Growth, Environment and Social Stressors (PROGRESS) longitudinal birth cohort study based in Mexico City. Estimated glomerular filtration rate (eGFR) was assessed in 8-12 year old children using serum cystatin C measures. Pre- and postnatal metal(loid) concentrations were assessed in weekly increments by analyzing deciduous teeth with laser ablation-inductively coupled plasma-mass spectrometry. We used reverse distributed lag models (rDLMs) and lagged Weighted Quantile Sum (L-WQS) regression to examine time-varying associations between weekly perinatal metal(loid) exposure or metal(loid) mixtures and preadolescent eGFR while adjusting for age, sex, BMI z-score, SES and prenatal tobacco smoke exposure.

RESULTS

We identified a critical window of susceptibility to Pb exposure, in the late 3rd trimester (5 weeks prior to birth) during which higher Pb exposure was associated with children's increased eGFR. When all elements were assessed as a mixture, we identified late 2nd/early 3rd trimester (weeks 8-17 of gestation) as a window of vulnerability associated with decreased eGFR, with Li and Cr contributing the greatest weights to the association. When stratified by sex, we observed stronger effects among boys than girls.

CONCLUSIONS

Using tooth-matrix biomarkers, we identified discrete developmental exposure windows wherein Pb and metal(loid) mixtures were associated with altered preadolescent kidney function.

Association between prenatal metal exposure and adverse respiratory symptoms in childhood

INTRODUCTION

Manganese and lead have been cross-sectionally associated with adverse respiratory outcomes in childhood but there is limited data on their combined effects starting in utero. We examined associations between in utero exposure to metals and childhood respiratory symptoms.

METHODS

We assessed 633 mother-child dyads enrolled in the Programming Research in Obesity, Growth, Environment, and Social Stressors (PROGRESS) birth cohort in Mexico City. Blood manganese (BMn) and lead (BPb) were measured in mothers at 2^nd and 3^rd trimester. Ever wheeze, current wheeze and asthma diagnosis were ascertained at 4-5 and 6-7 year visits through the International Study of Asthma and Allergies in Childhood survey. Logistic mixed model regression was used to assess the association between prenatal metals and respiratory outcomes in children across the 4-5 and 6-7 year visits. Covariates included mother's age, education and asthma, environmental tobacco smoke, child's sex and assessment time.

RESULTS

In adjusted models, higher 2^nd trimester BPb had a significant association with elevated odds of ever wheeze (Odds Ratio (OR): 1.97, 95% CI: 1.05, 3.67). BMn at 2nd trimester was associated with decreased (OR: 0.06, 95% CI: 0.01, 0.35) odds of current wheeze. We did not find any statistically significant associations with 3rd trimester blood metals.

CONCLUSION

Prenatal exposure to Pb was associated with higher odds of ever wheeze while Mn was negatively associated with odds of current wheeze. These findings underscore the need to consider prenatal metal exposure, including low exposure levels, in the study of adverse respiratory outcomes.

Environmental exposures to pesticides, phthalates, phenols and trace elements are associated with neurodevelopment in the CHARGE study

OBJECTIVE

To determine if higher exposures measured in early childhood to environmental phenols, phthalates, pesticides, and/or trace elements, are associated with increased odds of having a diagnosis of Autism Spectrum Disorder (ASD), Developmental Delay (DD), or Other Early Concerns (OEC) compared to typically developing children (TD).

METHODS

This study included 627 children between the ages of 2-5 who participated in the Childhood Autism Risks from Genetics and Environment (CHARGE) study. Urine samples were collected at the same study visit where diagnostic assessments to confirm diagnosis indicated during the recruitment process were performed. Adjusted multinomial regression models of each chemical with diagnosis as the outcome were conducted. Additionally, two methods were used to analyze mixtures: repeated holdout multinomial weighted quantile sum (WQS) regression for each chemical class; and a total urinary mixture effect was assessed with repeated holdout random subset WQS.

RESULTS

Many urinary chemicals were associated with increased odds of ASD, DD or OEC compared to TD; however, most did not remain significant after false discovery rate adjustment. Repeated holdout WQS indices provided evidence for associations of both a phenol/paraben mixture effect and a trace element mixture effect on DD independently. In analyses adjusted for confounders and other exposures, results suggested an association of a pesticide mixture effect with increased risk for ASD. Results also suggested associations of a total urinary mixture with greater odds of both ASD and DD separately.

CONCLUSION

Higher concentrations of urinary biomarkers were associated with ASD, DD, and OEC compared to TD, with consistency of the results comparing single chemical analyses and mixture analyses. Given that the biospecimens used for chemical analysis were generally collected many months after diagnoses were made, the direction of any causal association is unknown. Hence findings may reflect higher exposures among children with non-typical development than TD children due to differences in behaviors, metabolism, or toxicokinetics.

My nutrition index: a method for measuring optimal daily nutrient intake

Background

Adequate nutrition is essential for individual and population level health. However, determining adequacy of daily nutrient intake in research studies is often challenging given the unique nutritional needs of individuals. Herein, we examine construct, predictive, criterion, content, and concurrent validity of a dietary analytic tool – My Nutrition Index (MNI) for measuring nutrient intake in relation to personalized daily nutrient intake guidelines. MNI gauges adequacy of an individual’s daily nutrient intake based on his or her unique demographic and lifestyle characteristics. MNI accounts for potential adverse effects of inadequate and excess nutrient consumption.

Methods

MNI, calculated based on 34 nutrients, provides an overall index score ranging from 0 to 100, with higher scores reflecting a more nutritious diet. We calculated MNI scores for 7154 participants ages 18-65 in the National Health and Nutrition Examination Surveys (2007-2014) by using average nutrient intakes from two 24-h dietary recalls. Survey-weighted binary logistic regression models were used to assess associations between MNI scores and obesity, depression, health perceptions, and past or present cardiovascular disease.

Results

Higher MNI scores were associated with lower prevalence of self-reported cardiovascular disease (OR = 0.69, CI: 0.52, 0.92, p = 0.012), depression (OR = 0.76, CI: 0.65, 0.90, p < 0.001), and obesity (OR = 0.92, CI: 0.87, 0.99, p = 0.016), as well as more favorable health perceptions (OR = 1.24, CI: 1.13, 1.37, p < 0.001).

Conclusions

MNI provides an individualized approach for measuring adequacy/sufficiency of daily nutrient intake that can validly be employed to assess relationships between nutrition and health outcomes in research studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40795-022-00497-9.

A Mixture of Endocrine Disrupting Chemicals Associated with Lower Birth Weight in Children Induces Adipogenesis and DNA Methylation Changes in Human Mesenchymal Stem Cells

Endocrine Disrupting Chemicals (EDCs) are man-made compounds that alter functions of the endocrine system. Environmental mixtures of EDCs might have adverse effects on human health, even though their individual concentrations are below regulatory levels of concerns. However, studies identifying and experimentally testing adverse effects of real-life mixtures are scarce. In this study, we aimed at evaluating an epidemiologically identified EDC mixture in an experimental setting to delineate its cellular and epigenetic effects. The mixture was established using data from the Swedish Environmental Longitudinal Mother and child Asthma and allergy (SELMA) study where it was associated with lower birth weight, an early marker for prenatal metabolic programming. This mixture was then tested for its ability to change metabolic programming of human mesenchymal stem cells. In these cells, we assessed if the mixture induced adipogenesis and genome-wide DNA methylation changes. The mixture increased lipid droplet accumulation already at concentrations corresponding to levels measured in the pregnant women of the SELMA study. Furthermore, we identified differentially methylated regions in genes important for adipogenesis and thermogenesis. This study shows that a mixture reflecting human real-life exposure can induce molecular and cellular changes during development that could underlie adverse outcomes.

From cohorts to molecules: Adverse impacts of endocrine disrupting mixtures

Convergent evidence associates exposure to endocrine disrupting chemicals (EDCs) with major human diseases, even at regulation-compliant concentrations. This might be because humans are exposed to EDC mixtures, whereas chemical regulation is based on a risk assessment of individual compounds. Here, we developed a mixture-centered risk assessment strategy that integrates epidemiological and experimental evidence. We identified that exposure to an EDC mixture in early pregnancy is associated with language delay in offspring. At human-relevant concentrations, this mixture disrupted hormone-regulated and disease-relevant regulatory networks in human brain organoids and in the model organisms Xenopus leavis and Danio rerio, as well as behavioral responses. Reinterrogating epidemiological data, we found that up to 54% of the children had prenatal exposures above experimentally derived levels of concern, reaching, for the upper decile compared with the lowest decile of exposure, a 3.3 times higher risk of language delay.

Using Metrics of a Mixture Effect and Nutrition from an Observational Study for Consideration towards Causal Inference

Environmental exposures to a myriad of chemicals are associated with adverse health effects in humans, while good nutrition is associated with improved health. Single chemical in vivo and in vitro studies demonstrate causal links between the chemicals and outcomes, but such studies do not represent human exposure to environmental mixtures. One way of summarizing the effect of the joint action of chemical mixtures is through an empirically weighted index using weighted quantile sum (WQS) regression. My Nutrition Index (MNI) is a metric of overall dietary nutrition based on guideline values, including for pregnant women. Our objective is to demonstrate the use of an index as a metric for more causally linking human exposure to health outcomes using observational data. We use both a WQS index of 26 endocrine-disrupting chemicals (EDCs) and MNI using data from the SELMA pregnancy cohort to conduct causal inference using g-computation with counterfactuals for assumed either reduced prenatal EDC exposures or improved prenatal nutrition. Reducing the EDC exposure using the WQS index as a metric or improving dietary nutrition using MNI as a metric, the counterfactuals in a causal inference with one SD change indicate significant improvement in cognitive function. Evaluation of such a strategy may support decision makers for risk management of EDCs and individual choices for improving dietary nutrition.

Powering Research through Innovative Methods for Mixtures in Epidemiology (PRIME) Program: Novel and Expanded Statistical Methods

Humans are exposed to a diverse mixture of chemical and non-chemical exposures across their lifetimes. Well-designed epidemiology studies as well as sophisticated exposure science and related technologies enable the investigation of the health impacts of mixtures. While existing statistical methods can address the most basic questions related to the association between environmental mixtures and health endpoints, there were gaps in our ability to learn from mixtures data in several common epidemiologic scenarios, including high correlation among health and exposure measures in space and/or time, the presence of missing observations, the violation of important modeling assumptions, and the presence of computational challenges incurred by current implementations. To address these and other challenges, NIEHS initiated the Powering Research through Innovative methods for Mixtures in Epidemiology (PRIME) program, to support work on the development and expansion of statistical methods for mixtures. Six independent projects supported by PRIME have been highly productive but their methods have not yet been described collectively in a way that would inform application. We review 37 new methods from PRIME projects and summarize the work across previously published research questions, to inform methods selection and increase awareness of these new methods. We highlight important statistical advancements considering data science strategies, exposure-response estimation, timing of exposures, epidemiological methods, the incorporation of toxicity/chemical information, spatiotemporal data, risk assessment, and model performance, efficiency, and interpretation. Importantly, we link to software to encourage application and testing on other datasets. This review can enable more informed analyses of environmental mixtures. We stress training for early career scientists as well as innovation in statistical methodology as an ongoing need. Ultimately, we direct efforts to the common goal of reducing harmful exposures to improve public health.

Prenatal metal mixture concentrations and reward motivation in children

Reward motivation is a complex umbrella term encompassing the cognitions, emotions, and behaviors involved in the activation, execution, and persistence of goal-directed behavior. Altered reward motivation in children is characteristic of many neurodevelopmental and psychiatric disorders. Previously difficult to operationalize, the Progressive Ratio (PR) task has been widely used to assess reward motivation in animal and human studies, including children. Because the neural circuitry supporting reward motivation starts developing during pregnancy, and is sensitive to disruption by environmental toxicants, including metals, the goal of this study was to examine the association between prenatal concentrations of a mixture of neurotoxic metals and reward motivation in children. We measured reward motivation by administering a PR test to 373 children ages 6-8 years enrolled in the Programming Research in Obesity, Growth, Environment and Social Stressors (PROGRESS) Study in Mexico City. Children were asked to press a response lever for a token reward; one press on the response lever was required to earn the first token and each subsequent token required an additional 10 lever presses. Maternal blood concentrations of lead, manganese, zinc, arsenic, cadmium, and selenium were measured using inductively-coupled plasma mass spectrometry during the 2nd and 3rd trimesters of pregnancy. We performed generalized Weighted Quantile Sum (gWQS) regression analyses to examine associations between the prenatal metal mixture and reward motivation; adjusting for child sex, birthweight and age; and maternal IQ, education, and socioeconomic status. The prenatal metal mixture was significantly associated with higher motivation as indicated by more lever presses (ß = 0.02, p < 0.001) and a shorter time between receiving the reinforcer and the first press (ß = 0.23, p = 0.01), and between subsequent presses (ß = 0.07, p = 0.005). Contributions of different metals to this association differed by trimester and child sex. These findings suggest that children with increased exposure to metal during the 2nd and 3rd trimesters of gestation demonstrate increased reward motivation, which may reflect a tendency to perseverate or hypersensitivity to positive reinforcement.

Prenatal blood lead levels and reduced preadolescent glomerular filtration rate: Modification by body mass index

BACKGROUND

For the developing kidney, the prenatal period may represent a critical window of vulnerability to environmental insults resulting in permanent nephron loss. Given that the majority of nephron formation is complete in the 3rd trimester, we set out to test whether 1) prenatal lead exposure is associated with decreased preadolescent kidney function and 2) whether preadolescent obesity acts synergistically with early life lead exposure to reduce kidney function.

METHODS

Our study included 453 mother-child pairs participating in the PROGRESS birth cohort. We assessed prenatal blood lead levels (BLLs) in samples collected in the 2nd and 3rd trimesters and at delivery, as well as tibial and patellar bone lead measures assessed one-month postpartum. Preadolescent estimated glomerular filtration rate (eGFR) was derived from serum levels of creatinine and/or cystatin C measured at age 8-12 years. We applied linear regression to assess the relationship between prenatal bone and BLL with preadolescent eGFR, and adjusted for covariates including age, sex, BMI z-score, indoor tobacco smoke exposure, and socioeconomic status. We also examined sex-specific associations and tested for effect modification by BMI status.

RESULTS

We observed null associations between prenatal lead exposure and eGFR. However, in interaction analyses we found that among overweight children, there was an inverse association between BLL (assessed at 2nd and 3rd trimester and at delivery) and preadolescent eGFR. For example, among overweight participants, a one ln-unit increase in 2nd trimester BLL was associated with a 10.5 unit decrease in cystatin C-based eGFR (95% CI: -18.1, -2.8; p = 0.008). Regardless of lead exposure, we also observed null relationships between BMI z-score and eGFR overall, as well as among overweight participants. However, among participants with preadolescent obesity, we observed a significant 5.9-unit decrease in eGFR. We observed no evidence of sex-specific effects.

CONCLUSIONS

Our findings, if confirmed in other studies, suggest a complex interplay between the combined adverse effects of adiposity and perinatal lead exposure as they relate to adolescent kidney function. Future studies will assess kidney function and adiposity trajectories through adolescence to better understand environmental risk factors for kidney function decline.

Prenatal exposures to mixtures of endocrine disrupting chemicals and children's weight trajectory up to age 5.5 in the SELMA study

Exposure to endocrine disrupting chemicals (EDCs) may impact early growth, although information is limited on exposure to combination of multiple EDCs. We aimed to evaluate the effect of prenatal exposure to EDC mixtures on birthweight z-scores and childhood weight trajectories. Twenty-six proven and suspected EDCs, were analyzed in prenatal urine and blood samples from 1118 mothers participating in the Swedish Environmental Longitudinal Mother and child Asthma and allergy (SELMA) study. Two growth parameters were estimated from each child's weight trajectory from birth to 5.5 years of age: infant growth spurt rate and age at infant peak growth velocity (PGV). Weighted quantile sum (WQS) regression was used to estimate the mixture effect and identify chemicals of concern. A one-unit increase in the EDC mixture WQS index, was associated with decreased birthweight z-scores of 0.11 (95% CI - 0.16, - 0.06), slower infant growth spurt rate of 0.01 (95% CI - 0.03, - 0.01, on the log10 scale), and delayed age at infant PGV of 0.15 months (95% CI 0.07, 0.24) after adjusting for potential confounders. Stratified analysis by sex, showed that delayed age at infant PGV was mostly observed in girls with 0.51 months (95% CI 0.26, 0.76). Identified chemicals of concern included perfluorinated alkyl substances (PFAS), Triclosan, phthalates, non-phthalate plasticizers, bisphenols, polycyclic aromatic hydrocarbons, pesticides and PCBs. Prenatal exposure to EDC mixtures was associated with lower birthweight and altered infant weight gain trajectories.

Reflection on modern methods: good practices for applied statistical learning in epidemiology

Statistical learning includes methods that extract knowledge from complex data. Statistical learning methods beyond generalized linear models, such as shrinkage methods or kernel smoothing methods, are being increasingly implemented in public health research and epidemiology because they can perform better in instances with complex or high-dimensional data-settings in which traditional statistical methods fail. These novel methods, however, often include random sampling which may induce variability in results. Best practices in data science can help to ensure robustness. As a case study, we included four statistical learning models that have been applied previously to analyze the relationship between environmental mixtures and health outcomes. We ran each model across 100 initializing values for random number generation, or 'seeds', and assessed variability in resulting estimation and inference. All methods exhibited some seed-dependent variability in results. The degree of variability differed across methods and exposure of interest. Any statistical learning method reliant on a random seed will exhibit some degree of seed sensitivity. We recommend that researchers repeat their analysis with various seeds as a sensitivity analysis when implementing these methods to enhance interpretability and robustness of results.

Prenatal exposure to bisphenols and cognitive function in children at 7 years of age in the Swedish SELMA study

BACKGROUND

Experimental evidence demonstrates that exposure to bisphenol A (BPA), and the recently introduced alternatives bisphenol S (BPS) and bisphenol F (BPF) alter normal neurodevelopment. More research is needed to evaluate the associations between exposure to individual BPA alternatives and neurodevelopmental outcomes in humans.

OBJECTIVE

The present study aimed at examining the individual associations between prenatal BPA, BPS and BPF exposure and cognitive outcomes in children at age 7 years.

METHOD

Women were enrolled in the Swedish Environmental Longitudinal Mother and Child, Asthma and Allergy (SELMA) study, at gestational median week 10.0, and their children were examined for cognitive function at 7 years of age (N = 803). Maternal urinary BPA, BPS, and BPF concentrations were measured at enrollment and childreńs cognitive function at the age of 7 years was measured using the Wechsler Intelligence Scale for Children IV (WISC-IV).

RESULTS

All three bisphenols were detected in over 90% of the women, where BPA had the highest geometric mean concentrations (1.55 ng/mL), followed by BPF (0.16 ng/mL) and BPS (0.07 ng/mL). Prenatal BPF exposure was associated with decreased full scale IQ (β = -1.96, 95%CI; -3.12; -0.80), as well as with a decrease in all four sub scales covering verbal comprehension, perceptual reasoning, working memory and processing speed. This association corresponded to a 1.6-point lower IQ score for an inter-quartile-range (IQR) change in prenatal BPF exposure (IQR = 0.054-0.350 ng/mL). In sex-stratified analyses, significant associations with full scale IQ were found for boys (β = -2.86, 95%CI; -4.54; -1.18), while the associations for girls did not reach significance (β = -1.38, 95%CI; -2.97; 0.22). No significant associations between BPA nor BPS and cognition were found.

DISCUSSION

Prenatal exposure to BPF was significantly associated with childreńs cognitive function at 7 years. Since BPF is replacing BPA in numerous consumer products globally, this finding urgently call for further studies.

Evaluating inter-study variability in phthalate and trace element analyses within the Children's Health Exposure Analysis Resource (CHEAR) using multivariate control charts

BACKGROUND

The Children's Health Exposure Analysis Resource (CHEAR) program allows researchers to expand their research goals by offering the assessment of environmental exposures in their previously collected biospecimens. Samples are analyzed in one of CHEAR's network of six laboratory hubs with the ability to assess a wide array of environmental chemicals. The ability to assess inter-study variability is important for researchers who want to combine datasets across studies and laboratories.

OBJECTIVE

Herein we establish a process of evaluating inter-study variability for a given analytic method.

METHODS

Common quality control (QC) pools at two concentration levels (A and B) in urine were created within CHEAR for insertion into each batch of samples tested at a rate of three samples of each pool per 100 study samples. We assessed these QC pool results for seven phthalates analyzed for five CHEAR studies by three different lab hubs utilizing multivariate control charts to identify out-of-control runs or sets of samples associated with a given QC sample. We then tested the conditions that would lead to an out-of-control run by simulating outliers in an otherwise "in-control" set of 12 trace elements in blood QC samples (NIST SRM 955c).

RESULTS

When phthalates were assessed within study, we identified a single out-of-control run for two of the five studies. Combining QC results across lab hubs, all of the runs from these two studies were now in-control, while multiple runs from two other studies were pushed out-of-control. In our simulation study we found that 3-6 analytes with outlier values (5xSD) within a run would push that run out of control in 65-83% of simulations, respectively.

SIGNIFICANCE

We show how acceptable bounds of variability can be established for a given analytic method by evaluating QC materials across studies using multivariate control charts.

Exosomal miRNAs in urine associated with children's cardiorenal parameters: a cross-sectional study

Aims:

The authors sought to examine associations between urinary exosomal miRNAs (exo-miRs), emerging biomarkers of renal health, and cardiorenal outcomes in early childhood.

Materials & methods:

The authors extracted exo-miRs in urine from 88 healthy Mexican children aged 4–6 years. The authors measured associations between 193 exo-miRs and cardiorenal outcomes: systolic/diastolic blood pressure, estimated glomerular filtration rate and urinary sodium and potassium levels. The authors adjusted for age, sex, BMI, socioeconomic status, indoor tobacco smoke exposure and urine specific gravity.

Results:

Multiple exo-miRs were identified meeting a false discovery rate threshold of q < 0.1. Specifically, three exo-miRs had increased expression with urinary sodium, 17 with urinary sodium-to-potassium ratio and one with decreased estimated glomerular filtration rate.

Conclusions:

These results highlight urinary exo-miRs as early-life biomarkers of children's cardiorenal health.

Integrated measures of lead and manganese exposure improve estimation of their joint effects on cognition in Italian school-age children

Every day humans are exposed to mixtures of chemicals, such as lead (Pb) and manganese (Mn). An underappreciated aspect of studying the health effects of mixtures is the role that the exposure biomarker media (blood, hair, etc.) may play in estimating the effects of the mixture. Different biomarker media represent different aspects of each chemical's toxicokinetics, thus no single medium can fully capture the toxicokinetic profile for all the chemicals in a mixture. A potential solution to this problem is to combine exposure data across different media to derive integrated estimates of each chemical's internal concentration. This concept, formalized as a multi-media biomarker (MMB) has proven effective for estimating the health impacts of Pb exposure, but may also be useful to estimate mixture effects, such as the joint effects of metals like Pb and Mn, while factoring in how the association changes based upon the biomarker media. Levels of Pb and Mn were quantified in five media: blood, hair, nails, urine, and saliva in the Public Health Impact of Metals Exposure (PHIME) project, a study of Italian adolescents aged 10-14 years. MMBs were derived for both metals using weighted quantile sum (WQS) regression across the five media. Age-adjusted Wechsler Intelligence Scale for Children (WISC) IQ scores, measured at the same time as the exposure measures, were the primary outcome and models were adjusted for sex and socioeconomic status. The levels Pb and Mn were relatively low, with median blood Pb of 1.27 (IQR: 0.84) μg/dL and median blood Mn of 1.09 (IQR: 0.45) μg/dL. Quartile increases in a Pb-Mn combination predicted decreased Full Scale IQ of 1.9 points (95% CI: 0.3, 3.5) when Pb and Mn exposure levels were estimated using MMBs, while individual regressions for each metal were not associated with Full Scale IQ. Additionally, a quartile increase in the WQS index of Pb and Mn, measured using MMBs, were associated with reductions in Verbal IQ by 2.8 points (1.0, 4.5). Weights that determine the contributions of the metals to the joint effect highlighted that the contribution of the Pb-Mn was 72-28% for Full Scale IQ and 42-58% for Verbal IQ. We found that the joint effects of Pb and Mn are strongly affected by the medium used to measure exposure and that the joint effects of the Pb and Mn MMBs on cognition were the stronger than any individual biomarker. Thus, increase power and accuracy for measuring mixture effects compared to individual biomarkers. As the number of chemicals in mixtures increases, appropriate biomarker selection will become increasingly important and MMBs are a natural way to reduce bias in such analyses.

Exposure to environmental chemical mixtures is associated with nasal colonization by Staphylococcus aureus: NHANES 2001-2004

BACKGROUND

Understanding the health effects of exposure to chemical mixtures is critically important given the broad range of concurrent exposures throughout the life-course. While investigations of environmental chemicals and components of the human microbiome are becoming more common, few have examined associations with chemical mixtures. This study assesses the association between exposure to mixtures of 66 different environmental chemicals and nasal colonization of Staphylococcus aureus (SA) and methicillin resistant SA (MRSA).

METHODS

Data came from the National Health and Nutrition Examination Survey (NHANES) 2001-2004. The analytical sample consists of 10,312 participants, age 6 years and older, subdivided into 8 groups with different chemical exposure mixtures. Within each of 6 chemical classes (metals, phthalates, polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs), polyfluorochemicals (PFCs), and phenols), weighted quantile sum (WQS) regression was used to analyze the joint association of the component compounds and nasal SA colonization. WQS was also used to assess the joint association of 3 chemical mixtures (metals, metal and PAHs, and metal and triclosan) and nasal MRSA colonization. All regression models were adjusted for confounders.

RESULTS

The analytical sample was between ages 6-85, slightly more female, and predominantly non-smokers. Prevalence of SA carriage was 29.2%, and MRSA colonization prevalence was 1.2%. Within each chemical class, odds of SA colonization increased statistically significantly with exposure to mixtures of metals (OR = 1.11, 95% CI = 1.02-1.20), phthalates (OR = 1.09, 95% CI = 1.04-1.14), and phenols (OR = 1.08, 95% CI = 1.01-1.15). Exposure to a mixture of metals combined with PAHs was also associated with increased odds of MRSA carriage (OR = 1.38, 95% CI = 1.02-1.86).

CONCLUSION

Results indicate an association between multiple environmental chemical mixtures and SA colonization, including MRSA. These findings support the need for further analysis of associations between chemical mixtures and SA colonization, as well as other components of the human microbiome.

Prenatal toxic metal mixture exposure and newborn telomere length: Modification by maternal antioxidant intake

BACKGROUND

Telomere length (TL) predicts the onset of cellular senescence and correlates with longevity and age-related disease risk. While telomeres erode throughout life, adults display fixed ranking and tracking of TL, supporting the importance of the early environment in determining inter-individual variability across the life course. Given their guanine-rich structure, telomeres are highly susceptible to oxidative stress (OS). We examined maternal metal exposure, which can induce OS, in relation to newborn TL. We also considered the modifying role of maternal antioxidant intake.

METHODS

Analyses included 100 mother-newborn pairs enrolled in the Boston and New York City-based PRogramming of Intergenerational Stress Mechanisms (PRISM) pregnancy cohort. We measured As, Ba, Cd, Ni, and Pb in maternal late-pregnancy urine by ICP-MS and quantified relative leukocyte TL (rLTL) in cord blood using qPCR. We used Weighted Quantile Sum (WQS) regression to estimate the metal mixture - rLTL association and conducted repeated holdout validation to improve the stability of estimates across data partitions. We examined models stratified by high (>median) versus low (≤median) maternal antioxidant intake, estimated from Block98 Food Frequency Questionnaires. We considered urinary creatinine, week of urine collection, maternal age, and race/ethnicity as covariates.

RESULTS

In adjusted models, urinary metals were inversely associated with newborn rLTL (βWQS = -0.50, 95% CI: -0.78, -0.21). The top metals contributing to the negative association included Ba (weight: 35.4%), Cd (24.5%) and Pb (26.9%). In models stratified by antioxidant intake, the significant inverse association between metals and rLTL remained only among mothers with low antioxidant intake (low: βWQS = -0.92, 95% CI: -1.53, -0.30; high: βWQS = -0.03, 95% CI: -0.58, 0.52). Results were similar in unadjusted models.

CONCLUSIONS

Relative LTL was shorter among newborns of mothers with higher exposure to metals during pregnancy. Higher maternal antioxidant intake may mitigate the negative influence of metals on newborn rLTL.

Contrasting prenatal nutrition and environmental exposures in association with birth weight and cognitive function in children at 7 years

Background

Good nutrition is essential for individual health, a notion that is particularly true during pregnancy. We have used a nutrition index that measures the adequacy of one’s diet relative to the unique nutritional needs of individuals due to, for example, their activity level, dietary restrictions, lifestyle and body size. The use of this personalised metric of dietary nutritiousness in the analysis of prenatal environmental exposures and developmental outcomes permits testing for potential mitigating effects of good nutrition. We also provide an analysis strategy for investigating the balance in beneficial food sources which are also the source of environmental toxicants.

Methods

A holistic measure of nutrition, My Nutrition Index (MNI), measures the nutrient quality (ie, ‘nutritiousness’) of a specified daily diet. MNI is calculated based on quantification of dozens of macronutrients and micronutrients that are specific to an individual’s nutritional needs by incorporating dietary restrictions, subject characteristics, activity level and health behaviours. The Swedish Environmental, Longitudinal, Mother and child, Asthma and allergy Study is a Swedish pregnancy cohort, with prenatal endocrine disrupting chemicals (EDCs) exposure and dietary data available. This makes it possible to test for the potential mitigating effects of good nutrition on health and development effects in offspring from EDCs.

Results

Using prenatal Food Frequency Questionnaire data to construct an individual’s MNI, the index was significantly and positively associated with important metabolic outcome (as measured by birth weight) and cognitive function at age 7 years (as measured by WISC IQ) in children when adjusted for covariates and prenatal concentrations of an EDC. In a stratified analysis of ‘low’ and ‘high’ fish consumption, a potential source of perfluoro-octanesulfonic acid (PFOS), the association between PFOS and birth weight was diminished in the high consumption group compared with the low consumption group.

Conclusions

Thus, MNI is evidently a metric of the general nutritiousness of daily diets and is useful in environmental health studies in representing the impact of good nutrition, even during pregnancy.