Lagged WQS regression for mixtures with many components

Associations between prenatal metal and metalloid mixtures in teeth and reductions in childhood lung function

BACKGROUND

Metal(oid)s have been cross-sectionally associated with lung function outcomes in childhood but there is limited data on their combined effects starting in utero. Child sex may further modify these effects.

OBJECTIVE

Examine associations between in utero and early life exposure to metals assessed via novel dentine biomarkers and childhood lung function and explore effect modification by child sex.

METHODS

Analyses included 291 children enrolled in the Programming Research in Obesity, Growth, Environment and Social Stressors (PROGRESS) study, a longitudinal birth cohort study in Mexico City. Weekly dentine levels of arsenic (As), cadmium (Cd), cobalt (Co), copper (Cu), manganese (Mn), nickel (Ni), and lead (Pb) were measured from 15 weeks pre-birth to 15 weeks post birth in deciduous children's teeth. Lung function was tested at ages 8-14 years and then modeled as age, height and sex adjusted z-scores. Associations were modeled using lagged weighted quantile sum (LWQS) regression to evaluate the potential for a time-varying mixture effect adjusting for maternal age and education at enrollment and exposure to environmental tobacco smoke in pregnancy. Models were also stratified by sex.

RESULTS

We identified a window of susceptibility at 12-15 weeks pre-birth in which the metal mixture was associated with lower FVC z-scores in children aged 8-14 years. Cd and Mn were the largest contributors to the mixture effect (70 %). There was also some evidence of effect modification by sex, in which the mean weights and weighted correlations over the identified window was more evident in males when compared to females. In the male stratum, Cd, Mn and additionally Pb also dominated the mixture association.

CONCLUSIONS

Prenatal metal(oid) exposure was associated with lower lung function in childhood. These findings underscore the need to consider both mixtures and windows of susceptibility to fully elucidate effects of prenatal metal(oid) exposure on childhood lung function.

A review of common statistical methods for dealing with multiple pollutant mixtures and multiple exposures

Traditional environmental epidemiology has consistently focused on studying the impact of single exposures on specific health outcomes, considering concurrent exposures as variables to be controlled. However, with the continuous changes in environment, humans are increasingly facing more complex exposures to multi-pollutant mixtures. In this context, accurately assessing the impact of multi-pollutant mixtures on health has become a central concern in current environmental research. Simultaneously, the continuous development and optimization of statistical methods offer robust support for handling large datasets, strengthening the capability to conduct in-depth research on the effects of multiple exposures on health. In order to examine complicated exposure mixtures, we introduce commonly used statistical methods and their developments, such as weighted quantile sum, bayesian kernel machine regression, toxic equivalency analysis, and others. Delineating their applications, advantages, weaknesses, and interpretability of results. It also provides guidance for researchers involved in studying multi-pollutant mixtures, aiding them in selecting appropriate statistical methods and utilizing R software for more accurate and comprehensive assessments of the impact of multi-pollutant mixtures on human health.

Single and mixed effects of multiple volatile organic compounds exposure on hematological parameters in the U.S. adult population

BACKGROUND

Most research exploring the correlation between volatile organic compounds (VOCs) and hematological parameters have focused on single VOCs. Our study aimed to explore the single and combined effects of VOCs on hematological parameters through three statistical models.

METHODS

Data from 4 cycles of the National Health and Nutrition Examination Survey (NHANES) were used in this study. The correlations between single exposure to 16 VOCs and hematological parameters in the general population were assessed by weighted multiple linear regression. Weighted quantile sum (WQS) and Bayesian kernel machine regression (BKMR) models were used to explore the relationship between the combined important VOCs selected by the least absolute shrinkage and selection operator (LASSO) and hematological parameters, as well as the effects of smoking status on them.

RESULTS

A total of 4089 adults were included in the study. We found that a variety of VOCs were significantly associated with hematological parameters. Among them, N-acetyl-S-(benzyl)-l-cysteine (BMA) was significantly negatively correlated with white blood cell (WBC), red blood cell (RBC), lymphocyte, and neutrophil counts. N-acetyl-S-(3-hydroxypropyl-1-methyl)-l-cysteine (HPMMA) was significantly positively correlated with WBC, monocyte, lymphocyte, and neutrophil counts. In the WQS analysis, the WQS index of the VOCs mixtures was positively correlated with WBC (β: 0.031; P < 0.001), monocyte (0.023; P = 0.021), and neutrophil (0.040; P = 0.001) counts, while negatively associated with RBC (-0.013; P < 0.001) counts. The BKMR model revealed that combined exposure to VOCs levels ≥70th percentile was significantly associated with lower RBC counts, and BMA was identified as the dominant contributor. Smoking significantly influenced the relationship between VOCs and hematological parameters.

CONCLUSIONS

Our study indicated the effects of single and overall VOCs exposure on hematological parameters and suggested the hematotoxicity as well as pro-inflammatory effects of VOCs, which had strong public health implications for reducing the potential health hazards of VOCs exposure to the hematologic system.

Cholesterol mediates the effects of single and multiple environmental phenols in urine on obesity

BACKGROUND

Overweight and obesity are among the leading chronic diseases worldwide. Environmental phenols have been renowned as endocrine disruptors that contribute to weight changes; however, the effects of exposure to mixed phenols on obesity are not well established.

METHODS

Using data from adults in National Health and Nutrition Examination Survey, this study examined the individual and combined effects of four phenols on obesity. A combination of traditional logistic regression and two mixed models (weighted quantile sum (WQS) regression and Bayesian kernel-machine regression (BKMR)) were used together to assess the role of phenols in the development of obesity. The potential mediation of cholesterol on these effects was analyzed through a parallel mediation model.

RESULTS

The results demonstrated that solitary phenols except triclosan were inversely associated with obesity (P-value < 0.05). The WQS index was also negatively correlated with general obesity (β: 0.770, 95% CI: 0.644-0.919, P-value = 0.004) and abdominal obesity (β: 0.781, 95% CI: 0.658-0.928, P-value = 0.004). Consistently, the BKMR model demonstrated the significant joint negative effects of phenols on obesity. The parallel mediation analysis revealed that high-density lipoprotein mediated the effects of all four single phenols on obesity, whereas low-density lipoprotein only mediated the association between benzophenol-3 and obesity. Moreover, Cholesterol acts as a mediator of the association between mixed phenols and obesity. Exposure to single and mixed phenols significantly and negatively correlated with obesity. Cholesterol mediated the association of single and mixed environmental phenols with obesity.

CONCLUSIONS

Assessing the potential public health risks of mixed phenols helps to incorporate this information into practical health advice and guidance.

Exposure to per- and polyfluoroalkyl substance and metabolic syndrome: A nationally representative cross-sectional study from NHANES, 2003-2018

Per- and polyfluoroalkyl substances(PFAS) are widespread organic pollutants with endocrine-disrupting effects on human health, but the association of PFAS exposure with metabolic syndrome remains conflicting. National Health and Nutrition Examination Survey(NHANES) program was utilized to evaluate the association of individual PFAS exposure and metabolic disorders and further determined the joint effect of PFAS co-exposures. 13921 participants and five PFAS exposures(PFHxS, MPAH, PFDE, PFNA, and PFUA) were included for analysis. The association between individual PFAS and metabolic syndrome varied in the specific PFAS and the specific metabolic disorder examined. PFHxS was negatively associated with obesity(Q4; OR = 0.75; P < 0.001), but positively associated with hyperlipidemia (Q3; OR = 1.2; P = 0.013). PFUA was negatively associated with obesity (Q4; OR = 0.6; P < 0.001), hyperlipidemia (Q3; OR = 0.85; P = 0.03), and non-alcoholic fatty liver disease (NAFLD, Q4; OR = 0.64; P = 0.015), but positively associated with hyperglycemia(Q3; OR = 1.27; P = 0.004). Furthermore, PFAS co-exposures were negatively associated with obesity(OR = 0.63; P < 0.001) and NAFLD(OR = 0.85; P = 0.021), and positively associated with hyperlipidemia(OR = 1.05; P = 0.022), but not significantly associated with hyperglycemia or hypertension. Overall, there was a negative association between PFAS co-exposures and metabolic severity score(β = -0.15; P < 0.001). Subgroup analysis stratified by gender and obesity consistently showed the negative association of PFAS co-exposures with metabolic severity score, and the positive association with hyperlipidemia. However, subgroup analysis showed a negative association with NAFLD in females but not in males, and a negative association with hyperglycemia in the obesity group, but not in the non-obesity group. Collectively, our study showed a negative association of PFAS co-exposures with metabolic syndrome severity score, but did not support a consistent association between PFAS co-exposures and individual components of metabolic syndrome. Additionally, there were gender-specific as well as BMI-specific differences in these associations. Further studies are needed to rule out the reverse causality and clarify the relationship of PFAS co-exposures with the specific metabolic disorder.

Environmental and dietary exposure to 24 polycyclic aromatic hydrocarbons in a typical Chinese coking plant

Polycyclic aromatic hydrocarbons (PAHs), known for their health risks, are prevalent in the environment, with the coking industry being a major source of their emissions. To bridge the knowledge gap concerning the relationship between environmental and dietary PAH exposure, we explore this complex interplay by investigating the dietary exposure characteristics of 24 PAHs within a typical Chinese coking plant and their association with environmental pollution. Our research revealed Nap and Fle as primary dietary contaminants, emphasizing the significant influence of soil and atmospheric pollution on PAH exposure. We subjected our data to non-metric multidimensional scaling (NMDS), Spearman correlation analysis, Lasso regression, and Weighted Quantile Sum (WQS) regression to delve into this multifaceted phenomenon. NMDS reveals that dietary PAH exposure, especially within the high molecular weight (HMW) group, is common both within and around the coking plant. This suggests that meals prepared within the plant may be contaminated, posing health risks to coking plant workers. Furthermore, our assessment of dietary exposure risk highlights Nap and Fle as the primary dietary contaminants, with BaP and DahA raising concerns due to their higher carcinogenic potential. Our findings indicate that dietary exposure often exceeds acceptable limits, particularly for coking plant workers. Correlation analyses uncover the dominant roles of soil and atmospheric pollution in shaping dietary PAH exposure. Soil contamination significantly impacts specific PAHs, while atmospheric pollution contributes to others. Additionally, WQS regression emphasizes the substantial influence of soil and drinking water on dietary PAHs. In summary, our study sheds light on the dietary exposure characteristics of PAHs in a typical Chinese coking plant and their intricate interplay with environmental factors. These findings underscore the need for comprehensive strategies to mitigate PAH exposure so as to safeguard both human health and the environment in affected regions.

Household Air Pollution and Child Lung Function: The Ghana Randomized Air Pollution and Health Study

Rationale: The impact of a household air pollution (HAP) stove intervention on child lung function has been poorly described. Objectives: To assess the effect of a HAP stove intervention for infants prenatally to age 1 on, and exposure-response associations with, lung function at child age 4. Methods: The Ghana Randomized Air Pollution and Health Study randomized pregnant women to liquefied petroleum gas (LPG), improved biomass, or open-fire (control) stove conditions through child age 1. We quantified HAP exposure by repeated maternal and child personal carbon monoxide (CO) exposure measurements. Children performed oscillometry, an effort-independent lung function measurement, at age 4. We examined associations between Ghana Randomized Air Pollution and Health Study stove assignment and prenatal and infant CO measurements and oscillometry using generalized linear regression models. We used reverse distributed lag models to examine time-varying associations between prenatal CO and oscillometry. Measurements and Main Results: The primary oscillometry measure was reactance at 5 Hz, X5, a measure of elastic and inertial lung properties. Secondary measures included total, large airway, and small airway resistance at 5 Hz, 20 Hz, and the difference in resistance at 5 Hz and 20 Hz (R5, R20, and R5-20, respectively); area of reactance (AX); and resonant frequency. Of the 683 children who attended the lung function visit, 567 (83%) performed acceptable oscillometry. A total of 221, 106, and 240 children were from the LPG, improved biomass, and control arms, respectively. Compared with control, the improved biomass stove condition was associated with lower reactance at 5 Hz (X5 z-score: β = -0.25; 95% confidence interval [CI] = -0.39, -0.11), higher large airway resistance (R20 z-score: β = 0.34; 95% CI = 0.23, 0.44), and higher AX (AX z-score: β = 0.16; 95% CI = 0.06, 0.26), which is suggestive of overall worse lung function. The LPG stove condition was associated with higher X5 (X5 score: β = 0.16; 95% CI = 0.01, 0.31) and lower small airway resistance (R5-20 z-score: β = -0.15; 95% CI = -0.30, 0.0), which is suggestive of better small airway function. Higher average prenatal CO exposure was associated with higher R5 and R20, and distributed lag models identified sensitive windows of exposure between CO and X5, R5, R20, and R5-20. Conclusions: These data support the importance of prenatal HAP exposure on child lung function. Clinical trial registered with www.clinicaltrials.gov (NCT01335490).

Alterations in sperm DNA methylation may as a mediator of paternal air pollution exposure and offspring birth outcomes: Insight from a birth cohort study

Paternal exposure to environmental risk factors influences the offspring health. This study aimed to evaluate the association between paternal air pollution exposure mediated by sperm DNA methylation and adverse birth outcomes in offspring. We recruited 1607 fertile men and their partners from 2014 to 2016 and collected semen samples to detect sperm DNA methylation. Multivariate linear regression and weighted quantile sum regression models were used to assess the associations between paternal air pollution exposure and offspring birth outcomes. A critical exposure window was identified. Reduced representation bisulfite sequencing was used to detect sperm DNA methylation. The results demonstrated that high paternal exposure to PM2.5 (β = -211.31, 95% CI: (-386.37, -36.24)), PM10 (β = -178.20, 95% CI: (-277.13, -79.27)), and NO2 (β = -84.22, 95% CI: (-165.86, -2.57)) was negatively associated with offspring's birthweight, especially in boys. Additionally, an early exposure window of 15-69 days before fertilization was recognized to be the key exposure window, which increased the risk of low birth weight and small for gestational age. Furthermore, paternal co-exposure to six air pollutants contributed to lower birthweight (β = -51.91, 95% CI: (-92.72, -11.10)) and shorter gestational age (β = -1.72, 95% CI: (-3.26, -0.17)) and PM2.5 was the most weighted pollutant. Paternal air pollution exposure resulted in 10,328 differentially methylated regions and the IGF2R gene was the key gene involved in the epigenetic process. These differentially methylated genes were predominantly associated with protein binding, transcriptional regulation, and DNA templating. These findings indicate that spermatogenesis is a susceptible window during which paternal exposure to air pollution affects sperm DNA methylation and the birth outcomes of offspring.

Serum HDL partially mediates the association between exposure to volatile organic compounds and kidney stones: A nationally representative cross-sectional study from NHANES

Environmental exposure to volatile organic compounds (VOCs) is ubiquitous, and this study explored whether exposure to VOCs is associated with the risk of kidney stones. We performed a nationally representative US cross-sectional study using data from five survey cycles (2011-2020) of the National Health and Nutrition Examination Survey (NHANES) program. Exposure to VOCs was determined by urine creatinine-corrected metabolites of VOCs (mVOCs). In total 5505 participants and 15 urine mVOCs were included for analysis, and the prevalence of kidney stones was 9.57 % (527/5505). Multivariable logistic regression showed that urine AMCC (parent VOCs (pVOCs): N, N-Dimethylformamide), 3,4-MHA (pVOCs: xylene), MA (pVOCs: ethylbenzene; styrene), DHBMA (pVOCs: 1,3-butadiene), HMPMA (pVOCs: crotonaldehyde) and 2HPMA (pVOCs: propylene oxide) were significantly associated with an increased risk of kidney stones in US general population. Sub-analysis revealed that there was a more pronounced association in women and the overweight/obesity group (body mass index ≥ 25). Moreover, the weighted quantile sum (WQS) regression model and the Bayesian kernel machine regression (BKMR) model consistently identified a positive association between co-exposure to VOCs and the risk of kidney stones, in which AMCC played the most important role among the 15 mVOCs. Mediation analysis further identified serum high-density lipoprotein cholesterol (HDL) as a mediator of the association between VOC co-exposure and kidney stones. Our study draws attention to the previously unknown positive associations between non-occupational VOC exposure and the risk of kidney stones in the general population. However, further studies are required to clarify the existence of such causation.

Cumulative and lagged effects of varying-sized particulate matter exposure associates with toddlers' gut microbiota

Particulate matter (PM) is an important component of air pollutants and is associated with various health risks. However, the impact of PM on toddlers' gut microbiota is rarely investigated. This study aimed to assess the cumulative and lagged effects of varying-sized PMs on toddlers' gut microbiota. We collected demographic information, stool samples, and exposure to PM from 36 toddlers aged 2-3 years. The toddlers were divided into warm season group and cooler season group according to the collection time of stool samples. The gut microbiota was processed and analyzed using 16S rRNA V3-V4 gene regions. The concentration of PM was calculated using China High Air Pollutants (CHAP) database. To assess the mixed effects of varying-sized PM, multiple-PM models were utilized. There were significant differences between the community composition, α- and β-diversity between two groups. In multiple-PM models, there was a significant effect of weight quantile sum (PM1, PM2.5, and PM10) on α-diversity indices. In weight quantile sum models, after adjusting for a priori confounders, we found a negative effect of weight quantile sum on Enterococcus (β = -0.134, 95% CI -0.263 to -0.006), positive effects of weight quantile sum on unclassified_f__Ruminococcaceae (β = 0.247, 95% CI 0.102 to 0.393), Ruminococcus_1 (β = 0.444, 95% CI 0.238 to 0.650), unclassified_f__Lachnospiraceae (β = 0.278, 95% CI 0.099 to 0.458), and Family_XIII_AD_3011_group (β = 0.254, 95% CI 0.086 to 0.422) in WSG and CSG. In lagged weight quantile sum models, the correlation between lag time PM levels and the gut microbiota showed seasonal trends, and weights of PM changed with lag periods. This is the first study to highlight that cumulative and lagged effects of PMs synergistically affect the diversities (α- and β-diversity) and abundance of the gut microbiota in toddlers. Further research is needed to explore the mediating mechanism of varying-sized PMs exposure on the gut microbiota in toddlers.

Identifying sensitive windows of prenatal household air pollution on birth weight and infant pneumonia risk to inform future interventions

BACKGROUND

Prenatal household air pollution impairs birth weight and increases pneumonia risk however time-varying associations have not been elucidated and may have implications for the timing of public health interventions.

METHODS

The Ghana Randomized Air Pollution and Health Study (GRAPHS) enrolled 1,414 pregnant women from Kintampo, Ghana and measured personal carbon monoxide (CO) exposure four times over pregnancy. Birth weight was measured within 72-hours of birth. Fieldworkers performed weekly pneumonia surveillance and referred sick children to study physicians. The primary pneumonia outcome was one or more physician-diagnosed severe pneumonia episode in the first year of life. We employed reverse distributed lag models to examine time-varying associations between prenatal CO exposure and birth weight and infant pneumonia risk.

RESULTS

Analyses included n = 1,196 mother-infant pairs. In models adjusting for child sex; maternal age, body mass index (BMI), ethnicity and parity at enrollment; household wealth index; number of antenatal visits; and evidence of placental malaria, prenatal CO exposures from 15 to 20 weeks gestation were inversely associated with birth weight. Sex-stratified models identified a similar sensitive window in males and a window at 10-weeks gestation in females. In models adjusting for child sex, maternal age, BMI and ethnicity, household wealth index, gestational age at delivery and average postnatal child CO exposure, CO exposure during 34-39 weeks gestation were positively associated with severe pneumonia risk, especially in females.

CONCLUSIONS

Household air pollution exposures in mid- and late- gestation are associated with lower birth weight and higher pneumonia risk, respectively. These findings support the urgent need for deployment of clean fuel stove interventions beginning in early pregnancy.

Phthalate exposure in the neonatal intensive care unit is associated with development of bronchopulmonary dysplasia

OBJECTIVE

Bronchopulmonary dysplasia (BPD) is a serious yet common morbidity of preterm birth. Although prior work suggests a possible role for phthalate exposure in the development of BPD, no study has rigorously evaluated this. Our objective was to determine whether hospital-based phthalate exposure is associated with the development of BPD and to identify developmental windows sensitive to exposure.

STUDY DESIGN

This is a prospective multicenter cohort study of 360 preterm infants born at 23-33 weeks gestation participating in the Developmental Impact of NICU Exposures (DINE) cohort. 939 urine specimens collected during the NICU stay were analyzed for biomarkers of phthalate exposure by liquid chromatography with tandem mass spectrometry. The modified Shennan definition was used to diagnose bronchopulmonary dysplasia. Reverse distributed-lag modeling identified developmental windows sensitive to specific phthalate exposure, controlling for relevant covariates including sex and respiratory support.

RESULTS

Thirty-five percent of participants were diagnosed with BPD. Exposure to specific phthalate mixtures at susceptible points in preterm infant development are associated with later diagnosis of BPD in models adjusted for use of respiratory support. The weighted influence of specific phthalate metabolites in the mixtures varied by sex. Metabolites of di(2-ethylhexyl) phthalate, a phthalate previously linked to neonatal respiratory support equipment, drove this association, particularly among female infants, at 26- to 30-weeks post-menstrual age.

CONCLUSIONS

This is the largest and only multi-site study of NICU-based phthalate exposure and clinical impact yet reported. In well-constructed models accounting for infant sex and respiratory support, we found a significant positive association between ultimate diagnosis of BPD and prior exposure to phthalate mixtures with DEHP predominance at 26- to 30-weeks PMA or 34-36-weeks PMA. This information is critically important as it identifies a previously unrecognized and modifiable contributing factor to BPD.

Individual and joint associations of long-term exposure to air pollutants and cardiopulmonary mortality: a 22-year cohort study in Northern China

Background

Evidence on the associations between long-term exposure to multiple air pollutants and cardiopulmonary mortality is limited, especially for developing regions with higher pollutant levels. We aimed to characterise the individual and joint (multi-pollutant) associations of long-term exposure to air pollutants with cardiopulmonary mortality, and to identify air pollutant that primarily contributes to the mortality risk.

Methods

We followed 37,442 participants with a mean age of 43.5 years in four cities in northern China (Tianjin, Shenyang, Taiyuan, and Rizhao) from January 1998 to December 2019. Annual particulate matter (PM) with diameters ≤2.5 μm (PM2.5), ≤10 μm (PM10), sulfur dioxide (SO2) and nitrogen dioxide (NO2) were estimated using daily average values from satellite-derived machine learning models and monitoring stations. Time-varying Cox proportional hazards model was used to evaluate the individual association between air pollutants and mortality from non-accidental causes, cardiovascular diseases (CVDs), non-malignant respiratory diseases (RDs) and lung cancer, accounting for demographic and socioeconomic factors. Effect modifications by age, sex, income and education level were also examined. Quantile-based g-Computation integrated with time-to-event data was additionally applied to evaluate the co-effects and the relative weight of contributions for air pollutants.

Findings

During 785,807 person-years of follow-up, 5812 (15.5%) died from non-accidental causes, among which 2932 (7.8%) were from all CVDs, 479 (1.3%) from non-malignant RDs, and 552 (1.4%) from lung cancer. Long-term exposure to PM10 (mean [baseline]: 136.5 μg/m3), PM2.5 (mean [baseline]: 70.2 μg/m3), SO2 (mean [baseline]: 113.0 μg/m3) and NO2 (mean [baseline]: 39.2 μg/m3) were adversely and consistently associated with all mortality outcomes. A 10 μg/m3 increase in PM2.5 was associated with higher mortality from non-accidental causes (hazard ratio 1.20; 95% confidence interval 1.17-1.23), CVDs (1.23; 1.19-1.28), non-malignant RDs (1.37; 1.25-1.49) and lung cancer (1.14; 1.05-1.23). A monotonically increasing curve with linear or supra-linear shape with no evidence of a threshold was observed for the exposure-response relationship of mortality with individual or joint exposure to air pollutants. PM2.5 consistently contributed most to the elevated mortality risks related to air pollutant mixture, followed by SO2 or PM10.

Interpretation

There was a strong and positive association of long-term individual and joint exposure to PM10, PM2.5, SO2, and NO2 with mortalities from non-accidental causes, CVDs, non-malignant RDs and lung cancer in high-exposure settings, with PM2.5 potentially being the main contributor. The shapes of associations were consistent with a linear or supra-linear exposure-response relationship, with no lower threshold observed within the range of concentrations in this study.

Funding

National Key Research and Development Program of China, the China Scholarship Council, the National Natural Science Foundation of China, Natural Science Foundation of Guangdong Province.

A cross-sectional study of the association between heavy metals and pan-cancers associated with sex hormones in NHANES 1999-2018

Given the complexity of tumorigenesis, numerous studies have also shown that excessive exposure to heavy metals increases the risk of cancers and disrupts the secretion of sex hormones. However, the specific effects of heavy metals on cancers remain to be proven. To confirm the association between heavy metals and pan-cancer sex hormone levels among adults, 94,337 individuals from the National Health and Nutrition Examination Survey were assessed. We examined the associations between pan-cancers associated with sex hormones (ovarian, testicular, breast, and prostate cancers) and heavy metals in blood/urine. The methods (the WQS (weighted quantile sums) and SVYGLM (survey generalized linear model) regressions) were used to evaluate the association between sex hormone-related cancers and each metal category by incorporating covariates. To evaluate the overall effect of heavy metals and detect the dose-response relationship between the prevalence of pan-cancers associated with sex hormones and heavy metals, RCS (restricted cubic splines) were applied. Environmental exposure to heavy metals may be associated with pan-cancers associated with sex hormones in adults in the USA. Prostate cancer was inversely associated with blood cadmium while positively associated with blood lead, urinary tin, and thallium. Breast cancer was inversely associated with blood lead. Ovarian cancer was positively associated with blood cadmium. We also found a non-linear dose-response relationship between pan-cancers associated with sex hormones and heavy metals, which was non-parametric, using RCS models. The OR for breast cancer decreased along with the increase in lead concentration under approximately 20 µg/dl, while the OR for prostate cancer increased between urine thallium levels of approximately 0.17-1.1 ng/ml. Pan-cancers associated with sex hormones are associated with exposure to heavy metals. Considering the design of the NHANES study, further studies need to be conducted on other nationally representative surveys.

Deciduous tooth biomarkers reveal atypical fetal inflammatory regulation in autism spectrum disorder

Atypical regulation of inflammation has been proposed in the etiology of autism spectrum disorder (ASD); however, measuring the temporal profile of fetal inflammation associated with future ASD diagnosis has not been possible. Here, we present a method to generate approximately daily profiles of prenatal and early childhood inflammation as measured by developmentally archived C-reactive protein (CRP) in incremental layers of deciduous tooth dentin. In our discovery population, a group of Swedish twins, we found heightened inflammation in the third trimester in children with future ASD diagnosis relative to controls (n = 66; 14 ASD cases; critical window: -90 to -50 days before birth). In our replication study, in the US, we observed a similar increase in CRP in ASD cases during the third trimester (n = 47; 23 ASD cases; -128 to -21 days before birth). Our results indicate that the third trimester is a critical period of atypical fetal inflammatory regulation in ASD.

Urinary phenols and parabens metabolites associated with cardiovascular disease among adults in the United States

The field of environmental health has begun to examine the effects of higher-order chemical combinations. The current literature lacks studies exploring associations between multiple organic chemical mixtures and cardiometabolic diseases (CVDs). This study aimed to evaluate associations between urinary phenols, parabens metabolites, and total and individual CVDs among a nationally representative sample of adults in the US. This cross-sectional study analyzed 7 urinary chemicals detected among the general population from the 2005-2016 National Health and Nutrition Examination Survey (NHANES, n=10,428). Multivariate logistic regression and weighted quantile sum (WQS) regression were applied to examine relationships between phenols and parabens metabolites, alone and in combination, and total and individual CVDs prevalence. Compared with the lowest quartile, URBPA (OR: 1.52; 95% CI: 1.20-1.91; P=0.001) levels in the highest quartile were independently associated with increased total CVD. The WQS index of phenols and parabens mixtures were independently correlated with total CVD (adjusted odds ratios [OR]: 1.16; 95% confidence interval [CI]:1.06-1.28; P=0.002), angina (adjusted OR: 1.30; 95% CI: 1.07-1.59; P=0.009), and heart attack (adjusted OR: 1.30; 95% CI: 1.12-1.51, P<0.001). Urinary bisphenol A (URBPA, weight=0.636) was the most heavily weighted component in the total CVD model. Restricted cubic spline regression demonstrated positive correlations and nonlinear associations between URBPA and both total CVD (P for nonlinearity=0.032) and individual CVD (heart attack; P for nonlinearity=0.031). Our findings suggested that high combined levels of phenols, and parabens are associated with an increased CVD risk, with URBPA contributing the highest risk.

Concurrent dietary intake to nitrate, thiocyanate, and perchlorate is negatively associated with hypertension in adults in the USA

We aimed to comprehensively evaluate the association of urinary nitrate, thiocyanate, and perchlorate metabolites with hypertension among a nationally representative sample of the US adult population. This cross-sectional study investigated data from 15,717 adults aged more than 20 years obtained from the National Health and Nutritional Examination Survey (NHANES) for the years 2005-2016. In the survey, urinary levels of nitrate, thiocyanate, and perchlorate were measured using ion chromatography combined with electrospray tandem mass spectrometry. Blood pressure was calculated as the mean of three measurements. Hypertension was defined as (a) systolic BP ≥130 and/or diastolic BP ≥80 mmHg and/or (b) self-report. Multivariate logistic regression and weighted quantile sum (WQS) regression models were applied to estimate the association between exposure to multiple inorganic anions and hypertension. Restricted cubic spline (RCS) regressions were fitted to discern the potential relationship between the anion exposure and hypertension. These innovation methods used to support our results. Overall, 7533 (49.95%) people with and 7638 (50.35%) without hypertension were included in this study. In the multivariable-adjusted logistic regression models, urinary nitrate (P < 0.001) and perchlorate (P < 0.001) were independently negatively associated with increased occurrence of hypertension, while urinary thiocyanate was insignificantly associated with hypertension (P = 0.664). The WQS regression index showed that, in combination, the three inorganic anions mixture were negatively correlated with hypertension (adjusted OR 0.89; 95% CI 0.83-0.95, P < 0.001). Urinary nitrate was the most heavily weighted component in the hypertension model (weight = 0.784). RCS regression demonstrated that nitrate (nonlinearity P = 0.205) and perchlorate (nonlinearity P = 0.701) were linearly associated with decreased occurrence of hypertension. Concurrent exposure to nitrate, thiocyanate, and perchlorate is associated with a decreased risk of hypertension, with the greatest influence coming from nitrate probably; urinary specific thiocyanate alone had an insignificant association with hypertension.

NICU-based stress response and preterm infant neurobehavior: exploring the critical windows for exposure

BACKGROUND

Exposure to maternal stress in utero negatively impacts cognitive and behavioral outcomes of children born at term. The neonatal intensive care unit (NICU) can be stressful for preterm infants during a developmental period corresponding to the third trimester of gestation. It is unknown whether stress in the NICU contributes to adverse neurodevelopment among NICU graduates. The aim was to examine the association between salivary cortisol and early neurodevelopment in preterm infants.

METHODS

We examined the association between cortisol levels during the NICU hospitalization and subsequent performance on the NICU Network Neurobehavioral Scales (NNNS), estimating time-specific associations and considering sex differences.

RESULTS

Eight hundred and forty salivary cortisol levels were measured from 139 infants. Average cortisol levels were inversely associated with NNNS Regulation scores for both male and female infants (β = -0.19; 95% CI: -0.44, -0.02). Critical developmental windows based on postmenstrual age were identified, with cortisol measured <30 weeks PMA positively associated with Habituation and Lethargy scores (β = 0.63-1.04). Critical developmental windows based on chronological age were identified, with cortisol measured in the first week of life inversely associated with Attention score (β = -1.01 for females; -0.93 for males).

CONCLUSIONS

Stress in the NICU at specific developmental time points may impact early preterm infant neurodevelopment.

IMPACT

Stress in the neonatal intensive care unit can impact the neurodevelopmental trajectory of premature infants. The impact of stress is different at different points in development. The impact of stress is sexually dimorphic.

Risk assessment and dose-effect of co-exposure to benzene, toluene, ethylbenzene, xylene, and styrene (BTEXS) on pulmonary function: A cross-sectional study

Inhalation is the most frequent route and the lung is the primary damaged organ for human exposure to benzene, toluene, ethylbenzene, xylene, and styrene (BTEXS). However, there is limited information on the risk and dose-effect of the BTEXS mixture on pulmonary function, particularly the overall effect. We conducted a cross-sectional study in a petrochemical plant in southern China. Spirometry and cumulative exposure dose (CED) of BTEXS were used to measure lung function and exposure levels for 635 workers in 2020, respectively. Forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV₁) were tested and interpreted as percentages to predicted values [FVC or FEV₁% predicted], and FEV₁ to FVC ratio [FEV₁/FVC (%)]. We found the reduction in FVC% predicted and the risk of lung ventilation dysfunction (LVD) and its two subtypes (mixed and restrictive ventilation dysfunction, MVD, and MVD) were significantly associated with BTEXS individuals. In addition, pulmonary function damage associated with BTEXS was modified by the smoking status and age. Generalized weighted quantile sum (gWQS) regressions were used to estimate the overall dose-effect on lung function damage induced by the BTEXS mixture. Our results show wqs, an index of weighted quartiles for BTEXS, was potentially associated with the reduction in FVC and FEV₁% predicted with the coefficients [95% confidence intervals (CI)] between -1.136 (-2.202, -0.070) and -1.230 (-2.265, -0.195). Odds ratios (ORs) and 95% CIs for the wqs index of LVD, MVD, and RVD were 1.362 (1.129, 1.594), 1.323 (1.084, 1.562), and 1.394 (1.096, 1.692), respectively. Furthermore, xylene, benzene, and toluene in the BTEXS mixture potentially contribute to the development of lung function impairment. Our novel findings demonstrated the dose-response relationships between pulmonary function impairment and the BTEXS mixture and disclosed the potential key pollutants in the BTEXS mixture.

CRITICAL WINDOW VARIABLE SELECTION FOR MIXTURES: ESTIMATING THE IMPACT OF MULTIPLE AIR POLLUTANTS ON STILLBIRTH

Understanding the role of time-varying pollution mixtures on human health is critical as people are simultaneously exposed to multiple pollutants during their lives. For vulnerable subpopulations who have well-defined exposure periods (e.g., pregnant women), questions regarding critical windows of exposure to these mixtures are important for mitigating harm. We extend critical window variable selection (CWVS) to the multipollutant setting by introducing CWVS for mixtures (CWVSmix), a hierarchical Bayesian method that combines smoothed variable selection and temporally correlated weight parameters to: (i) identify critical windows of exposure to mixtures of time-varying pollutants, (ii) estimate the time-varying relative importance of each individual pollutant and their first order interactions within the mixture, and (iii) quantify the impact of the mixtures on health. Through simulation we show that CWVSmix offers the best balance of performance in each of these categories in comparison to competing methods. Using these approaches, we investigate the impact of exposure to multiple ambient air pollutants on the risk of stillbirth in New Jersey, 2005-2014. We find consistent elevated risk in gestational weeks 2, 16-17, and 20 for non-Hispanic Black mothers, with pollution mixtures dominated by ammonium (weeks 2, 17, 20), nitrate (weeks 2, 17), nitrogen oxides (weeks 2, 16), PM2.5 (week 2), and sulfate (week 20). The method is available in the R package CWVSmix.

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.

Associating multiple mycotoxin exposure and health outcomes: current statistical approaches and challenges

Mycotoxin contamination is a global challenge to food safety and population health. A diversity of adverse effects in human health such as organ damage, immunity disorders and carcinogenesis are attributed to acute and chronic exposure to mycotoxins. While there is a high likelihood of mycotoxin co-occurrence in the daily diet, multiple mycotoxin exposures represent a considerable challenge in understanding the accumulative effects of groups of exposures on health outcomes. Nevertheless, previous studies on mycotoxin exposure-health outcome associations have focused on a single or a limited number of exposures. To guide multi-exposure assessment, careful considerations of statistical approaches available are required. In addition, the issue of multicollinearity in high-dimensional settings of multiple exposure analysis underlies the controversy surrounding the reliability and consistency of statistical conclusions about the exposure-health outcome associations. Conventional approaches such as generalised linear regressions (GLR) in conjunction with regularisation methods, including ridge regression, lasso and elastic net, offer some clear advantages in terms of results’ interpretation and model selection. However, when highly-correlated variables are observed, these methods have shown a low specificity in variable selection. Principal component analysis (PCA) that has been widely used as a dimensionality reduction technique also has the limitation to identify important predictor variables as this approach may overlook the associations between certain components and health outcomes. Recently, some alternative approaches have been introduced to address the issues of high dimensionality and highly-correlated data in the context of epidemiological and environmental research. Two of the noticeable approaches are weighted quantile sum regression (WQSR) and Bayesian kernel machine regression (BKMR). Combining different methods of inference allows us to interpret the role of certain exposures, their interactions and the combined effects on human health under diverse statistical perspectives, which ultimately facilitate the construction of the toxicological profile of multiple mycotoxins’ exposure.

Ambient Air Pollutants and Traffic Factors Were Associated with Blood and Urine Biomarkers and Asthma Risk

The UK Biobank (UKBB) is a large population-based cohort that provides a unique opportunity to study the association between environmental exposure and biomarkers and to identify biomarkers as potential instruments for assessing exposure dose, health damage, and disease risks. On 462 063 participants of European ancestry, we characterized the relationship of 38 disease-relevant biomarkers, asthma diagnosis, ambient pollution, traffic factors, and genetic background. The air pollutant exposure on the UKBB cohort was fairly low (e.g., mean PM_2.5 concentration at 10.0 μg/m³). Nevertheless, 30 biomarkers were in association with at least one environmental factor; e.g., C-reactive protein levels were positively associated with NO (p_adj = 2.99 × 10^-4), NO₂ (p_adj = 4.15 × 10^-4), and PM_2.5 (p_adj = 1.92 × 10^-6) even after multiple testing adjustment. Asthma diagnosis was associated with four pollutants (NO, NO₂, PM_2.5, and PM₁₀). The largest effect size was observed in PM_2.5, where a 5 μg/m³ increment of exposure was associated with a 1.52 increase in asthma diagnosis (p = 4.41 × 10^-13). Further, environmental exposure and genetic predisposition influenced biomarker levels and asthma diagnosis in an additive model. The exposure-biomarker associations identified in this study could serve as potential indicators for environmental exposure induced health damages. Our results also shed light on possible mechanisms whereby environmental exposure influences disease-causing biomarkers and in turn increases disease risk.

How to investigate human health effects related to exposure to mixtures of per- and polyfluoroalkyl substances: A systematic review of statistical methods

BACKGROUND

Humans are exposed to several per- and polyfluoroalkyl substances (PFAS) daily; however, most previous studies have focused on individual PFAS. Although attention to effects of exposure to mixtures of PFAS has grown in recent years, there is no consensus on the appropriate statistical methods that can be used to assess their combined effect on human health.

OBJECTIVES

We aim to perform a comprehensive review of the statistical methods used in the existing studies which evaluate the association between exposure to mixtures of PFAS and any adverse human health effect.

METHODS

The online databases PubMed, Embase and Scopus were searched for eligible studies, published during the last ten years (last search performed on April 08, 2021). Covidence software was used by two different reviewers to perform a title/abstract screening, followed by a full text revision of the selected papers.

RESULTS

A total of 3640 papers were identified, and after the screening process, 53 papers were included in the current review. Most of the studies were published between 2019 and 2021 and were conducted mainly in North America and Europe; more than half of the studies (28 out of 53) were conducted on mother and child pairs. WQS (Weighted Quantile Sum) Regression and BKMR (Bayesian Kernel Machine Regression) were used in 36 out of 53 papers to model mixtures' effects. Health outcomes included in the studies are immunotoxicity (n = 8), fetal development (n = 7), neurodevelopment (n = 9), reproductive hormones (n = 6), thyroid hormones (n = 7), outcomes related to metabolic pathways (n = 16).

CONCLUSION

Studies on human exposure to PFAS as complex mixtures and health consequences have substantially increased in the last few years. Based on our findings, we propose that addressing risk from PFAS mixtures will likely require combinations of approaches and implementation of constantly evolving statistical methods. Specific guidelines and tools for quality assessment and publication of mixture observational studies are warranted.

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.

Multiple statistical models reveal specific volatile organic compounds affect sex hormones in American adult male: NHANES 2013-2016

BACKGROUND

Some VOCs are identified as endocrine-disrupting chemicals (EDCs), interfering with the effect of sex hormones. However, no studies focused on the common spectrum of environmental VOCs exposure affecting sex hormones in the average male population.

OBJECTIVES

We aimed to explore the association between VOCs and sex hormones in American adult males using multiple statistical models.

METHODS

The generalized linear (GLM), eXtreme Gradient Boosting (XGBoost), weighted quantile sum (WQS), Bayesian kernel machine regression (BKMR) and stratified models were used to evaluate the associations between Specific Volatile Organic Compounds and sex hormones in American adult male from NHANES 2013-2016.

RESULTS

Pearson correlation model revealed the potential co-exposure pattern among VOCs. XGBoost algorithm models and the WQS model suggested the relative importance of VOCs. BKMR models reveal that co-exposure to the VOCs was associated with increased Testosterone (TT), Estradiol (E₂), SHBG and decreased TT/E₂. GLM models revealed specific VOC exposure as an independent risk factor causing male sex hormones disorders. Stratified analysis identified the high-risk group on the VOCs exposures. We found Blood 2,5-Dimethylfuran in VOCs was the most significant effect on sex hormones in male. Testosterone increased by 213.594 (ng/dL) (124.552, 302.636) and estradiol increased by 7.229 (pg/mL) for each additional unit of blood 2,5-Dimethylfuran (ng/mL).

CONCLUSION

This study is an academic illustration of the association between VOCs exposure and sex hormones, suggesting that exposure to VOCs might be associated with sex hormone metabolic disorder in American adult males.

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.

Metal mixtures and neurodevelopment: recent findings and emerging principles

Children are constantly exposed to a wide range of environmental factors including essential and non-essential metals. In recent years, the mixtures paradigm has emerged to foster the examination of combined effects that emerge from exposures to multiple elements. In this review, we summarized recent literature studying the relationship between prenatal and childhood metal mixtures with neurodevelopmental outcomes. Our review highlights two basic principles to emerge from this approach. First, recent findings emphasize that the effect of a given exposure is contextual and may be dependent on past or concurrent metal exposures. Second, the timing of exposures is equally critical to the mixture composition in determining neurodevelopmental effects. Our discussion emphasizes how these principles may apply to future exposure-related neurodevelopmental studies.