A Benchmark Dose Analysis for Maternal Pregnancy Urine-Fluoride and IQ in Children

Maternal Urinary Fluoride Levels of a Large Pregnancy Cohort in the United States: Findings from the ADORE Study

BACKGROUND

Emerging evidence has suggested negative associations between maternal urinary fluoride adjusted for specific gravity (MUFsg) and offspring intelligence quotient (IQ). Two prior studies report the MUFsg of pregnant women in the US, both in California, and more information is needed on population levels of MUFsg.

OBJECTIVES

The primary objective was to measure MUFsg in a large pregnancy cohort of women recruited from health departments and academic hospitals in Ohio and Kansas. A secondary objective was to compare associations between water fluoridation level and estimated fluoride intake from tap water and MUFsg.

METHODS

Pregnant women (n = 965 ) from the ADORE (Assessment of DHA on Reducing Early Preterm Birth) cohort provided a urine sample and dietary assessment at enrollment between 14 and 20 wk gestation. MUFsg was measured by fluoride-sensitive electrode and corrected for specific gravity. Water fluoridation levels were obtained for public water systems (PWS), matched to participant residence and multiplied by their tap water intake from dietary assessment. The association between MUFsg and water fluoridation level was estimated using a generalized linear model with gamma distribution and log link.

RESULTS

MUFsg (median: 1.0 mg / L ; Q1, Q3: 0.6, 1.5) was correlated with PWS fluoridation (r s = 0.30 ; p < 0.01 ) and self-reported tap water consumption (r s = 0.29 ; p < 0.01 ). For 87% of the cohort, MUFsg was above the 0.45 mg / L safety benchmark for pregnancy proposed in a previous study. Similarly, 76.7% lived in areas with PWS fluoridation ≥ 0.7 mg / L . The median MUFsg (1.0 mg / L ; Q1, Q3: 0.7, 1.5) of those living in areas with a PWS fluoridation level ≥ 0.7 mg / L was higher than the median MUFsg (0.8 mg / L ; Q1, Q3: 0.5, 1.2) of women living in areas with PWS fluoridation < 0.7 mg / L (p < 0.01 ).

DISCUSSION

MUFsg in this population of midwestern US women exceeds the safety benchmark for pregnancy. While we cannot account for all sources of fluoride, MUFsg was correlated to PWS fluoridation. Because so many exceeded the safety benchmark for MUFsg, there is a need for MUFsg evaluation in other US regions, especially where the PWS fluoridation exceeds US Department of Health and Human Services recommendations (≥ 0.7 mg / L ). https://doi.org/10.1289/EHP14711.

Associations of gestational and childhood exposure to lead, cadmium, and fluoride with cognitive abilities, behavior, and social communication at 4 years of age: NICE birth cohort study

BACKGROUND

Early-life lead exposure affects cognitive development and emerging evidence suggests similar effects of cadmium and fluoride.

OBJECTIVE

To assess the impact of gestational and childhood exposure to lead, cadmium, and fluoride on cognitive abilities and behavioral and social communication problems.

METHODS

We studied 470 pregnant women (gestational week 29) and their 4-year-old children from the NICE cohort in northern Sweden. Concentrations of erythrocyte lead and cadmium and urinary cadmium were measured using inductively coupled plasma mass spectrometry and urinary fluoride with an ion-selective electrode. Urinary concentrations were specific-gravity adjusted. Associations of log2-transformed exposure concentrations with cognitive abilities (full-scale IQ and verbal comprehension by Wechsler Preschool and Primary Scale of Intelligence-Fourth Edition), behavioral problems (Child Behavior Checklist), and social communication (Social Responsiveness Scale-Second Edition) were evaluated with multivariable-adjusted linear regression analysis.

RESULTS

Both gestational and cord erythrocyte lead concentrations were non-significantly inversely associated with child cognitive abilities (full-scale IQ: B [95%CI]: -1.2 [-2.9, 0.5] and -1.6 [-3.7, 0.4], respectively; per doubling of exposure). Similarly, both gestational and child urinary cadmium were inversely associated with cognitive abilities (full-scale IQ: -1.1 [-2.5, 0.3] and -1.1 [-2.5, 0.4], verbal comprehension: -1.2 [-3.1, 0.6] and -1.4 [-3.4, 0.6], respectively). Urinary fluoride concentrations showed no association with cognitive abilities. However, gestational fluoride was associated with increasing externalizing problems (0.9 [-0.3, 2.0]) and ADHD raw scores (0.3 [0.0, 0.6]). Childhood erythrocyte lead and urinary cadmium were non-significantly associated with increased behavioral problems (lead with total problems: 1.2 [-0.4, 2.9] and internalizing problems: 1.5 [-0.4, 3.4]; cadmium with externalizing problems: 1.1 [-0.2, 2.4]).

CONCLUSION

Despite non-significant associations, both lead and cadmium exposure showed consistent inverse associations with cognitive abilities at 4 years, whereas associations with behavioral problems were less conclusive, especially for cadmium. Results on fluoride indicated association with externalizing problems, including ADHD, but prevalence of behavioral problems was low, increasing uncertainty.

Focus on cognitive impairment induced by excessive fluoride: An update review

Fluorosis is a global public health concern. Prolonged exposure to excessive fluoride causes fluoride accumulation in the hippocampus, resulting in cognitive dysfunction. Cell death is necessary for maintaining tissue function and morphology, and changes in the external morphology of nerve cells and the function of many internal organelles are typical features of cell death; however, it is also a typical feature of cognitive impairment caused by fluorosis. However, the pathogenesis of cognitive impairment caused by different degrees of fluoride exposure varies. Herein, we provide an overview of cognitive impairment caused by excessive fluoride exposure in different age groups, and the underlying mechanisms for cognitive impairment in various model organisms. The mechanisms underlying these impairments include oxidative stress, synaptic and neurotransmission dysfunction, disruption of mitochondrial and energy metabolism, and calcium channel dysregulation. This study aims to provide potential insights that serve as a reference for subsequent research on the cognitive function caused by excessive fluoride.

Associations between Dietary Patterns, Fluoride Intake and Excretion in Women Exposed to Fluoridated Salt: A Preliminary Study

Abundant information exists on fluoride intake and excretion in populations exposed to fluoridated water, but not fluoridated salt, where fluoride is eaten through a combination of foods and beverages. This study assessed associations between dietary patterns, fluoride intake and excretion in Mexican women exposed to fluoridated salt. We estimated dietary fluoride intake and excretion (mg/day) from 31 women using 24-h recalls (ASA24) and 24-h urine collections (HDMS diffusion method) and assessed agreement among both estimates of exposure with a Bland-Altman plot. Dietary patterns among the sample were explored by Principal Component Analysis and associations between these patterns and both fluoride intake and excretion were estimated. using Quantile Regressions. Median dietary fluoride intake and excretion were 0.95 and 0.90 mg/day, respectively, with better agreement at values below 1.5 mg/day. We identified three dietary patterns: "Urban Convenience", "Plant-based" and "Egg-based". The "Urban Convenience" pattern, characterized by dairy and convenience foods was associated with an increase of 0.25 mg and 0.34 mg of F in the 25th and 50th percentiles of intake respectively, (p < 0.01), and a marginal 0.22 mg decrease in urinary fluoride (p = 0.06). In conclusion, in this sample of Mexican women, a dietary pattern rich in dairy and convenience foods, was associated with both fluoride intake and excretion.

Neurodevelopmental assessments used to measure preschoolers' cognitive development in Latin America: a systematic review

OBJECTIVE

The objective of this study was to systematically review the standardized neurodevelopmental assessments used to study preschool-aged children's cognitive development in Spanish-speaking Latin America.

METHODS

The authors systematically searched PubMed, PsycINFO, and ERIC databases for peer-reviewed articles from Spanish-speaking Latin American countries. Articles were included if they measured cognitive development among children aged 2-6 years using at least one standardized assessment tool; 97 articles were included and reviewed in accordance with PRISMA guidelines to assess their use of these tools.

RESULTS

Ninety-seven studies across 13 countries used a total of 41 assessments to measure cognitive development; most widely used were the Wechsler intelligence scales (n = 46/97), particularly the Wechsler Preschool and Primary Scale of Intelligence and Wechsler Intelligence Scale for Children (n = 23 and 29, respectively). Other common assessments included the McCarthy Scales of Children's Abilities (n = 9), Raven's Progressive Matrices (n = 9), Child Neuropsychological Assessment (n = 8), and Peabody Picture Vocabulary Test (n = 7). In regions where normative data for a given assessment were unpublished, authors commonly used norms from the United States, Mexico, or Spain or did not report standard scores in their analyses.

CONCLUSIONS

The wide range of tools used in these studies presents a challenge for generalizing results when measuring the neurodevelopment of Latin American preschool-aged children. The low availability of normative data for specific regions reveals concerns if some tools are culturally and linguistically appropriate even when Spanish is a common language, particularly in low-resource settings. Future work to forge greater consistency in the use of validated measures, clarity in reporting research methods, and publication of regional normative data would benefit the field.

Water Fluoridation and Birth Outcomes in California

BACKGROUND

There is a lack of research on the relationship between water fluoridation and pregnancy outcomes.

OBJECTIVES

We assessed whether hypothetical interventions to reduce fluoride levels would improve birth outcomes in California.

METHODS

We linked California birth records from 2000 to 2018 to annual average fluoride levels by community water system. Fluoride levels were collected from consumer confidence reports using publicly available data and public record requests. We estimated the effects of a hypothetical intervention reducing water fluoride levels to 0.7  ppm (the current level recommended by the US Department of Health and Human Services) and 0.5  ppm (below the current recommendation) on birth weight, birth-weight-for-gestational age z-scores, gestational age, preterm birth, small-for-gestational age, large-for-gestational age, and macrosomia using linear regression with natural cubic splines and G-computation. Inference was calculated using a clustered bootstrap with Wald-type confidence intervals. We evaluated race/ethnicity, health insurance type, fetal sex, and arsenic levels as potential effect modifiers.

RESULTS

Fluoride levels ranged from 0 to 2.5  ppm , with a median of 0.51  ppm . There was a small negative association on birth weight with the hypothetical intervention to reduce fluoride levels to 0.7  ppm [- 2.2 g ; 95% confidence interval (CI): - 4.4 , 0.0] and to 0.5  ppm (- 5.8 g ; 95% CI: - 10.0 , - 1.6 ). There were small negative associations with birth-weight-for-gestational-age z-scores for both hypothetical interventions (0.7  ppm : - 0.004 ; 95% CI: - 0.007 , 0.000 and 0.5  ppm : - 0.006 ; 95% CI: - 0.013 , 0.000). We also observed small negative associations for risk of large-for-gestational age for both the hypothetical interventions to 0.7  ppm [risk difference  ( RD ) = - 0.001 ; 95% CI: - 0.002 , 0.000 and 0.5  ppm (- 0.001 ; 95% CI: - 0.003 , 0.000)]. We did not observe any associations with preterm birth or with being small for gestational age for either hypothetical intervention. We did not observe any associations with risk of preterm birth or small-for-gestational age for either hypothetical intervention.

CONCLUSION

We estimated that a reduction in water fluoride levels would modestly decrease birth weight and birth-weight-for-gestational-age z-scores in California. https://doi.org/10.1289/EHP13732.

Dose dependence of prenatal fluoride exposure associations with cognitive performance at school age in three prospective studies

BACKGROUND

Fluoride may be a developmental neurotoxicant at elevated exposures. We merged new data from a prospective Odense Child Cohort (OCC) with results from two previous birth cohort studies from Mexico and Canada to characterize the dose-effect relationship in greater detail.

METHODS

The OCC contributed 837 mother-child pairs to the total of >1500. We measured creatinine-adjusted urine-fluoride concentrations in maternal urine samples obtained during late pregnancy. Child IQ was determined at age 7 years using an abbreviated version of the Wechsler Intelligence Scales for Children. Findings from the three cohorts were used to calculate the joint benchmark concentration (BMC) and the lower confidence limit (BMCL) after adjustment for covariables.

RESULTS

In the OCC, urine-fluoride concentrations varied between 0.08 and 3.04 mg/l (median 0.52 mg/l) but were not significantly associated with full-scale IQ at age 7 years (β = 0.08; 95% confidence interval -1.14 to 1.30 for a doubling in exposure). No difference was apparent between boys and girls. In the OCC, the BMC was 0.92 mg/l, with a BMCL of 0.30 mg/l. The joint analysis of all three cohorts showed a statistically significant association between urine-fluoride and IQ, with a BMC of 0.45 mg/l (BMCL, 0.28 mg/l), slightly higher than the BMC previously reported for the two North American cohorts alone.

CONCLUSIONS

As the BMCL reflects an approximate threshold for developmental neurotoxicity, the results suggest that pregnant women and children may need protection against fluoride toxicity.

Systematic review of epidemiological and toxicological evidence on health effects of fluoride in drinking water

INTRODUCTION

Fluoride is a naturally occurring substance that is also added to drinking water, dental hygiene products, and food supplements for preventing dental caries. Concerns have been raised about several other potential health risks of fluoride.

OBJECTIVE

To conduct a robust synthesis of evidence regarding human health risks due to exposure to fluoride in drinking water, and to develop a point of departure (POD) for setting a health-based value (HBV) for fluoride in drinking water.

METHODS

A systematic review of evidence published since recent reviews of human, animal, and in vitro data was carried out. Bradford Hill considerations were used to weigh the evidence for causality. Several key studies were considered for deriving PODs.

RESULTS

The current review identified 89 human studies, 199 animal studies, and 10 major in vitro reviews. The weight of evidence on 39 health endpoints was presented. In addition to dental fluorosis, evidence was considered strong for reduction in IQ scores in children, moderate for thyroid dysfunction, weak for kidney dysfunction, and limited for sex hormone disruptions.

CONCLUSION

The current review identified moderate dental fluorosis and reduction in IQ scores in children as the most relevant endpoints for establishing an HBV for fluoride in drinking water. PODs were derived for these two endpoints, although there is still some uncertainty in the causal weight of evidence for causality for reducing IQ scores in children and considerable uncertainty in the derivation of its POD. Given our evaluation of the overall weight of evidence, moderate dental fluorosis is suggested as the key endpoint until more evidence is accumulated on possible reduction of IQ scores effects. A POD of 1.56 mg fluoride/L for moderate dental fluorosis may be preferred as a starting point for setting an HBV for fluoride in drinking water to protect against moderate and severe dental fluorosis. Although outside the scope of the current review, precautionary concerns for potential neurodevelopmental cognitive effects may warrant special consideration in the derivation of the HBV for fluoride in drinking water.

Association of Dental Fluorosis and Urinary Fluoride with Intelligence among Schoolchildren

Fluoride is present naturally in water and has been used worldwide for the prevention of caries. Several studies conducted in high water fluoride or endemic fluorosis areas reported that fluoride adversely affected children's cognitive function, but some studies had negative findings. This study aimed to assess the relationship between urinary fluoride, dental fluorosis, and intelligence among schoolchildren living in communities with non-fluoridated drinking water. This cross-sectional study was conducted on 562 children aged 6-12 years in Taichung, Taiwan. Each child's urinary fluoride level was determined by a fluoride-ion-selective electrode, and the dental fluorosis condition was evaluated according to the criteria of Dean's Index. The Raven's Colored Progressive Matrices-Parallel and Standard Progressive Matrices-Parallel were used to assess children's intelligence. The results showed that the mean (±standard deviation) urinary fluoride concentrations were 0.40 ± 0.27 mg/L (0.43 ± 0.23 mg/g creatinine) among participants. The prevalence of dental fluorosis was 23.67%. After extensive evaluation of potential confounders, dental fluorosis and urinary fluoride were not associated with intelligence quotient (IQ) scores or grades in the regression models. In conclusion, dental fluorosis and urinary fluoride levels were not significantly related to the IQ of schoolchildren living in areas with low drinking water fluoride.

A case study of neurodevelopmental risks from combined exposures to lead, methyl-mercury, inorganic arsenic, polychlorinated biphenyls, polybrominated diphenyl ethers and fluoride

We performed a mixture risk assessment (MRA) case study of dietary exposure to the food contaminants lead, methylmercury, inorganic arsenic (iAs), fluoride, non-dioxin-like polychlorinated biphenyls (NDL-PCBs) and polybrominated diphenyl ethers (PBDEs), all substances associated with declines in cognitive abilities measured as IQ loss. Most of these chemicals are frequently measured in human biomonitoring studies. A component-based, personalised modified reference point index (mRPI) approach, in which we expressed the exposures and potencies of our chosen substances as lead equivalent values, was applied to perform a MRA for dietary exposures. We conducted the assessment for four different age groups (toddlers, children, adolescents, and women aged 18-45 years) in nine European countries. Populations in all countries considered exceeded combined tolerable levels at median exposure levels. NDL-PCBs in fish, other seafood and dairy, lead in grains and fruits, methylmercury in fish and other seafoods, and fluoride in water contributed most to the combined exposure. We identified uncertainties for the likelihood of co-exposure, assessment group membership, endpoint-specific reference values (ESRVs) based on epidemiological (lead, methylmercury, iAs, fluoride and NDL-PCBs) and animal data (PBDE), and exposure data. Those uncertainties lead to a complex pattern of under- and overestimations, which would require probabilistic modelling based on expert knowledge elicitation for integration of the identified uncertainties into an overall uncertainty estimate. In addition, the identified uncertainties could be used to refine future MRA for cognitive decline.

Fluoride Exposure and ADHD: A Systematic Review of Epidemiological Studies

Background and objectives: Attention deficit hyperactivity disorder (ADHD) is a childhood-onset neurodevelopmental disorder characterized by two dimensions: inattentiveness and hyperactivity/impulsivity. ADHD may be the result of complex interactions between genetic, biological and environmental factors possibly including fluoride exposure. Materials and methods: A literature search was performed on 31 March 2023 in the following databases: PubMed, Embase and Web of Science. We defined the following inclusion criteria according to the PECOS statement: a healthy child and adolescent population (P), fluoride exposure of any type (E), comparison with low or null exposure (C), ADHD spectrum disorder (O), and ecological, cross-sectional, case-control and cohort studies (S). Results: We found eight eligible records corresponding to seven different studies investigating the effect of fluoride exposure on children and adolescents. One study had a cohort design and one a case-control one, while five were cross-sectional. Only three studies applied validated questionnaires for the purpose of ADHD diagnosis. As regards exposure assessment, levels of fluoride in urine and tap water were, respectively used in three and two studies, while two used both. Three studies reported a positive association with ADHD risk, all assessing exposure through fluoride levels. By using urinary fluoride, conversely, a positive correlation with inattention, internalizing symptoms, cognitive and psychosomatic problems was found in three studies, but no relation was found in the other one. Conclusions: The present review suggests that early exposure to fluoride may have neurotoxic effects on neurodevelopment affecting behavioral, cognitive and psychosomatic symptoms related to ADHD diagnosis. However, due to the heterogeneity of the studies included, current evidence does not allow to conclusively confirm that fluoride exposure is specifically linked to ADHD development.

Dietary Exposure to Toxic Elements and the Health of Young Children: Methodological Considerations and Data Needs

Concerns have been raised regarding toxic-element (arsenic, cadmium, lead, and mercury) contamination of commercially available infant foods around the world. Young children are vulnerable to the effects of toxic elements, based on higher absorption levels and potentially poorer detoxification capacities. Toxic-element exposures in early life exact high societal costs, but it is unclear how much dietary exposure to these elements contributes to adverse health outcomes. Well-designed epidemiological studies conducted in different geographical and socioeconomic contexts need to estimate dietary toxicant exposure in young children and to determine whether causal links exist between toxicants in children's diets and health outcomes. This commentary outlines the methodological considerations and data needs to advance such research.

Maternal urinary fluoride during pregnancy and birth weight and length: Results from ELEMENT cohort study

Epidemiological studies assessing prenatal fluoride exposure and anthropometry at birth are scarce, inconsistent and with methodological limitations. The aim of this study was to evaluate associations between maternal urinary fluoride (MUF) at each trimester of pregnancy and birth weight and length in 536 mother-child pairs in the Early Life Exposures in Mexico to Environmental Toxicants (ELEMENT) cohort study. MUF (mg/L) was measured using microdiffusion/fluoride-specific electrode from at least one trimester of pregnancy. Non-linear associations were assessed through segmented regression models (MUF and birth weight Z-score) and we used linear regression models for MUF and birth length Z-score. Models were adjusted for potential confounders including urinary creatinine concentrations as a covariate. Non-creatinine adjusted MUF levels at each trimester of pregnancy were 0.81, 0.86, and 0.82 mg/L, mean concentrations for first, second and third trimester, respectively. For birth weight, we identified a MUF breakpoint at 0.99, 0.68 and 0.58 mg/L, for first, second and third trimester of pregnancy, respectively. In the first trimester, an increase of 1 mg/L in MUF concentrations ≥0.99 mg/L was associated with an increase in weight Z-score at birth (β = 0.79; 95% CI: 0.10, 1.48; p = 0.02). Second trimester MUF (≥0.68 mg/L) was marginally associated with birth weight decrease (β = -0.25; 95% CI: -0.55, 0.04; p = 0.09) and third trimester MUF (≥0.58 mg/L) was significantly associated with birth weight decrease (β = -0.33; 95% CI: -0.63, -0.03; p = 0.03). We observed a linear and significant association between MUF and Z-score of length at birth only for the first trimester of pregnancy (β = 0.55; 95% CI: 0.07, 1.04; p < 0.02). Prenatal fluoride exposure was associated with birthweight z-score with different susceptibility windows. Our findings reinforce the hypothesis that maternal fluoride exposure may affect birth anthropometry.

Association between Water Fluoride Levels and Low Birth Weight: National Health and Nutrition Examination Survey (NHANES) 2013-2016

Background: Excessive fluoride consumption affects reproductive and child health. We examined the association between levels of fluoride in drinking water and birth weight, in the National Health and Nutrition Examination Survey 2013−2016, after adjusting for known risk factors Low Birth Weight (LBW) including age, smoking, and socio-demographic variables including education, food security, health care access, and health status. Methods: The study included 7147 and 6858 women with complete birth weight and water fluoride data, respectively. Linear regression models evaluated the association between water fluoride and birth weight across racial/ethnic groups. The odds of delivering an LBW infant (<2500 g) compared to an infant weighing ≥ 2500 g, as well as the odds of delivering a Very Low Birth Weight (VLBW, <1500 g) infant compared to an LBW infant were explored in separate logistic regression models. Results: Women with LBW infants were exposed to significantly higher levels of water fluoride compared to those with normal birth weight infants. Our findings suggest a significant association between excess water fluoride exposure (>0.7 ppm) and LBW weight in Hispanic women, independent of established LBW risk factors. In logistic regression models, Hispanic women exposed to increased levels of water fluoride were 1.5 times more likely to give birth to an LBW infant and 3.5 more likely to give birth to a VLBW infant. Conclusion: Taken together, these findings can inform public health education strategies that highlight water fluoride as a potential risk factor during pregnancy in Hispanic women. More research is needed to confirm these findings.

Impacts of Fluoride Neurotoxicity and Mitochondrial Dysfunction on Cognition and Mental Health: A Literature Review

This review focuses on the synthesis of current experimental and observational data regarding the effect of fluoride exposure on childhood mental health and the role of mitochondrial function as a mechanism of action. We aggregated data on the relationships between fluoride neurotoxicity, mitochondrial function, and cognitive and mental health using PubMed. Current animal and human research suggest that prenatal and perinatal fluoride exposure might have neurotoxic effects. These studies observed physical changes (fur loss and delayed reflex development in animals), intelligence loss, increased hyperactivity, and irregular moods associated with fluoride exposure. Two gaps in the literature were identified: (1) there is limited research on the mental and emotional impacts of fluoride exposure compared to research on cognitive outcomes, and (2) human studies primarily focus on prenatal and perinatal exposure, with little research conducted at other time points (e.g., adolescence). Furthermore, there is no agreed-upon mechanism for the neurotoxic effects of fluoride; however, fluoride can induce mitochondrial damage, including decreasing circulating mitochondrial DNA content, dysregulating biogenesis, and circular structure loss. Additionally, many neurodevelopmental conditions have mitochondrial underpinnings. More work is needed to elucidate the impact and timing of fluoride exposure on mental health and the role of mitochondrial function as a biological mechanism