Association Between Maternal Fluoride Exposure During Pregnancy and IQ Scores in Offspring in Canada

Controversy: The evolving science of fluoride: when new evidence doesn't conform with existing beliefs

Over the past 75 years, health authorities have declared that community water fluoridation-a practice that reaches over 400 million worldwide-is safe. Yet, studies conducted in North America examining the safety of fluoride exposure in pregnancy were nonexistent. When a Canadian study reported that higher fluoride exposure in pregnant women was associated with lower IQ scores in young children, critics attacked the methodology of the study and discounted the significance of the results. Health authorities continued to conclude that fluoride is unequivocally safe, despite four well-conducted studies over the last 3 years consistently linking fluoride exposure in pregnancy with adverse neurodevelopmental effects in offspring. We describe the challenges of conducting fluoride research and the overt cognitive biases we have witnessed in the polarized fluoride debate. The tendency to ignore new evidence that does not conform to widespread beliefs impedes the response to early warnings about fluoride as a potential developmental neurotoxin. Evolving evidence should inspire scientists and health authorities to re-evaluate claims about the safety of fluoride, especially for the fetus and infant for whom there is no benefit.

Dietary Micronutrients from Zygote to Senility: Updated Review of Minerals' Role and Orchestration in Human Nutrition throughout Life Cycle with Sex Differences

Micronutrients such as selenium, fluoride, zinc, iron, and manganese are minerals that are crucial for many body homeostatic processes supplied at low levels. The importance of these micronutrients starts early in the human life cycle and continues across its different stages. Several studies have emphasized the critical role of a well-balanced micronutrient intake. However, the majority of studies looked into or examined such issues in relation to a specific element or life stage, with the majority merely reporting the effect of either excess or deficiency. Herein, in this review, we will look in depth at the orchestration of the main element requirements across the human life cycle beginning from fertility and pregnancy, passing through infancy, childhood, adolescence, and reaching adulthood and senility, with insight on the interactions among them and underlying action mechanisms. Emphasis is given towards approaches to the role of the different minerals in the life cycle, associated symptoms for under- or overdoses, and typical management for each element, with future perspectives. The effect of sex is also discussed for each micronutrient for each life stage as literature suffice to highlight the different daily requirements and or effects.

Fluoride exposure and children's intelligence: Gene-environment interaction based on SNP-set, gene and pathway analysis, using a case-control design based on a cross-sectional study

BACKGROUND

Excessive fluoride exposure has been associated with intelligence loss, but little is known about gene-fluoride interactions on intelligence at SNP-set, gene and pathway level.

OBJECTIVES

Here we conducted a population-based study in Chinese school-aged children to estimate the associations of fluoride from internal and external exposures with intelligence as well as to explore the gene-fluoride interactions on intelligence at SNP-set, gene and neurodevelopmental pathway level.

METHODS

A total of 952 resident children aged 7 to 13 were included in the current study. The fluoride contents in drinking water, urine, hair and nail were measured using the ion-selective electrode method. LASSO Binomial regression was conducted to screen the intelligence-related SNP-set. The gene-fluoride interactions at gene and pathway levels were detected by the Adaptive Rank Truncated Product method.

RESULTS

The probability of high intelligence was inversely correlated with fluoride contents in water, urine, hair and nail (all P < 0.001). The SNP-set based on rs3788319, rs1879417, rs57377675, rs11556505 and rs7187776 was related to high intelligence (P = 0.001) alone and by interaction with water, urinary and hair fluoride (P = 0.030, 0.040, 0.010), separately. In gene level, CLU and TOMM40 interacted with hair fluoride (both P = 0.017) on intelligence. In pathway level, Alzheimer disease pathway, metabolic pathway, signal transduction pathway, sphingolipid signaling pathway and PI3K-AKT signaling pathway interacted with fluoride on intelligence in men.

CONCLUSIONS

Our study suggests that fluoride is inversely associated with intelligence. Moreover, the interactions of fluoride with mitochondrial function-related SNP-set, genes and pathways may also be involved in high intelligence loss.

Iodine Modifies the Susceptibility of Thyroid to Fluoride Exposure in School-age Children: a Cross-sectional Study in Yellow River Basin, Henan, China

Excessive fluoride exposure has detrimental effects on the thyroid gland, which may be modified by iodine. However, the role of iodine in it remains unclear. This study aims to evaluate the role of iodine in thyroid abnormalities caused by fluoride exposure in school-age children. A total of 446 children aged 7-12 years were recruited from Tongxu County, Henan province, in 2017 (ZZUIRB 2017-018). We obtained demographic information through questionnaire surveys. The concentrations of urinary fluoride (UF) and urinary iodine (UI) were determined by the ion-selective electrode method and the catalytic spectrophotometric method, respectively. The radiation immunoassay was used to determine the serum concentrations of total triiodothyronine (TT3), total thyroxine (TT4), and thyroid-stimulating hormone (TSH). The B-mode ultrasound was performed to assess thyroid volumes (Tvols). The associations between fluoride exposure and thyroid-related indicators were tested by linear regression models. We found that Tvols increased by 0.22 (95% CI: 0.14, 0.31) cm³ with each standard deviation increment of UF. Moreover, Tvols in boys were more susceptible to fluoride exposure than those in girls, and the Tvols of children with high urinary iodine are less susceptible to fluoride exposure (P for interaction < 0.05). We also observed that TT3 levels were negatively related to UF concentrations at moderate urinary iodine levels (≤ 300 μg/l). Fluoride exposure can elevate the Tvols of school-age children, especially in boys, and high levels of iodine may alleviate this effect to some extent.

Associations of low level of fluoride exposure with dental fluorosis among U.S. children and adolescents, NHANES 2015-2016

Drinking water fluoridation was a mid-twentieth century innovation based on the medical hypothesis that consuming low doses of fluoride at the teeth forming years provided protection against dental decays. Numerous studies showed that high level exposure to fluoride could cause dental and skeleton fluorosis. However, there was limited study focusing on the fluorosis effect of low levels of exposure to fluoride. Therefore, our study aimed to examine whether the low level of fluoride exposure (measured in blood plasma and household tap water) was associated with the risk of dental fluorosis based on data of the National Health and Nutrition Examination Survey (NHANES) 2015-2016. We analyzed data in 2098 children and adolescents who had Dean's Index scores, and water and plasma fluoride measures. The Dean's Index score was measured by calibrated dental examiners using the modified Dean's fluorosis classification system. Fluoride was measured in plasma and household tap water. In this study, we found that the rate of fluoride concentration in water above the recommended level of 0.7 mg/L was 25%, but the prevalence of dental fluorosis was 70%. Binary logistic regression adjusted for covariates showed that higher water fluoride concentrations (0.31-0.50, 0.51-0.70, > 0.70 compared 0.00-0.30) were associated with higher odds of dental fluorosis (OR = 1.48, 95% CI: 1.13-1.96, p = 0.005; OR = 1.92, 95% CI: 1.44-2.58, p < 0.001, and OR = 2.30, 95% CI: 1.75-3.07, p < 0.001, respectively). The pattern of regression between plasma fluoride and dental fluorosis was similar. Inclusion, our study showed that even low level of water or plasma fluoride exposure was associated with increased the risk of dental fluorosis. The safety of public health approach of drinking water fluoridation for global dental caries reduction are urgently needed further research.

Critical windows of fluoride neurotoxicity in Canadian children

BACKGROUND

Fluoride has been associated with IQ deficits during early brain development, but the period in which children are most sensitive is unknown.

OBJECTIVE

We assessed effects of fluoride on IQ scores across prenatal and postnatal exposure windows.

METHODS

We used repeated exposures from 596 mother-child pairs in the Maternal-Infant Research on Environmental Chemicals pregnancy and birth cohort. Fluoride was measured in urine (mg/L) collected from women during pregnancy and in their children between 1.9 and 4.4 years; urinary fluoride was adjusted for specific gravity. We estimated infant fluoride exposure (mg/day) using water fluoride concentration and duration of formula-feeding over the first year of life. Intelligence was assessed at 3-4 years using the Wechsler Preschool and Primary Scale of Intelligence-III. We used generalized estimating equations to examine the associations between fluoride exposures and IQ, adjusting for covariates. We report results based on standardized exposures given their varying units of measurement.

RESULTS

The association between fluoride and performance IQ (PIQ) significantly differed across prenatal, infancy, and childhood exposure windows collapsing across child sex (p = .001). The strongest association between fluoride and PIQ was during the prenatal window, B = -2.36, 95% CI: -3.63, -1.08; the association was also significant during infancy, B = -2.11, 95% CI: -3.45, -0.76, but weaker in childhood, B = -1.51, 95% CI: -2.90, -0.12. Within sex, the association between fluoride and PIQ significantly differed across the three exposure windows (boys: p = .01; girls: p = .01); among boys, the strongest association was during the prenatal window, B = -3.01, 95% CI: -4.60, -1.42, whereas among girls, the strongest association was during infancy, B = -2.71, 95% CI: -4.59, -0.83. Full-scale IQ estimates were weaker than PIQ estimates for every window. Fluoride was not significantly associated with Verbal IQ across any exposure window.

CONCLUSION

Associations between fluoride exposure and PIQ differed based on timing of exposure. The prenatal window may be critical for boys, whereas infancy may be a critical window for girls.

Contribution to the ongoing discussion on fluoride toxicity

Since the addition of fluoride to drinking water in the 1940s, there have been frequent and sometimes heated discussions regarding its benefits and risks. In a recently published review, we addressed the question if current exposure levels in Europe represent a risk to human health. This review was discussed in an editorial asking why we did not calculate benchmark doses (BMD) of fluoride neurotoxicity for humans. Here, we address the question, why it is problematic to calculate BMDs based on the currently available data. Briefly, the conclusions of the available studies are not homogeneous, reporting negative as well as positive results; moreover, the positive studies lack control of confounding factors such as the influence of well-known neurotoxicants. We also discuss the limitations of several further epidemiological studies that did not meet the inclusion criteria of our review. Finally, it is important to not only focus on epidemiological studies. Rather, risk analysis should consider all available data, including epidemiological, animal, as well as in vitro studies. Despite remaining uncertainties, the totality of evidence does not support the notion that fluoride should be considered a human developmental neurotoxicant at current exposure levels in European countries.

Urinary Fluoride Levels among Canadians with and without Community Water Fluoridation

Drinking water is a major source of dietary fluoride intake in communities with water fluoridation. We examined the association between urinary fluoride adjusted for specific gravity (UFSG) and tap water fluoride levels, by age and sex, among individuals living in Canada. Participants included 1629 individuals aged 3 to 79 years from Cycle 3 (2012-2013) of the Canadian Health Measures Survey. We used multiple linear regression to estimate unique associations of tap water fluoride levels, age, sex, ethnicity, body mass index (BMI), use of fluoride-containing dental products, smoking in the home, and tea consumption with UFSG. UFSG concentration was significantly higher among participants who received fluoridated drinking water (mean = 1.06 mg/L, standard deviation = 0.83) than among those who did not (M = 0.58 mg/L, SD = 0.47), p < 0.01. UFSG increased over adulthood (ages 19 to 79). Higher UFSG concentration was associated with being female, tea drinking, and smoking in the home. In conclusion, community water fluoridation is a major source of contemporary fluoride exposure for Canadians. Lifestyle factors including tea consumption, as well as demographic variables such as age and sex, also predict urinary fluoride level, and are therefore important factors when interpreting population-based fluoride biomonitoring data.

Chemical Aspects of Human and Environmental Overload with Fluorine

Over the last 100-120 years, due to the ever-increasing importance of fluorine-containing compounds in modern technology and daily life, the explosive development of the fluorochemical industry led to an enormous increase of emission of fluoride ions into the biosphere. This made it more and more important to understand the biological activities, metabolism, degradation, and possible environmental hazards of such substances. This comprehensive and critical review focuses on the effects of fluoride ions and organofluorine compounds (mainly pharmaceuticals and agrochemicals) on human health and the environment. To give a better overview, various connected topics are also discussed: reasons and trends of the advance of fluorine-containing pharmaceuticals and agrochemicals, metabolism of fluorinated drugs, withdrawn fluorinated drugs, natural sources of organic and inorganic fluorine compounds in the environment (including the biosphere), sources of fluoride intake, and finally biomarkers of fluoride exposure.

Understanding oral health disparities in children as a global public health issue: how dental health professionals can make a difference

Oral disease in children is an urgent public health issue worldwide. Early childhood caries (ECC) affects 600 million children globally, yet it is entirely preventable. Dental health professionals around the world need to act to improve use of measures to prevent ECC and of quality dental health care to improve oral health worldwide. The University of California/Los Angeles (UCLA) Center for Children's Oral Health hosted an interprofessional innovation forum to discuss and recommend options. We present the policy, educational, and public health-related suggestions for improving outcomes and professional collaboration and five key areas for action: (1) increase advocacy efforts, (2) support interprofessional education and practice, (3) promote oral health education and increase health literacy, (4) increase collaboration with community and school-based oral health care workers, and (5) use of technology to increase access to dental care and health information.

Community Water Fluoridation: Caveats to Implement Justice in Public Oral Health

Community water fluoridation (CWF), a long-established public health intervention, has been studied for scientific evidence from both of yea and nay standpoints. To justify CWF with scientific evidence inevitably leads to ethical justification, which raises the question of whether oral health is of individual concern or social responsibility. As dental caries is a public health problem, public health ethics should be applied to the topic instead of generic clinical ethics. From both pro- and anti-fluoridationists’ perspectives, CWF is a public health policy requiring a significant level of intervention. Thus, there needs to take further considerations for justifying CWF beyond the simple aspect of utility. For further ethical considerations on CWF, three caveats were suggested: procedural justice, social contexts, and maintenance of trust. The process to justify CWF should also be justified, not simply by majority rule but participatory decision-making with transparency and pluralistic democracy. Social contexts are to be part of the process of resolving conflicting values in public health interventions. Public trust in the dental profession and the oral healthcare system should be maintained over the considerations. This article suggests accountability for reasonableness as a framework to consider infringement by CWF for public justification of its implementation.

Dietary fluoride intake over the course of pregnancy in Mexican women

OBJECTIVE

To estimate dietary fluoride intake (F) over the course of pregnancy and the overall adjusted difference in dietary F intake by pregnancy stages and levels of compliance with dietary recommendations.

DESIGN

Secondary data analysis from a longitudinal pregnancy cohort study in a population exposed to fluoridated salt. Women were followed during the early, middle and late stages of their pregnancy (n 568). The dietary intake of recommended prenatal nutrients according to Mexican dietary guidelines and F intake (mg/d) was estimated with a validated FFQ. Data were summarised with descriptive statistics. Levels of F intake were compared with the USA's Institute of Medicine adequate intake (AI) of 3 mg/d for pregnancy. Adjusted differences in F intake by pregnancy stages and levels of compliance with recommendations were estimated using random effects models.

SETTING

Mexico City.

PARTICIPANTS

Women participating in the Early Life Exposures in Mexico to ENvironmental Toxicants (ELEMENT) project, from 2001 to 2003.

RESULTS

Median dietary F intake throughout pregnancy ranged from 0·64 (interquartile range (IQR) 0·38) in the early to 0·70 (IQR 0·42) in the middle, and 0·72 (IQR 0·44) mg/d in the late stage (0·01 mg F/kg per d). Corresponding adjusted intakes of F were 0·72 (95 % CI 0·70, 0·74), 0·76 (95 % CI 0·74, 0·77) and 0·80 (95 % CI 0·78, 0·82) mg/d. Women who were moderately and highly compliant with Mexican dietary recommendations ingested, on average, 0·04 and 0·14 mg F/d more than non-compliant women (P < 0·005).

CONCLUSIONS

Dietary F intake was below current AI, was greater with the progression of pregnancy and in women who were moderately and highly compliant with dietary recommendations.

Fluoride exposure and duration and quality of sleep in a Canadian population-based sample

BACKGROUND

Fluoride from dietary and environmental sources may concentrate in calcium-containing regions of the body such as the pineal gland. The pineal gland synthesizes melatonin, a hormone that regulates the sleep-wake cycle. We examined associations between fluoride exposure and sleep outcomes among older adolescents and adults in Canada.

METHODS

We used population-based data from Cycle 3 (2012-2013) of the Canadian Health Measures Survey. Participants were aged 16 to 79 years and 32% lived in communities supplied with fluoridated municipal water. Urinary fluoride concentrations were measured in spot samples and adjusted for specific gravity (UF_SG; n = 1303) and water fluoride concentrations were measured in tap water samples among those who reported drinking tap water (n = 1016). We used multinomial and ordered logistic regression analyses (using both unweighted and survey-weighted data) to examine associations of fluoride exposure with self-reported sleep outcomes, including sleep duration, frequency of sleep problems, and daytime sleepiness. Covariates included age, sex, ethnicity, body mass index, chronic health conditions, and household income.

RESULTS

Median (IQR) UF_SG concentration was 0.67 (0.63) mg/L. Median (IQR) water fluoride concentration was 0.58 (0.27) mg/L among participants living in communities supplied with fluoridated municipal water and 0.01 (0.06) mg/L among those living in non-fluoridated communities. A 0.5 mg/L higher water fluoride level was associated with 34% higher relative risk of reporting sleeping less than the recommended duration for age [unweighted: RRR = 1.34, 95% CI: 1.03, 1.73; p = .026]; the relative risk was higher, though less precise, using survey-weighted data [RRR = 1.96, 95% CI: 0.99, 3.87; p = .05]. UF_SG was not significantly associated with sleep duration. Water fluoride and UF_SG concentration were not significantly associated with frequency of sleep problems or daytime sleepiness.

CONCLUSIONS

Fluoride exposure may contribute to sleeping less than the recommended duration among older adolescents and adults in Canada.

The association between lithium in drinking water and neuropsychiatric outcomes: A systematic review and meta-analysis from across 2678 regions containing 113 million people

BACKGROUND

Lithium in drinking water may have significant mental health benefits. We investigated the evidence on the association between lithium concentrations in drinking water and their neuropsychiatric outcomes.

METHODS

We conducted a systematic review and meta-analysis and searched Pubmed, Embase, Web of Science, PsycINFO and CINAHL up to 19 January 2020, for peer-reviewed research examining the association between lithium concentrations in drinking water and neuropsychiatric outcomes. We used a pairwise analysis and a random effects model to meta-analyse suicide rates and psychiatric hospital admissions. We assessed for publication bias using Egger's test and Duval and Tweedie's Trim and Fill analysis.

RESULTS

Twenty-seven studies including 113 million subjects were included in this systematic review. Meta-analysis of 14 studies including 94 million people found higher lithium concentrations were associated with reduced suicide rates (r = -0.191, 95% confidence interval = [-0.287, -0.090], p < 0.001) and meta-analysis of two studies including 5 million people found higher lithium concentrations were associated with fewer hospital admissions (r = -0.413, 95% confidence interval = [-0.689, -0.031], p = 0.035). We found significant heterogeneity between studies (Q = 67.4, p < 0.001, I² = 80.7%) and the presence of publication bias (Egger's test; t value = 2.90, p = 0.013). Other included studies did not provide sufficient data to analyse other neuropsychiatric outcomes quantitatively.

CONCLUSION

Higher lithium concentrations in drinking water may be associated with reduced suicide rates and inpatient psychiatric admissions. The relationship with other neuropsychiatric outcomes and complications remains unclear. Further research is required before any public health recommendations can be made.Trial registration number: The study was registered with PROSPERO, number CRD42018090145.

Plasma and water fluoride levels and hyperuricemia among adolescents: A cross-sectional study of a nationally representative sample of the United States for 2013-2016

Exposure to excessive fluoride has been associated with a number of adverse health outcomes; however, there is a lack of evidence on the relation between fluoride exposure and serum uric acid levels, especially in human populations. The present study examined a potential relationship between fluoride exposure, measured as both plasma and water fluoride concentrations, and uric acid levels in an adolescent population. A nationally representative subsample of 1933 adolescents, aged 12-19 years, in the 2013-2016 National Health and Nutrition Examination Survey was analyzed for the association of fluoride concentrations with serum uric acid levels using multivariate general linear and logistic regression models, adjusting for potential confounders. Since uric acid levels change during development, hyperuricemia was defined in this study as over the mean plus one standard deviation for each sex and age group of adolescents. Of the study participants, 276 adolescents (weighted prevalence, 16.56%) had hyperuricemia. A significant and dose-dependent increase in prevalence of hyperuricemia was seen among the participants cross increasing quartiles of plasma fluoride (p-trend = 0.0017). After adjusting for potential confounders, we found that adolescents in the higher quartiles of plasma fluoride (≥0.32 µmol/L) and in the highest quartile of water fluoride (≥0.73 mg/L) had significantly increased odds of hyperuricemia compared with those in the lowest quartile. A 1.95-fold increased odds (95% CI: 1.37, 2.77) of hyperuricemia was also observed when analyzing plasma fluoride concentrations as continuous variable. A general linear model revealed that a 1 µmol/L increase in ln-plasma fluoride was associated with a 0.212 mg/dL (p < 0.0001) increased serum uric acid level. Furthermore, a positive relationship was observed between water and plasma fluoride concentrations (β = 0.1907; p < 0.0001). Our study demonstrates a potential relation between fluoride exposure and hyperuricemia in adolescents. Further studies are warranted to overcome the limitations of this study to examine the impact of long-term exposure to low levels of fluoride during development on hyperuricemia and its related health outcomes.

Biomarkers for Lifetime Caries-Free Status

The purpose of this study was to address the hypothesis that extreme outcomes of dental caries, such as edentulism or prematurely losing permanent teeth are associated with genetic variation in enamel-formation genes. After scanning 6206 individuals, samples of 330 were selected for this study. Tested phenotypes included patients who were edentulous by age 30, patients with missing first molars by age 30, patients with missing second molars by age 30, and caries-free patients. Fourteen single nucleotide polymorphisms were genotyped by TaqMan chemistry. The analyses of each phenotype were performed using the software PLINK with an alpha of 0.05. Nominal associations were found between rs12640848 in enamelin (p = 0.05), rs1784418 in matrix metallopeptidase 20 (p = 0.02), and rs5997096 in the tuftelin interacting protein 11 and being caries-free at the age of 60. When combining patients that were missing both first mandibular molars and missing both second mandibular molars, no associations were found. Matrix metallopeptidase 20, and tuftelin interacting protein 11 also showed trends for association with being caries-free. Genetic variation in TFIP11, MMP20, and ENAM may have a protective effect increasing the chances of individuals preserving their teeth caries-free over a lifetime.

Predictors of Plasma Fluoride Concentrations in Children and Adolescents

Despite increasing concerns about neurotoxicity of fluoride in children, sources of fluoride exposure apart from municipal water fluoridation are poorly understood. We aimed to describe the associations of demographics, drinking water characteristics, diet, and oral health behaviors with plasma fluoride concentrations in U.S. children. We used data from 3928 6–19-year-olds from the 2013–2016 National Health and Nutrition Examination Survey. We used a 24-h dietary recall to estimate recent consumption of fluoridated tap water and select foods. We estimated the associations of fluoridated tap water, time of last dental visit, use of toothpaste, and frequency of daily tooth brushing with plasma fluoride concentrations. The participants who consumed fluoridated (≥0.7 mg/L) tap water (n = 560, 16%) versus those who did not had 36% (95% CI: 22, 51) higher plasma fluoride. Children who drank black or green tea (n = 503, 13%) had 42% higher plasma fluoride concentrations (95% CI: 27, 58) than non-tea drinkers. The intake of other foods and oral health behaviors were not associated with plasma fluoride concentrations. The consumption of fluoridated tap water and tea substantially increases plasma fluoride concentrations in children. Quantifying the contribution of diet and other sources of fluoride is critical to establishing safe target levels for municipal water fluoridation.

The Association between Community Water Fluoridation and Bone Diseases: A Natural Experiment in Cheongju, Korea

The present study aimed to investigate the association between bone diseases and community water fluoridation (CWF). An ecological study with a natural experiment design was conducted in Cheongju, South Korea, from 1 January 2004 to 31 December 2013. The community water fluoridation program was implemented in Cheongju and divided into CWF and non-CWF areas. To observe adverse health effects related to bone diseases, we conducted a spatio-temporal analysis of the prevalence of hip fracture, osteoporosis, and bone cancer in residents who have lived in CWF and non-CWF areas using National Health Insurance Service data. First, we used standardized incidence ratios to estimate the disease risk. Second, the hierarchical Bayesian Poisson spatio-temporal regression model was used to investigate the association between the selected bone diseases and CWF considering space and time interaction. The method for Bayesian estimation was based on the R-integrated nested Laplace approximation (INLA). Comparing the CWF area with the non-CWF area, there was no clear evidence that exposure to CWF increased health risks at the town level in Cheongju since CWF was terminated after 2004. The posterior relative risks (RR) of hip fracture was 0.95 (95% confidence intervals 0.87, 1.05) and osteoporosis was 0.94 (0.87, 1.02). The RR in bone cancer was a little high because the sample size very small compared to the other bone diseases (RR = 1.20 (0.89, 1.61)). The relative risk of selected bone diseases (hip fractures, osteoporosis, and bone cancer) increased over time but did not increase in the CWF area compared to non-CWF areas. CWF has been used to reduce dental caries in all population groups and is known for its cost-effectiveness. These findings suggest that CWF is not associated with adverse health risks related to bone diseases. This study provides scientific evidence based on a natural experiment design. It is necessary to continue research on the well-designed epidemiological studies and develop public health prevention programs to help in make suitable polices.

Effects of Fluoride Exposure on Primary Human Melanocytes from Dark and Light Skin

Fluoride exposure has adverse effects on human health that have been studied in vitro in cell culture systems. Melanocytes are the melanin pigment-producing cells that have a significant role in the regulation of the process of melanogenesis, which provides several health benefits. Melanocytes are present in the oral cavity, skin, brain, lungs, hair, and eyes. However, to date, there has been no study on the effects of fluoride exposure on melanocytes. Hence, in the current study, we have studied the effects of sodium fluoride (NaF) exposure on neonatal human epidermal melanocytes (HEMn) derived from two different skin phototypes, lightly pigmented (LP) and darkly pigmented (DP). We have assessed the impact of a 24 h and 72 h NaF exposure on metabolic activity and membrane integrity of these cells. In addition, we have evaluated whether NaF exposure might have any impact on the physiological functions of melanocytes associated with the production of melanin, which is regulated by activity of the enzyme tyrosinase. We have also assessed if NaF exposure might induce any oxidative stress in LP and DP melanocytes, by evaluation of production of reactive oxygen species (ROS) and measurement of mitochondrial membrane potential (MMP) levels. Our results showed that HEMn-LP cells showed a higher sensitivity to NaF cytotoxicity than HEMn-DP cells, with significant cytotoxicity at concentrations >1 mM, while concentration range 0.25–1 mM were nontoxic and did not lead to oxidative stress, and also did not alter the levels of intracellular melanin or cellular tyrosinase activity, indicating that treatment up to 1 mM NaF is generally safe to melanocytes from both pigmentation phototypes.

Sex-specific neurotoxic effects of early-life exposure to fluoride: A review of the epidemiologic and animal literature

PURPOSE OF REVIEW

A growing body of evidence suggests adverse neurodevelopmental effects of early-life exposure to fluoride that may differ depending on timing of exposure and sex of the exposed. We conducted a literature search to identify the animal and human epidemiologic studies that examined sex-specific neurodevelopmental differences in response to prenatal and postnatal exposure to fluoride.

RECENT FINDINGS

Six of 138 animal studies and 15 of 106 human epidemiologic studies tested for sex-specific effects. Prenatal exposure to fluoride was associated with a male susceptibility to adverse behavioural effects in four of six animal studies and lower IQ in one of three prospective cohort studies. The body of evidence examining sex-effects associated with postnatal fluoride exposure was scarce, and many animal and cross-sectional human studies were considered to have a high risk of bias.

SUMMARY

Compared to females, male offspring appear to be more sensitive to prenatal, but not postnatal, exposure to fluoride. We discuss several sex-specific mechanisms and emphasize the need for future research.

Human exposure to fluoride from tea (Camellia sinensis) in a volcanic region-Canary Islands, Spain

Fluoride is highly present in the environment, especially in water and its derivatives. Excessive fluoride contribution to diet poses a health risk. Tea leaves accumulate fluoride and the consumption of tea (Camellia sinensis) could pose a risk to human by the excessive fluoride intake. Ninety tea samples were analyzed by potentiometry using a selective fluoride ion electrode. Mixed tea samples (2.82 ± 1.11 mg/L) and black tea samples (2.28 ± 0.79 mg/L) recorded the highest fluoride levels. The contribution of drinking water is important for increasing fluoride levels in teas. The daily consumption of two cups (250 mL per cup) of mixed and black teas prepared with La Laguna tap water does pose a health risk for children (4-8 years old) because of the high contribution percentages (74.4% and 63.6%, respectively) of the Tolerable Upper Intake Level set in 2.5 mg/day by the EFSA (European Food Safety Authority). A minor consumption in children (4-8 years old) and adults during pregnancy is advisable.

Associations between Urinary, Dietary, and Water Fluoride Concentrations among Children in Mexico and Canada

Fluoride, which may be toxic to the developing brain, is added to salt in Mexico and drinking water in Canada to prevent dental caries. We compared childhood urinary fluoride (CUF) concentrations in Mexico City and Canada to characterize patterns of fluoride exposure in these two populations. We also examined associations of CUF with dietary and water fluoride levels in Mexico City and Canada respectively. We included 561 children (ages 4–6; mean age 4.8 years) from the Programming Research in Obesity, Growth, Environment, and Social Stress (PROGRESS) cohort in Mexico City, and 645 children (ages 2–6; mean age 3.7 years) from the Maternal–Infant Research on Environmental Chemicals (MIREC) cohort in Canada. We applied Spearman correlations, T-tests, ANOVA or covariate-adjusted linear regression to examine associations of CUF (mg/L; adjusted for specific gravity) with demographics and dietary or water fluoride concentrations. We used Welch equivalence testing to compare means across cohorts. Mean (SD) CUF was equivalent (t = 4.26, p < 0.001) in PROGRESS: 0.74 (0.42) and fluoridated Canadian communities: 0.66 (0.47), but lower in non-fluoridated Canadian communities: 0.42 (0.31) (t = −6.37, p < 0.001). Water fluoride concentrations were significantly associated with CUF after covariate adjustment for age and sex in MIREC (B = 0.44, 95% CI: 0.30, 0.59, p < 0.001). In contrast, daily food and beverage fluoride intake was not associated with CUF in PROGRESS (p = 0.82). We found that CUF levels are comparable among children in Mexico City and fluoridated Canadian communities, despite distinct sources of exposure. Community water fluoridation is a major source of fluoride exposure for Canadian children.

Fluoride exposure and intelligence in school-age children: evidence from different windows of exposure susceptibility

Background

The intellectual loss induced by fluoride exposure has been extensively studied, but the association between fluoride exposure in different susceptibility windows and children’s intelligence is rarely reported. Hence, we conducted a cross-sectional study to explore the association between fluoride exposure in prenatal and childhood periods and intelligence quotient (IQ).

Methods

We recruited 633 local children aged 7–13 years old randomly from four primary schools in Kaifeng, China in 2017. The children were divided into four groups, of which included: control group (CG, n = 228), only prenatal excessive fluoride exposure group (PFG, n = 107), only childhood excessive fluoride exposure group (CFG, n = 157), both prenatal and childhood excessive fluoride exposure group (BFG, n = 141). The concentrations of urinary fluoride (UF) and urinary creatinine (UCr) were determined by fluoride ion-selective electrode assay and a creatinine assay kit (picric acid method), respectively. The concentration of UCr-adjusted urinary fluoride (CUF) was calculated. IQ score was assessed using the second revision of the Combined Raven’s Test-The Rural in China (CRT-RC2). Threshold and saturation effects analysis, multiple linear regression analysis and logistic regression analysis were conducted to analyze the association between fluoride exposure and IQ.

Results

The mean IQ score in PFG was respectively lower than those in CG, CFG and BFG (P < 0.05). The odds of developing excellent intelligence among children in PFG decreased by 51.1% compared with children in CG (OR = 0.489, 95% CI: 0.279, 0.858). For all the children, CUF concentration of ≥1.7 mg/L was negatively associated with IQ scores (β = − 4.965, 95% CI: − 9.198, − 0.732, P = 0.022). In children without prenatal fluoride exposure, every 1.0 mg/L increment in the CUF concentration of ≥2.1 mg/L was related to a reduction of 11.4 points in children’s IQ scores (95% CI: − 19.2, − 3.5, P = 0.005).

Conclusions

Prenatal and childhood excessive fluoride exposures may impair the intelligence development of school children. Furthermore, children with prenatal fluoride exposure had lower IQ scores than children who were not prenatally exposed; therefore the reduction of IQ scores at higher levels of fluoride exposure in childhood does not become that evident.

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

As a safe exposure level for fluoride in pregnancy has not been established, we used data from two prospective studies for benchmark dose modeling. We included mother-child pairs from the Early Life Exposures in Mexico to Environmental Toxicants (ELEMENT) cohort in Mexico and the Maternal-Infant Research on Environmental Chemicals (MIREC) cohort in Canada. Children were assessed for IQ at age 4 (n=211) and between 6 and 12 years (n=287) in the ELEMENT cohort and between ages 3 and 4 years (n=512) in the MIREC cohort. We calculated covariate-adjusted regression coefficients and their standard errors to explore the concentration-effect function for maternal urinary fluoride with children's IQ, including possible sex-dependence. Assuming a benchmark response of 1 IQ point, we derived benchmark concentrations (BMCs) of maternal urinary fluoride and benchmark concentration levels (BMCLs). No deviation from linearity was detected from the results of the two studies. Using a linear slope, the BMC for maternal urinary fluoride associated with a 1-point decrease in IQ scores of preschool-aged boys and girls was 0.29 mg/L (BMCL, 0.18 mg/L). The BMC was 0.30 mg/L (BMCL, 0.19 mg/L) when pooling the IQ scores from the older ELEMENT children and the MIREC cohort. Boys showed slightly lower BMC values compared with girls. Relying on two prospective studies, maternal urine-fluoride exposure at levels commonly occurring in the general population, the joint data showed BMCL results about 0.2 mg/L. These results can be used to guide decisions on preventing excess fluoride exposure in vulnerable populations.

Mechanisms of Fluoride Toxicity: From Enzymes to Underlying Integrative Networks

Fluoride has been employed in laboratory investigations since the early 20th century. These studies opened the understanding of fluoride interventions to fundamental biological processes. Millions of people living in endemic fluorosis areas suffer from various pathological disturbances. The practice of community water fluoridation used prophylactically against dental caries increased concern of adverse fluoride effects. We assessed the publications on fluoride toxicity until June 2020. We present evidence that fluoride is an enzymatic poison, inducing oxidative stress, hormonal disruptions, and neurotoxicity. Fluoride in synergy with aluminum acts as a false signal in G protein cascades of hormonal and neuronal regulations in much lower concentrations than fluoride acting alone. Our review shows the impact of fluoride on human health. We suggest focusing the research on fluoride toxicity to the underlying integrative networks. Ignorance of the pluripotent toxic effects of fluoride might contribute to unexpected epidemics in the future.

Effects of Fluoride Long-Term Exposure over the Cerebellum: Global Proteomic Profile, Oxidative Biochemistry, Cell Density, and Motor Behavior Evaluation

Although the literature does not provide evidence of health risks from exposure to fluoride (F) in therapeutic doses, questions remain about the effects of long-term and high-dose use on the function of the central nervous system. The objective of this study was to investigate the effect of long-term exposure to F at levels similar to those found in areas of artificial water fluoridation and in areas of endemic fluorosis on biochemical, proteomic, cell density, and functional parameters associated with the cerebellum. For this, mice were exposed to water containing 10 mg F/L or 50 mg F/L (as sodium fluoride) for 60 days. After the exposure period, the animals were submitted to motor tests and the cerebellum was evaluated for fluoride levels, antioxidant capacity against peroxyl radicals (ACAP), lipid peroxidation (MDA), and nitrite levels (NO). The proteomic profile and morphological integrity were also evaluated. The results showed that the 10 mg F/L dose was able to decrease the ACAP levels, and the animals exposed to 50 mg F/L presented lower levels of ACAP and higher levels of MDA and NO. The cerebellar proteomic profile in both groups was modulated, highlighting proteins related to the antioxidant system, energy production, and cell death, however no neuronal density change in cerebellum was observed. Functionally, the horizontal exploratory activity of both exposed groups was impaired, while only the 50 mg F/L group showed significant changes in postural stability. No motor coordination and balance impairments were observed in both groups. Our results suggest that fluoride may impair the cerebellar oxidative biochemistry, which is associated with the proteomic modulation and, although no morphological impairment was observed, only the highest concentration of fluoride was able to impair some cerebellar motor functions.

Association Between Community Water Fluoridation and Severe Dental Caries Experience in 4-Year-Old New Zealand Children

IMPORTANCE

Robust contemporary epidemiologic evidence for the population-wide efficacy of reticulated community water fluoridation is required.

OBJECTIVE

To evaluate whether community water fluoridation is associated with the national rates of severe caries among 4-year-old children in New Zealand after accounting for key sociodemographic characteristics.

DESIGN, SETTING, AND PARTICIPANTS

This was a near whole population-level, natural, geospatial cross-sectional study of 4-year-old children who had a health and development assessment as part of the nationwide B4 School Check screening program conducted in New Zealand between July 1, 2010, and June 30, 2016. The extracted database included 391 677 children. However, geospatial information was missing for 18 558 children, another 32 939 children were unable to be geospatially matched, 5551 children resided in areas with changing fluoridation status, and 58 786 children had no oral health screen recorded, leaving 275 843 (70.4%) eligible children. Data were released in August 2019; statistical analysis was performed from September 2019 to December 2019.

EXPOSURES

Community water fluoridation status from 2011 through 2016.

MAIN OUTCOMES AND MEASURES

Severe caries experience derived from the "lift the lip" oral health screening. Analyses were adjusted for age, sex, ethnicity, area-level deprivation, and residential location differences. Multilevel mixed-effects logistic regression models were used. Sensitivity analyses based on multiple imputed data were undertaken to measure any differential influence of missing data.

RESULTS

In the eligible sample of 275 843 children, the median age was 4.3 years (interquartile range, 4.1-4.6 years), 141 451 children (51.3%) were boys, and 153 670 children (55.7%) resided within fluoridated areas. Severe caries were identified for 24 226 children (15.8%) in fluoridated and 17 135 children (14.0%) in unfluoridated areas, yielding an unadjusted odds ratio of 0.93 (95% CI, 0.90-0.95). However, in the adjusted analyses, children residing in areas without fluoridation had higher odds of severe caries compared with those within fluoridated areas (odds ratio, 1.21; 95% CI, 1.17-1.24). The population attributional fraction associated with unfluoridated community water was 5.6% (95% CI, 4.7%-6.6%) in a complete case analysis.

CONCLUSIONS AND RELEVANCE

This study finds that community water fluoridation continues to be associated with reduced prevalence of severe caries in the primary dentition of New Zealand's 4-year-old children.

Chronic exposure to environmentally relevant concentration of fluoride alters Ogg1 and Rad51 expressions in mice: Involvement of epigenetic regulation

Chronic exposure to fluoride (F) beyond the permissible limit (1.5 ppm) is known to cause detrimental health effects by induction of oxidative stress-mediated DNA damage overpowering the DNA repair machinery. In the present study, we assessed F induced oxidative stress through monitoring biochemical parameters and looked into the effect of chronic F exposure on two crucial DNA repair genes Ogg1 and Rad51 having important role against ROS induced DNA damages. To address this issue, we exposed Swiss albino mice to an environmentally relevant concentration of fluoride (15 ppm NaF) for 8 months. Results revealed histoarchitectural damages in liver, brain, kidney and spleen. Depletion of GSH, increase in lipid peroxidation and catalase activity in liver and brain confirmed the generation of oxidative stress. qRT-PCR result showed that expressions of Ogg1 and Rad51 were altered after F exposure in the affected organs. Promoter hypermethylation was associated with the downregulation of Rad51. F-induced DNA damage and the compromised DNA repair machinery triggered intrinsic pathway of apoptosis in liver and brain. The present study indicates the possible association of epigenetic regulation with F induced neurotoxicity.

Removal of fluoride from water using activated carbon fibres modified with zirconium by a drop-coating method

Metal-modified carbon materials have been widely used for fluoride removal, but the traditional impregnation by soaking method suffers from low loading of metals and substantial use of chemicals. This study proposed a new approach to prepare zirconium modified activated carbon fibres (Zr-ACF) by a drop-coating method. Using the same amount of chemicals, the drop-coating method yielded a 5.5 times higher fluoride adsorption capacity than the soaking method due to more effective loading of Zr(IV) onto ACF. The effects of various preparation conditions, including the addition of a complexing agent (oxalic acid) and Zr/ACF mass ratio (0.2-1), were investigated. Zr-ACF prepared by drop-coating was characterised by SEM and BET, and the functional groups involved in the anchoring of Zr(IV) on ACF and the adsorption of fluoride onto Zr-ACF were identified by FTIR and XPS. Adsorption experiments at pH between 3 and 11 revealed that ion exchange and electrostatic attraction were the main adsorption mechanisms at different pH levels. Co-existing anions such as CO₃^2-, HCO₃^- and Cl^- had an insignificant negative impact (<5%) on fluoride adsorption capacity while SO₄^2- decreased fluoride adsorption capacity by 11.5%. The adsorption kinetics followed the pseudo-second-order model. The adsorption isotherms followed the Langmuir isotherm model with a maximum fluoride adsorption capacity of 28.50 mg/L at 25 °C, which was higher than other carbon-based materials in the literature. The remarkable improvement of adsorption capacity and reduced chemical consumption demonstrate that Zr-ACF prepared by drop-coating is a promising adsorbent for fluoride removal.

A Cross-Sectional Analysis of Community Water Fluoridation and Prevalence of Pediatric Dental Surgery Among Medicaid Enrollees

IMPORTANCE

Dental surgery under general anesthesia (DGA) is an ineffective, costly treatment for caries. Interventions to reduce the need for DGA are challenging because children's parents may not seek care until surgery is required. Community water fluoridation (CWF) effectively prevents early childhood caries, but its effectiveness in reducing severe early childhood caries is unknown.

OBJECTIVE

To determine whether access to CWF is associated with the prevalence of DGA.

DESIGN, SETTING, AND PARTICIPANTS

This is a cross-sectional analysis of Medicaid claims data from 2011 to 2012. Deidentified data were derived from Medicaid claims and enrollee files for Massachusetts, Texas, Connecticut, Illinois, and Florida for children aged 9 years and younger enrolled in either a fee-for-service or managed care plan through their state's Medicaid program. Linear regression models tested for associations between CWF and covariates. Multivariable linear regression models tested for associations between CWF and outcomes. Regression models included clustered SEs at the county level. Data analysis was performed from December 2018 to March 2020.

EXPOSURES

Access to CWF was determined by estimating the proportion of a county's total population that had access to a fluoridated public water system.

MAIN OUTCOMES AND MEASURES

The main outcome was county-level DGA prevalence. Other outcomes were caries-related visit prevalence and patient quality indicators (asthma and diabetes). Covariates included county-level demographic, socioeconomic, and dental practitioner variables.

RESULTS

A total of 436 counties within 5 states per year (872 county-year observations), were included in the analysis. Adjusted analysis revealed that a 10% increase in the proportion of county's population access to CWF was associated with lower caries-related visit prevalence (-0.45 percentage points; 95% CI, -0.59 to -0.31 percentage points; P < .001). Increasing CWF access in 10% increments was associated with decreased DGA prevalence in unadjusted analysis (-0.39 percentage points; 95% CI, -0.67 to -0.12 percentage points; P = .006) but not in adjusted analysis (-0.23 percentage points; 95% CI, -0.49 to 0.02 percentage points; P = .07). Increasing the proportion of county's access to CWF by 10% was not associated with the prevalence of asthma-related exacerbations (-0.02 percentage points; 95% CI, -0.10 to 0.05 percentage points; P = .53) or diabetes-related exacerbations (-0.0003 percentage points; 95% CI, -0.0014 to 0.0009 percentage points; P = .66).

CONCLUSIONS AND RELEVANCE

This study extends our understanding of CWF's benefits for children's oral health. Specifically, these findings suggest that increasing a population's access to CWF's is associated with decreased caries-related visits and may also be associated with use of dental surgical services within high-risk populations.

Effect of hesperidin on fluoride-induced neurobehavioral and biochemical changes in rats

Fluoride is the second largest contaminant of drinking water. Fluoride toxicity is a major concern in the endemic areas where a high amount of fluoride is present in ground water. Oxidative stress has been proposed to be one of the mechanisms of fluoride-induced toxicity. Antioxidant-rich food has been found to alleviate fluoride-induced toxicity. Therefore, in this study, we have examined the effect of hesperidin on fluoride-induced neurobehavioral changes in rats. In the current study, male Sprague-Dawley rats were exposed to sodium fluoride through drinking water (120 ppm). Hesperidin (200 mg kg^-1  d^-1 ; per os) was administered either alone or in combination with fluoride-containing drinking water. Bisphinol A diglycidyl ether (BADGE) was used as peroxisome proliferator-activated receptor-γ (PPAR-γ) antagonist and was administered (10 mg kg^-1  d^-1 ; intraperitoneal injection) with/without hesperidin along with fluoride-containing drinking water. The behavioral changes in the animals were assessed by analyzing rotarod test, novel object recognition test, and forced swim test (FST). After 8 weeks, animals were killed to isolate blood and brain for monitoring biochemical changes. The 8-week exposure of fluoride resulted in motor impairment as observed with reduced fall time in rotarod test, memory impairment as observed with reduced preference index in novel object recognition test, and depression-like behavior as observed with reduced mobility index in the FST. Treatment with hesperidin improved neurobehavioral impairment along with restoration in brain biochemical changes (ie, acetylcholinesterase activity and antioxidant and oxidative stress parameters). The protective effect of hesperidin was reversed by coadministration of BADGE. The neuroprotective effect of hesperidin appears to be contributed through PPAR-γ receptor.

Parental acceptance of silver diammine fluoride in children with autism spectrum disorder

BACKGROUND

Parents of children with autism spectrum disorder (ASD) may have concerns with fluoride/silver content in silver diammine fluoride (SDF).

AIM

To compare parental acceptance of SDF and dental fear between children with and without ASD.

DESIGN

Three hundred parents were enrolled. Demographics, dental history, and dental fear were recorded. Subjects viewed an educational video and completed survey about SDF acceptance including the following: (a) overall acceptance, (b) aesthetic concerns by tooth location, (c) fluoride/silver concerns, and (d) its use as a general anaesthesia (GA) alternative. Descriptive, bivariate, and multivariate analyses were used.

RESULTS

Significantly, more children with ASD had dental fear (ASD: 56% vs neurotypical: 26%). No differences in acceptance existed between the two groups overall or with respect to aesthetics, fluoride/silver content, or as an alternative to GA. Overall acceptance is >60%. Regardless of group, parents of older children were less likely to accept SDF as an alternative to GA (OR = 0.67 [95% CI: 0.50-0.90]).

CONCLUSION

Parents of children with ASD had similar acceptance of SDF use compared to parents of neurotypical children. Children with ASD had higher levels of dental fear. Parents of younger children are more likely to accept SDF as an alternative to GA in both groups.

Assessment of fluoride levels during pregnancy and its association with early adverse pregnancy outcomes

Background and Aim:

There is sparse data available on human subjects regarding the affect of excessive fluoride exposures on pregnancy. The aim of this study was to examine the association between elevated urinary fluoride levels during early pregnancy and maternal anemia and adverse fetal outcome.

Patients and Methods:

We enrolled 600 pregnant patients with gestational age less than 20 weeks and with a high urinary fluoride levels(>1 mg/L).We also documented the fluoride levels in the tap water and ground water samples collected from the areas where these women resided during pregnancy. These patients were also evaluated for hemoglobin levels and detailed fetal examination by ultrasound. Data was assessed by SSPS version 16.0 software and P < 0.05 was considered to be significant.

Results:

Urinary fluoride averaged 2.65 mg/L and ranged from 1.0 to 4.3 mg/L while all the water samples revealed fluoride levels greater than WHO prescribed the limit of 1.5 mg/L. A total of 402 patients (67%) were found to be anemic with hemoglobin levels ranging from 6.2 to 11.9 g/dl (9.28 ± 1.29). Eighty one patients (13.5%) had adverse fetal outcomes that comprised abortions, congenital abnormalities, and intrauterine deaths (IUDs). There was a negative correlation between urinary fluoride and hemoglobin levels (P = 0.031, r= -0.59) and females with elevated urinary fluoride levels were found to have a strong association with the pregnancy complications, i.e., anemia, miscarriage, abortion, and still birth (χ² = 9.23, P < 0.05).

Conclusions:

Excess fluoride exposures can have deleterious effects on the expecting mother and fetus and is associated with adverse pregnancy outcomes.

One-pot synthesis of Cr(III)-incorporated Zr(IV) oxide for fluoride remediation: a lab to field performance evaluation study

A low-cost Cr(III)-incorporated Zr(IV) bimetallic oxide (CZ) was synthesized by simple chemical precipitation method for removal of fluoride from contaminated water. The physicochemical properties of CZ before and after fluoride removal were established with several instrumental techniques such as TEM with elemental mapping, SEM with EDX, XRD, IR, XPS, zeta potential measurement, etc. Batch adsorption technique were carried out to understand the factors affecting fluoride adsorption, such as effects of initial pH, adsorbent dose, co-occurring ions, contact time, and temperature. The maximum adsorption capacity observed at pH between 5 and 7. The fluoride adsorption processes on CZ obeyed the pseudo-second-order rate equations and both Freundlich and DR isotherm models. The maximum adsorption capacity of 90.67 mg g^-1 was obtained. The thermodynamic parameters ΔH⁰ (positive), ΔS⁰ (positive), and ΔG⁰ (negative) indicating the fluoride sorption system was endothermic, spontaneous, and feasible. The CZ also successfully used as fluoride adsorbent for real field contaminated water collected from the Machatora district, Bankura, West Bengal, India. Graphical abstract Schematic representation of CZ synthesis and its application for lab as well as field water purification purpose.

Histone acetyltransferase promotes fluoride toxicity in LS8 cells

Previously we demonstrated that fluoride increased acetylated-p53 (Ac-p53) in LS8 cells that are derived from mouse enamel organ epithelia and in rodent ameloblasts. However, how p53 is acetylated by fluoride and how the p53 upstream molecular pathway responds to fluoride is not well characterized. Here we demonstrate that fluoride activates histone acetyltransferases (HATs) including CBP, p300, PCAF and Tip60 to acetylate p53. HAT activity is regulated by post-translational modifications such as acetylation and phosphorylation. HAT proteins and their post-translational modifications (p300, Acetyl-p300, CBP, Acetyl-CBP, Tip60 and phospho-Tip60) were analyzed by Western blots. p53-HAT binding was detected by co-immunoprecipitation (co-IP). Cell growth inhibition was analyzed by MTT assays. LS8 cells were treated with NaF with/without HAT inhibitors MG149 (Tip60 inhibitor) and Anacardic Acid (AA; inhibits p300/CBP and PCAF). MG149 or AA was added 1 h prior to NaF treatment. Co-IP results showed that NaF increased p53-CBP binding and p53-PCAF binding. NaF increased active Acetyl-p300, Acetyl-CBP and phospho-Tip60 levels, suggesting that fluoride activates these HATs. Fluoride-induced phospho-Tip60 was decreased by MG149. MG149 or AA treatment reversed fluoride-induced cell growth inhibition at 24 h. MG149 or AA treatment decreased fluoride-induced p53 acetylation to inhibit caspase-3 cleavage, DNA damage marker γH2AX expression and cytochrome-c release into the cytosol. These results suggest that acetylation of p53 by HATs contributes, at least in part, to fluoride-induced toxicity in LS8 cells via cell growth inhibition, apoptosis, DNA damage and mitochondrial damage. Modulation of HAT activity may, therefore, be a potential therapeutic target to mitigate fluoride toxicity in ameloblasts.

Toxicity of fluoride: critical evaluation of evidence for human developmental neurotoxicity in epidemiological studies, animal experiments and in vitro analyses

Recently, epidemiological studies have suggested that fluoride is a human developmental neurotoxicant that reduces measures of intelligence in children, placing it into the same category as toxic metals (lead, methylmercury, arsenic) and polychlorinated biphenyls. If true, this assessment would be highly relevant considering the widespread fluoridation of drinking water and the worldwide use of fluoride in oral hygiene products such as toothpaste. To gain a deeper understanding of these assertions, we reviewed the levels of human exposure, as well as results from animal experiments, particularly focusing on developmental toxicity, and the molecular mechanisms by which fluoride can cause adverse effects. Moreover, in vitro studies investigating fluoride in neuronal cells and precursor/stem cells were analyzed, and 23 epidemiological studies published since 2012 were considered. The results show that the margin of exposure (MoE) between no observed adverse effect levels (NOAELs) in animal studies and the current adequate intake (AI) of fluoride (50 µg/kg b.w./day) in humans ranges between 50 and 210, depending on the specific animal experiment used as reference. Even for unusually high fluoride exposure levels, an MoE of at least ten was obtained. Furthermore, concentrations of fluoride in human plasma are much lower than fluoride concentrations, causing effects in cell cultures. In contrast, 21 of 23 recent epidemiological studies report an association between high fluoride exposure and reduced intelligence. The discrepancy between experimental and epidemiological evidence may be reconciled with deficiencies inherent in most of these epidemiological studies on a putative association between fluoride and intelligence, especially with respect to adequate consideration of potential confounding factors, e.g., socioeconomic status, residence, breast feeding, low birth weight, maternal intelligence, and exposure to other neurotoxic chemicals. In conclusion, based on the totality of currently available scientific evidence, the present review does not support the presumption that fluoride should be assessed as a human developmental neurotoxicant at the current exposure levels in Europe.

Maternal and fetal exposures to fluoride during mid-gestation among pregnant women in northern California

BACKGROUND

Previous studies have shown a correlation between fluoride concentrations in urine and community water fluoride concentrations. However, there are no studies of the relationship between community water fluoridation, urine, serum, and amniotic fluid fluoride concentrations in pregnant women in the US. The aim of this study was to determine the relationship between maternal urine fluoride (MUF), maternal urine fluoride adjusted for specific gravity (MUF_SG), maternal serum fluoride (MSF), amniotic fluid fluoride (AFF) concentrations during pregnancy, and community water fluoridation in Northern California.

METHODS

Archived samples of urine, serum and amniotic fluid collected from second trimester pregnant women in Northern California from 47 different communities in Northern California and one from Montana (n = 48), were analyzed for fluoride using an ion specific electrode following acid microdiffusion. Women's addresses were matched to publicly reported water fluoride concentrations. We examined whether fluoride concentrations in biospecimens differed by fluoridation status of the community water, and determined the association between water fluoride concentrations and biospecimen fluoride concentrations using linear regression models adjusted for maternal age, smoking, Body Mass Index (BMI), race/ethnicity, and gestational age at sample collection.

RESULTS

Fluoride concentrations in the community water supplies ranged from 0.02 to 1.00 mg/L. MUF, MSF , and AFF concentrations were significantly higher in pregnant women living in communities adhering to the U.S. recommended water fluoride concentration (0.7 mg/L), as compared with communities with less than 0.7 mg/L fluoride in drinking water. When adjusted for maternal age, smoking status, BMI, race/ethnicity, and gestational age at sample collection, a 0.1 mg/L increase in community water fluoride concentration was positively associated with higher concentrations of MUF (B = 0.052, 95% CI:0.019,0.085), MUF_SG (B = 0.028, 95% CI: -0.006, 0.062), MSF (B = 0.001, 95% CI: 0.000, 0.003) and AFF (B = 0.001, 95% CI: 0.000, 0.002).

CONCLUSIONS

We found universal exposure to fluoride in pregnant women and to the fetus via the amniotic fluid. Fluoride concentrations in urine, serum, and amniotic fluid from women were positively correlated to public records of community water fluoridation. Community water fluoridation remains a major source of fluoride exposure for pregnant women living in Northern California.

Principles of fluoride toxicity and the cellular response: a review

Fluoride is ubiquitously present throughout the world. It is released from minerals, magmatic gas, and industrial processing, and travels in the atmosphere and water. Exposure to low concentrations of fluoride increases overall oral health. Consequently, many countries add fluoride to their public water supply at 0.7-1.5 ppm. Exposure to high concentrations of fluoride, such as in a laboratory setting often exceeding 100 ppm, results in a wide array of toxicity phenotypes. This includes oxidative stress, organelle damage, and apoptosis in single cells, and skeletal and soft tissue damage in multicellular organisms. The mechanism of fluoride toxicity can be broadly attributed to four mechanisms: inhibition of proteins, organelle disruption, altered pH, and electrolyte imbalance. Recently, there has been renewed concern in the public sector as to whether fluoride is safe at the current exposure levels. In this review, we will focus on the impact of fluoride at the chemical, cellular, and multisystem level, as well as how organisms defend against fluoride. We also address public concerns about fluoride toxicity, including whether fluoride has a significant effect on neurodegeneration, diabetes, and the endocrine system.

Fluoride levels in supply water from a volcanic area in the Macaronesia region

Fluoride is a widely distributed ion in the environment and, consequently, in water as well. High levels of fluoride in waters can be found in the Canary Islands because of their volcanic origin. Due to the risk and detrimental effects associated with a high fluoride intake, the content of this ion has been potentiometrically determined in 256 supply water samples from the islands of Tenerife, El Hierro, and La Palma, using a fluoride selective ion electrode. Fluoride mean concentration found on Tenerife is 4.22 mg/L, exceeding the parametric value of 1.5 mg/L set out in Spanish legislation. The consumption of 2 L of water from the studied municipalities of Tenerife would mean there is an excessive fluoride intake. The consumption of this water poses a serious risk to health. It is necessary to take action aimed at reducing the level of fluoride in the north of the island of Tenerife.

[Oral cavity as a target and a marker of environmental exposures: developmental dental defects]

The oral cavity is one of the main route for environmental contaminations associated to many chronic diseases (cancers, fertility and behavior disorders for example) via alimentation, medications and respiration. These environmental factors including, among others, endocrine disruptors and excessive fluoride can disrupt dental development and thus generate irreversible enamel defects. These defects are then treated with materials that may release molecules capable of generating these defects, leading to a vicious circle, particularly in pregnant women and young children. The present paper aims to review the state of knowledge, questions and controversies on common environmental factors in contact with the oral cavity. It also reviews their mechanisms of action and the mediators involved in enamel pathologies associated with environmental conditions. Dental tissues can not only be targeted by environmental factors but can also serve as early and easily accessible markers of exposure to these agents. Understanding and characterizing the environmental impact in the oral cavity will help to prevent multiple diseases, oral and distant, whose link with oral homeostasis is just being explored.