Effect of fluoride exposure on the intelligence of school children in Madhya Pradesh, India

Community Water Fluoridation in Focus: A Comprehensive Look at Fluoridation Levels across America

Objective: This study reports on the number and percentage of community water systems (CWSs) meeting fluoride concentration standards set by the U.S. Department of Health and Human Services (DHHS). The study also explored changes in the population exposed to optimally fluoridated water in these systems between 2006 and 2020. Methods: This study analyzed U.S. Centers for Disease Control and Prevention data from 2006 to 2020, tabulating state-specific CWS fluoridation rates, ranking them, and calculating the percent change. Results: In 2020, 72.7% of the US population received CWS water, with 62.9% of those individuals served by a CWS system meeting DHHS fluoridation standards. This compares to 69.2% receiving CWS water in 2006 and 74.6% in 2012. The overall change in those receiving fluoridated water was 1.4%, from 61.5% in 2006 to 62.9% in 2020. State-specific percentages ranged from 8.5% in Hawaii to 100% in Washington DC in 2020 (median: 76.4%). Conclusions: Although endorsed by the American Dental Association, the percentage of individuals receiving fluoridated water did not increase substantially from 2006 to 2020, indicating that there has not been much progress toward meeting the Healthy People 2030 goal that 77.1% of Americans receive water with enough fluoride to prevent tooth decay.

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.

Fluoride exposure and cognitive neurodevelopment: Systematic review and dose-response meta-analysis

Many uncertainties still surround the possible harmful effect of fluoride exposure on cognitive neurodevelopment in children. The aim of this systematic review and meta-analysis was to characterize this relation through a dose-response approach, by comparing the intelligence quotient (IQ) scores in the highest versus the lowest fluoride exposure category with a random-effects model, within a one-stage dose-response meta-analysis based on a cubic spline random-effects model. Out of 1996 potentially relevant literature records, 33 studies were eligible for this review, 30 of which were also suitable for meta-analysis. The summary mean difference of IQ score, comparing highest versus lowest fluoride categories and considering all types of exposure, was -4.68 (95% confidence interval-CI -6.45; -2.92), with a value of -5.60 (95% CI -7.76; -3.44) for drinking water fluoride and -3.84 (95% CI -7.93; 0.24) for urinary fluoride. Dose-response analysis showed a substantially linear IQ decrease for increasing water fluoride above 1 mg/L, with -3.05 (95% CI -4.06; -2.04) IQ points per 1 mg/L up to 2 mg/L, becoming steeper above such level. A weaker and substantially linear decrease of -2.15 (95% CI -4.48; 0.18) IQ points with increasing urinary fluoride emerged above 0.28 mg/L (approximately reflecting a water fluoride content of 0.7 mg/L). The inverse association between fluoride exposure and IQ was particularly strong in the studies at high risk of bias, while no adverse effect emerged in the only study judged at low risk of bias. Overall, most studies suggested an adverse effect of fluoride exposure on children's IQ, starting at low levels of exposure. However, a major role of residual confounding could not be ruled out, thus indicating the need of additional prospective studies at low risk of bias to conclusively assess the relation between fluoride exposure and cognitive neurodevelopment.

The Relationship between Fluoride Exposure and Cognitive Outcomes from Gestation to Adulthood-A Systematic Review

Chronic exposure to high levels of fluoride may cause health concerns, including in cognitive function. This study reviewed the evidence on the association between fluoride exposure and cognitive outcomes in children from gestation up to 18 years old. A literature search was conducted for studies on pregnant women and children below 18, exposed to any source of fluoride, and assessed with a validated cognitive tool. The data were analyzed using a systematic narrative synthesis approach and by subgroup: study design, age of participants, levels of fluoride exposure and methodological quality. Our search retrieved 15,072 articles, of which 46 met the inclusion criteria. Only 6 of the studies had a longitudinal design; the remainder were cross-sectional. The levels of fluoride exposure were ≥2 mg/L in 27 studies and <2 mg/L in 13 studies; 6 studies did not report levels of fluoride exposure. Only 1 of 5 studies graded as excellent quality showed a negative association between fluoride exposure and cognitive outcomes, whereas 30 of 34 poor and fair quality studies reported a negative association. The overall evidence from this review suggests that high fluoride exposure might be associated with negative cognitive outcomes in children. However, more longitudinal studies with high methodological quality are needed on this topic.

Remediation of Soils Contaminated by Fluoride Using a Fermentation Product of Seaweed (Eucheuma cottonii)

This study investigated the efficacy of fermented seaweed (Eucheuma cottonii) on the remediation of fluoride-contaminated soil. The soil was amended with either 1.25, 3.0, or 5.0% (w/w) fermented seaweed (FSW), parallel with the controls (0%). The amendment improved the physicochemical properties of the soil particularly pH regulated from strong alkaline (9.3) to neutral (7.0) which is essential for germination, crop growth, and yield. The amount of water soluble-fluoride (Ws-F) dropped from 81.7 ± 3.1 mg/kg to 42.7 ± 2.4, 33.7 ± 1.2, 19.6 ± 0.9, and 12 ± 1.3 mg/kg following 0, 1.25, 3, and 5% amendment dosage, respectively. Most of the Ws-F was converted into exchangeable fluoride (Ex-F) and to fluoride-bound to iron and manganese (Fe/Mn-F). Furthermore, the amendment also enhanced microbial mass and diversity in the soil. The FSW contains organic acids which participate in ionic bonding with the multivalent cations in the soil. The formed compound participates in ion exchange with clay or with anionic adsorption to positively charged clay sites at the edges. This interaction is further essential for enhancing the fluoride holding capacity of the soil. The use of seaweed reduced the bioavailability of fluoride in the agricultural soils and had positive effects on promoting soil fertility. However, further studies to observe its effects on crop performance is of significance.

Groundwater fluoride across the Punjab plains of Pakistan and India: Distribution and underlying mechanisms

Chronic exposure from drinking well-water with naturally high concentrations of fluoride (F^-) has serious health consequences in several regions across the world including South Asia, where the rural population is particularly dependent on untreated groundwater pumped from private wells. An extensive campaign to test 28,648 wells was conducted across the Punjab plains of Pakistan and India by relying primarily on field kits to document the scale of the problem and shed light on the underlying mechanisms. Groundwater samples were collected from a subset of 712 wells for laboratory analysis of F^- and other constituents. A handful of sites showing contrasting levels of F^- in groundwater were also drilled to determine if the composition of aquifer sediment differed between these sites. The laboratory data show that the field kits correctly classified 91% of the samples relative to the World Health Organization guideline for drinking water of 1.5 mg/L F^-. The kit data indicate that 9% of wells across a region extending from the Indus to the Sutlej rivers were elevated in F^- relative to this guideline. Field data indicate an association between the proportion of well-water samples with F^- > 1.5 mg/L and electric conductivity (EC) > 1.5 mS/cm across six floodplains and six intervening doabs. Low Ca²⁺ concentrations and elevated bicarbonate (HCO₃^- > 500 mg/L) and sodium (Na⁺ > 200 mg/L) in high F^- groundwater suggest regulation by fluorite. This could be through either the lack of precipitation or the dissolution of fluorite regulated by the loss of Ca²⁺ from groundwater due to precipitation of calcite and/or ion exchange with clay minerals. Widespread salinization of Punjab aquifers attributed to irrigation may have contributed to higher F^- levels in groundwater of the region. Historical conductivity data suggest salinization has yet to be reversed in spite of changes in water resources management.

A systematic review and meta-analysis of the association between fluoride exposure and neurological disorders

Different studies have suggested that fluoride is related to neurological disorders in children and adolescents, but clinical evidences of which neurological parameters associated to fluoride exposure are, in fact, still controversial. In this way, this systematic review and meta-analysis aimed to show if there is an association between fluoride exposure from different sources, doses and neurological disorders. Terms related to "Humans"; "Central nervous system"; "Fluorides"; and "Neurologic manifestations" were searched in a systematic way on PubMed, Scopus, Web of Science, Lilacs, Cochrane and Google Scholar. All studies performed on humans exposed to fluoride were included on the final assessment. A meta-analysis was then performed and the quality level of evidence was performed using the GRADE approach. Our search retrieved 4,024 studies, among which 27 fulfilled the eligibility criteria. The main source of fluoride was naturally fluoridated water. Twenty-six studies showed alterations related to Intelligence Quotient (IQ) while only one has evaluated headache, insomnia, lethargy, polydipsia and polyuria. Ten studies were included on the meta-analysis, which showed IQ impairment only for individuals under high fluoride exposure considering the World Health Organization criteria, without evidences of association between low levels and any neurological disorder. However, the high heterogeneity observed compromise the final conclusions obtained by the quantitative analyses regarding such high levels. Furthermore, this association was classified as very low-level evidence. At this time, the current evidence does not allow us to state that fluoride is associated with neurological damage, indicating the need for new epidemiological studies that could provide further evidences regarding this possible association.

Dental Fluorosis: the Risk of Misdiagnosis-a Review

Fluoride has been considered as the single factor most frequently responsible for causing enamel mottling. However, in humans, either endogenous and/or exogenous factors not related to fluoride exposure may also cause enamel mottling. In this sense, various studies in the international literature have reported severe mottling of the teeth that could not be attributed to fluoride exposure. Thus, misdiagnosis of non-fluoride-induced enamel defects may occur frequently. Reports of unexpectedly high population prevalence and individual cases of fluorosis, where such diagnoses are irreconcilable with the identified fluoride history, highlight the necessity for a more precise definition and diagnosis of dental fluorosis. Also, a more discriminating diagnostic procedure is suggested. Particularly, positive identification of environmental fluoride levels to which the communities and individuals are exposed shall be developed before the confirmation of a diagnosis of fluorosis. It is considered that a more critical methodology for the diagnosis of fluorosis will be helpful in the rational use and control of fluorides for dental health, and in the identification of factors that may induce enamel defects.

Effect of exercise on microglial activation and transcriptome of hippocampus in fluorosis mice

Fluorosis is a widespread endemic disease. Reports have shown that high fluoride causes the dysfunction of central nervous system (CNS) in animals. The neurotoxicity of fluoride may be related to the activation of microglia. Moreover, numerous studies have found that exercise facilitates the plasticity of structure and function in CNS, partly owing to the regulation of microglia activation. The present study was conducted to explore the effect of exercise on the microglial activation of hippocampus in fluorosis mice. One hundred adult female Institute of Cancer Research (ICR) mice were randomly divided into 4 groups: control group (group C, distilled water by gavage); exercise group (group E, distilled water by gavage and treadmill exercise); fluoride group [group F, 24 mg/kg sodium fluoride (NaF) by gavage]; fluoride plus exercise group (group F + E, 24 mg/kg NaF by gavage and treadmill exercise). After 8 weeks, hippocampal morphological structure, microglial activation and RNA transcriptome of mice in each group were evaluated by hematoxylin and eosin (HE) staining, Nissl staining, immunohistochemistry (IHC), quantitative real time PCR (QRT-PCR) and transcriptome sequencing. We discovered that the number of M1-type microglia in fluorosis-mice hippocampus was significantly increased when compared to group C; group F + E showed a decrease in the number of M1-type microglia with the comparison to group F. In addition, the hippocampal transcriptome analysis showed that 576 differential expression genes (DEG) were confirmed in group F, compared to group C, and 670 DEG were differently expressed in group F + E when compared to group F. Gene Ontology (GO) analysis showed that changed genes were implicated in regulation of transcription, DNA-templated, integral component of membrane and adenosine triphosphate (ATP) binding. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of 670 DEG was helpful to find neuroactive ligand-receptor interaction pathway. In conclusion, these results indicate that treadmill running inhibits the excessive activation of microglia in hippocampus of the fluoride-toxic mice, accompanied with the alteration of neuroactive ligand-receptor interaction pathway.

Refinement Impairments of Verbal-Performance Intelligent Quotient in Children Exposed to Fluoride Produced by Coal Burning

To explore the relationship between total intelligence quotient (IQ), verbal intelligence quotient (VIQ), performance intelligence quotient (PIQ), and fluoride exposure in children aged 8-12 years in coal-burning fluorosis area of Dafang County, Guizhou Province, China. The Wechsler Intelligence Scale for Children Revised in China (WISC-CR) was used to test the total IQ, VIQ, and PIQ in 99 children aged 8-12 years (55 in dental fluorosis group and 44 in control group). The differences in the intellectual levels between the two groups were compared, and the correlation between the intellectual level of children exposed to fluoride and the exposure dose of fluoride was analyzed. The VIQ, PIQ, and total IQ in the dental fluorosis group were 85.64 ± 16.53, 94.87 ± 12.73, and 88.51 ± 12.77, respectively, and these were lower than those in the control group (94.34 ± 16.04, 99.23 ± 12.44, and 96.64 ± 11.70, respectively). Significant difference was observed in VIQ and total IQ between the two groups (P = 0.002, P = 0.01), but not in the PIQ (P > 0.05). Each item of VIQ impairment (common sense, similar, arithmetic, vocabulary, and understanding) was significantly lower than those without VIQ impairment in the dental fluorosis group (P < 0.05). There was a significant difference in two items of building blocks and decoding between PIQ impairment and normal group (P < 0.05). Children with fluorosis in coal-burning areas had impaired IQ and obviously had impaired VIQ. Thus, the language learning ability should be strengthened in children exposed to fluorosis.

Fluoride exposure during pregnancy and lactation triggers oxidative stress and molecular changes in hippocampus of offspring rats

Long-term exposure to high concentrations of fluoride (F) can damage mineralized and soft tissues such as bones, liver, kidney, intestine, and nervous system of adult rats. The high permeability of the blood-brain barrier and placenta to F during pregnancy and lactation may be critical to neurological development. Therefore, this study aimed to investigate the effects of F exposure during pregnancy and lactation on molecular processes and oxidative biochemistry of offspring rats' hippocampus. Pregnant Wistar rats were randomly assigned into 3 groups in accordance with the drinking water received: G1 - deionized water (control); G2 - 10 mg/L of F and G3 - 50 mg/L of F. The exposure to fluoridated water began on the first day of pregnancy and lasted until the 21^st day of breastfeeding (when the offspring rats were weaned). Blood plasma samples of the offspring rats were collected to determine F levels. Hippocampi samples were collected for oxidative biochemistry analyses through antioxidant capacity against peroxyl (ACAP), lipid peroxidation (LPO), and nitrite (NO₂^-) levels. Also, brain-derived neurotrophic factor (BDNF) gene expression (RT-qPCR) and proteomic profile analyses were performed. The results showed that exposure to both F concentrations during pregnancy and lactation increased the F bioavailability, triggered redox imbalance featured by a decrease of ACAP, increase of LPO and NO₂^- levels, BDNF overexpression and changes in the hippocampus proteome. These findings raise novel questions regarding potential repercussions on the hippocampus structure and functioning in the different cognitive domains.

Fluoride Exposure Affects Glutamine Uptake in Müller Glia Cells

Fluoride, a pollutant present in contaminated ground water, oral care products, food, and pesticides, has deleterious effects in the structure and function of the central nervous system. Among the established neurological defects described in the exposed population, a reduced score in intelligence quotient tests in children of contaminated areas has gained attention over the past years. Maternal fluoride exposure during gestation decreases learning and memory abilities that correlate with a significant diminution of glutamate receptors expression. Since the involvement of glia cells in the maintenance and regulation of glutamatergic synapses is well-documented, in this contribution, we characterized the effect of fluoride exposure in the regulation of glia glutamine transporters. To this end, we used the Müller glia cell line, Mio-M1, and through the use of [³H]L-Glutamine uptake experiments and a Western blot approach, we demonstrate here the functional expression of system N of glutamine transporters, SNAT3 and SNAT5, in this model of human retina radial glia cells. Furthermore, these transporters interact with the glutamate transporter excitatory amino acid transporter 1, in an activity-dependent manner. Fluoride treatment reduces glutamine uptake and cell membrane [³H]glutamine surface binding, in good correlation with a decrease in SNAT3 and 5 protein levels. These results demonstrate that glia cells respond to the presence of fluoride reducing glutamine mobilization and by these means decreases glutamate turnover suggesting a disruption of glutamatergic transmission.

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.

Fluoride network and circular economy as potential model for sustainable development-A review

Fluorine is the most reactive elements among the halogen group and commonly and ubiquitously occurs as fluoride in nature. The industrial processes produce fluoride by-products causing the increase of unwanted environmental levels and consequently posing risk on human and environmental health worldwide. This review gives a fundamental understanding of fluoride networks in the industrial processes, in the geological and hydrological transport, and in the biological sphere. Numerous biological pathways of fluoride also increase the risk of exposure. Literature shows that various environmental levels of fluoride due to its chemical characteristics cause bioaccumulation resulting in health deterioration among organisms. These problems are aggravated by emitted fluoride in the air and wastewater streams. Moreover, the current waste disposal dependent on incineration and landfilling superpose to the problem. In our analysis, the fluoride material flow model still follows a linear economy and reuse economy to some extent. This flow model spoils resources with high economic potential and worsens environmental problems. Thus, we intend a shift from the conventional linear economy to a circular economy with the revival of three-dimensional objectives of sustainable development. Linkages between key dimensions of the circular economy to stimulate momentum for perpetual sustainable development are proposed to gain economic, environmental and social benefits.

The use of urinary fluoride excretion to facilitate monitoring fluoride intake: A systematic scoping review

BACKGROUND

As a recognised effective and economical agent for dental caries prevention, fluoride has been used in many different fluoridation schemes implemented across the world. Considering the narrow 'dose-gap' between the benefit of caries reduction and the risk of dental fluorosis, it is recommended that fluoride intake is monitored by measuring urinary fluoride excretion. The aim of this scoping review is to map the current literature/evidence on fluoride intake and excretion studies in relation to the study population, settings, type of study design, methodology, and analytical approach.

METHODS

Embase/Ovid, MEDLINE/Ovid, CINAHL/EBSCO, Scopus/Elsevier were searched for relevant articles until April 2018. Studies were included if they reported intake and excretion of fluoride in healthy humans of all age groups. Findings were explored using a narrative synthesis to summarise studies characteristics and outcome measures.

RESULTS

Removal of duplicates from the originally 2295 identified records yielded 1093 studies of which 206 articles were included. Only 21.6% of the studies were conducted in children (<8-year-olds). Most studies (38.8%) used drinking water concentration as a proxy for fluoride intake, whereas only 11.7% measured fluoride intake from all sources. Of the 72 studies that measured dietary fluoride intake, only 10 reported the validity of the employed dietary assessment method. Only 14 studies validated the urine sample collection methods. No information on the validity of the employed analytical method was reported by the majority (64.6%) of studies. Only a small proportion (8.7%) of the included studies investigated the association between fluoride intake and excretion.

CONCLUSION

The findings reveal much variability in terms of conducting the studies and reporting the findings, illustrating a high heterogeneity in data collection across settings and populations. Future studies should provide more detail on sampling technique, measurement protocols (including validation), and on clearly defining the relationship between intake and urinary excretion of fluoride.

Effects of Perinatal Fluoride Exposure on Short- and Long-Term Memory, Brain Antioxidant Status, and Glutamate Metabolism of Young Rat Pups

Exposure to fluoride (F) during the development affects central nervous system of the offspring rats which results in the impairment of cognitive functions. However, the exact mechanisms of F neurotoxicity are not clearly defined. To investigate the effects of perinatal F exposure on memory ability of young rat offspring, dams were exposed to 5 and 10 mg/L F during gestation and lactation. Additionally, we evaluated the possible underlying neurotoxic mechanisms implicated. The results showed that the memory ability declined in 45-day-old offspring, together with a decrease of catalase and glutamate transaminases activity in specific brain areas. The present study reveals that exposure to F in early stages of rat development leads to impairment of memory in young offspring, highlighting the alterations of oxidative stress markers as well as the activity of enzymes involved in the glutamatergic system as a possible mechanisms of neurotoxicity.

Fluoride-induced alterations of synapse-related proteins in the cerebral cortex of ICR offspring mouse brain

Fluoride (F) exposure causes cognitive dysfunction in humans and animals. However, the precise molecular mechanisms by which fluoride exerts its neurotoxic effects are poorly understood. In this study, an animal model of fluoride exposure was created by providing ICR mice were treated with vehicle F at a dose of 0 (control group), 50 (low-fluoride group) or 100 mg/L (high-fluoride group) in water for one month. After the mice mated, parents and offspring were treated and maintained under these conditions. The cognitive abilities of the mice were examined using a Morris water maze test. Results indicated that fluoride exposure significantly prolonged the escape latency period and decreased the number of crossings in a particular zone. Histopathologic analysis revealed the shrinkage and fragmentation of glial cells in the fluoride-treated groups. Pyramidal cells in the cerebral cortices of fluoride-treated groups were fewer than those of the control group. The expression of microtubule-associated protein 2 (MAP2) and synaptic proteins of the cerebral cortex in mouse offspring was assayed using RT-PCR and Western blot. Fluoride exposure possibly induced a significantly decreased expression of MAP2, synaptophysin (SYP) and developmentally regulated brain protein (Dbn) at protein and mRNA levels. Glutamate receptor (N-methyl-d-aspartate receptor, NMDAR) was also expressed, and this finding was consistent with the reduced MAP2, SYP and Dbn expression. Therefore, fluoride-mediated reduction in cognitive dysfunction is likely caused by the disruption of the expression of these synapse-associated proteins, resulting in attenuated neuronal functioning.

Dose-dependent effect of fluoride on clinical and subclinical indices of fluorosis in school going children and its mitigation by supply of safe drinking water for 5 years: an Indian study

Fluorosis is a public health problem in India; to know its prevalence and severity along with its mitigation measures is very important. The present study has been undertaken with the aim to assess the F dose-dependent clinical and subclinical symptoms of fluorosis and reversal of the disease by providing safe drinking water. For this purpose, a cross-sectional study was undertaken in 1934 schoolgoing children, Nalgonda district. Study villages were categorized into control (category I, F = 0.87 mg/L), affected (category II, F = 2.53 mg/L, and category III, F = 3.77 mg/L), and intervention categories (category IV, F = < 1.0 mg/L). School children were enrolled for dental grading by modified Dean Index criteria. Anthropometric measurements (height and weight) were used to assess nutritional status of the children. The biochemical parameters like serum T3, T4, TSH, PTH, ALP, 25-OH vitamin D, and 1,25-(OH)₂ vitamin D were analyzed. The results showed a positive correlation between the drinking water and urinary fluoride (UF) in different categories. However, there was a significant decrease in the UF levels in the intervention category IV compared to affected group (category III). Fluoride altered the clinical (dental fluorosis and stunting) and subclinical indices (urine and blood) of fluorosis in a dose-dependent manner. In conclusion, the biochemical indices were altered in a dose-dependent manner and intervention with safe drinking water for 5 years in intervention group-mitigated clinical and subclinical symptoms of fluorosis.

Association between water fluoride and the level of children's intelligence: a dose-response meta-analysis

OBJECTIVES

Higher fluoride concentrations in water have inconsistently been associated with the levels of intelligence in children. The following study summarizes the available evidence regarding the strength of association between fluoridated water and children's intelligence.

STUDY DESIGN

Meta-analysis.

METHODS

PubMed, Embase, and Cochrane Library databases were systematically analyzed from November 2016. Observational studies that have reported on intelligence levels in relation to high and low water fluoride contents, with 95% confidence intervals (CIs) were included. Further, the results were pooled using inverse variance methods. The correlation between water fluoride concentration and intelligence level was assessed by a dose-response meta-analysis.

RESULTS

Twenty-six studies reporting data on 7258 children were included. The summary results indicated that high water fluoride exposure was associated with lower intelligence levels (standardized mean difference : -0.52; 95% CI: -0.62 to -0.42; P < 0.001). The findings from subgroup analyses were consistent with those from overall analysis. The dose-response meta-analysis suggested a significant association between water fluoride dosage and intelligence (P < 0.001), while increased water fluoride exposure was associated with reduced intelligence levels.

CONCLUSIONS

Greater exposure to high levels of fluoride in water was significantly associated with reduced levels of intelligence in children. Therefore, water quality and exposure to fluoride in water should be controlled in areas with high fluoride levels in water.

Dental fluorosis, nutritional status, kidney damage, and thyroid function along with bone metabolic indicators in school-going children living in fluoride-affected hilly areas of Doda district, Jammu and Kashmir, India

A case-control study was undertaken among the school children aged 8-15 years to know the presence and severity of dental fluorosis, nutrition and kidney status, and thyroid function along with bone metabolic indicators in Doda district situated at high altitude where drinking water was contaminated and heat stress. This study included 824 participants with an age of 8-15 years. The results of the study reviled that dental fluorosis was significantly higher in affected than control area children. Urinary fluoride was significantly higher (p < 0.05) in affected children as compared to the control area school children. Nutritional status of affected children was lower than control area children. The chronic kidney damage (CKD) was higher in affected than control school children. Thyroid function was affected more in affected than control area schools. Serum creatinine, total alkaline phosphatase, parathyroid hormone, 1, 25(OH)₂ vitamin D, and osteocalcin were significantly higher in affected school children (p < 0.05) as compared to control school children, whereas there was no significant difference in triiodothyronine (T3), thyroxine (T4), and 25-OH vitamin D among the two groups. There was a significant decrease in thyroid-stimulating hormone (TSH) in the affected area school children compared to control. In conclusion, fluorotic area school children were more affected with dental fluorosis, kidney damage, along and some bone indicators as compared to control school children.

The effects of fluoride on neuronal function occurs via cytoskeleton damage and decreased signal transmission

It has been reported that fluoride exposure may cause serious public health problems, particularly neurotoxicity. However, the underlying mechanisms remain unclear. This study used Neuro-2A cells to investigate the effects of fluoride on the cytoskeleton. The Neuro-2A cells were exposed to 0, 1, 2, 4 and 6 mM sodium fluoride (NaF) for 24 h. Cell viability and lactate dehydrogenase (LDH) release were examined. It was observed that exposure to NaF reduced cell viability, disrupted cellular membrane integrity, and high levels of LDH were released. The observed changes occurred in a dose response manner. Morphologic observations showed that cell became rounded and were loosely adherent following exposure to NaF. Axon spines and normal features disappeared with high dose NaF treatment. The expression of MAP2 and synaptophysin decreased, particularly at 4 mM and 6 mM (P < 0.05) for MAP2. These results corroborate the morphologic observations. The content of glutamate and NMDAR (glutamate receptor) protein were assessed to help understand the relationship between synapses and neurotransmitter release using ELISA and Western-blot. Compared with the control, glutamate and NMDAR expression declined significantly at 4 mM and 6 mM (P < 0.05) group. Finally, the ultrastructural changes observed with increasing doses of NaF were: disappearance of synapses, mitochondrial agglutination, vacuole formation, and cellular edema. Taken together, NaF exposure disrupted cellular integrity and suppressed the release of neurotransmitters, thus effecting neuronal function. These findings provide deeper insights into roles of NaF in neuron damage, which could contribute to a better understanding of fluoride-induced neurotoxicity.

Fluoride exposure and reported learning disability diagnosis among Canadian children: Implications for community water fluoridation

OBJECTIVES

Recent studies have connected increased fluoride exposure with increased risk of neurodevelopmental-related outcomes, such as ADHD (attention deficit hyperactivity disorder) and lower IQ in children. Our primary objective was to examine the association between fluoride exposure and reported diagnosis of a learning disability among a population-based sample of Canadian children aged 3-12 years.

METHODS

We analyzed data from Cycles 2 and 3 of the Canadian Health Measures Survey. Four measures of fluoride exposure were available: 1) urinary fluoride (μmol/L), 2) creatinine-adjusted urinary fluoride (μmol/mmol), 3) specific gravity-adjusted urinary fluoride (μmol/L), and 4) fluoride concentration of tap water (mg/L) (Cycle 3 only). Diagnosis of a learning disability (yes/no) was based on parental- or self-report. Associations were examined using logistic regression (where possible), unadjusted and adjusted for covariates.

RESULTS

When Cycles 2 and 3 were examined separately, reported learning disability diagnosis was not significantly associated with any measure of fluoride exposure in unadjusted or adjusted models. When Cycles 2 and 3 were combined, a small but statistically significant effect was observed such that children with higher urinary fluoride had higher odds of having a reported learning disability in the adjusted model (p = 0.03). However, the association was not observed in models that used creatinine-adjusted urinary fluoride and specific gravity-adjusted urinary fluoride, which are believed to be more accurate measures due to their correction for urinary dilution.

CONCLUSION

Overall, there did not appear to be a robust association between fluoride exposure and parental- or self-reported diagnosis of a learning disability among Canadian children.

Evaluation of exposure to fluoride in child population of North Argentina

Fluoride is an important element for humans. It inhibits initiation and progression of dental caries and stimulates bone formation. However, excessive intake may lead to the appearance of dental and/or skeletal fluorosis and a decrease in intellectual coefficient in child populations. This study evaluates exposure to fluoride in the child population of Chaco province (Argentina) by analysis of drinking water, food and its bioaccessible fraction (quantity of fluoride solubilised by gastrointestinal digestion and available for intestinal absorption) and urine as a biomarker of internal dose. The concentration of fluoride in drinking water varied between 0.050 and 4.6 mg L^-1, and 80% of the samples exceeded the WHO drinking-water guideline value (1.5 mg L^-1). Fluoride concentrations in food ranged between 0.80 and 3.0 mg kg^-1 fresh weight (fw), being lower in bioaccessible fraction (0.43-1.9 mg kg^-1, fw). On the basis of the consumption data declared for the young child population, fluoride intake varies between 4.1 and 6.5 mg day^-1, greater than the level recommended for this age group. Moreover, in some cases, concentrations of fluoride found in urine (0.62-8.9 mg L^-1) exceeded those reported in areas with declared fluorosis. All data obtained show the worrying situation of child population in this area of Argentina.

Contributions of a Child's Built, Natural, and Social Environments to Their General Cognitive Ability: A Systematic Scoping Review

The etiology of a child's cognitive ability is complex, with research suggesting that it is not attributed to a single determinant or even a defined period of exposure. Rather, cognitive development is the product of cumulative interactions with the environment, both negative and positive, over the life course. The aim of this systematic scoping review was to collate evidence associated with children's cognitive health, including inherent factors as well as chemical and non-chemical stressors from the built, natural, and social environments. Three databases were used to identify recent epidemiological studies (2003-2013) that examined exposure factors associated with general cognitive ability in children. Over 100 factors were evaluated from 258 eligible studies. We found that recent literature mainly assessed the hypothesized negative effects of either inherent factors or chemical exposures present in the physical environment. Prenatal growth, sleep health, lead and water pollutants showed consistent negative effects. Of the few studies that examined social stressors, results consistently showed cognitive development to be influenced by both positive and negative social interactions at home, in school or the community. Among behavioral factors related to diet and lifestyle choices of the mother, breastfeeding was the most studied, showing consistent positive associations with cognitive ability. There were mostly inconsistent results for both chemical and non-chemical stressors. The majority of studies utilized traditional exposure assessments, evaluating chemical and non-chemical stressors separately. Collective evidence from a limited number of studies revealed that cumulative exposure assessment that incorporates multiple chemical and non-chemical stressors over the life course may unravel the variability in effect on cognitive development and help explain the inconsistencies across studies. Future research examining the interactions of multiple stressors within a child's total environment, depicting a more real-world exposure, will aid in understanding the cumulative effects associated with a child's ability to learn.

Effect of fluoridated water on intelligence in 10-12-year-old school children

Aim:

The aim of the present study was to evaluate the relationship of drinking water fluoride levels with children's intelligence quotient (IQ).

Materials and Methods:

Water was collected from initially identified endemic fluoride regions according to the geological research of Government of India. Fluoride concentration of the water was assessed by utilizing fluoride ion selective electrode, Orion 9609BN, and categorized on the basis of fluoride concentration into low, medium, and high-fluoride regions, i.e., Virajpet (low fluoride level < 1.2 ppm), Banavara (Medium fluoride level 1.2–2 ppm), and Mastihalli (High fluoride levels > 3 ppm). Government school from all three villages were selected randomly and IQ levels were assessed by using Raven's Standard Progressive Matrices. This test was conducted on each child in the study sample.

Results:

A significant inverse relationship was found between the fluoride concentration in drinking water and IQ (r value = −0.204; P < 0.000). It was observed that IQ level was negatively correlated with fluoride concentration in drinking water.

Conclusion:

It is concluded that IQ level was negatively correlated with fluoride level in drinking water. Factors that might affect children's IQ need to be considered, and it is necessary to devise solutions for preventing the harmful effects of excessive intake of fluoride ion to the body.

Effects of fluoride on microtubule ultrastructure and expression of Tubα1a and Tubβ2a in mouse hippocampus

Axonal and dendrictic degenerations were observed in non-skeleton fluorosis as the neurological manifestations. Microtubules, composed of the assembled tubulin dimers, are the essential cytoskeleton of axon and dendron. However, the effect of fluoride (F) on microtubules status and tubulin dimer expression in central nerves system remains largely unknown. In this study, the ultrastructure of microtubules and expression of Tubα1a and Tubβ2a were detected in hippocampus of mice orally administrated with 25, 50, or 100mgL(-1) NaF for 60d. Results showed that in F treatment groups, microtubules were broken into discrete fragments and bended, which were no longer stretched and went along the axon well. In addition, the expression of Tubα1a and Tubβ2a on both gene and protein levels were significantly reduced in high F group. The visual results of immunocytochemistry also confirmed the decreased protein expressions of Tubα1a and Tubβ2a. These findings suggested that microtubule lesions could be an important cause for neurodegeneration observed in fluorosis, and F may threaten the microtubule stability by affecting the expression of tubulin dimers.

Protective Role of tert-Butylhydroquinone Against Sodium Fluoride-Induced Oxidative Stress and Apoptosis in PC12 Cells

The neurotoxicity of fluoride is associated with oxidative stress due to imbalance between production and removal of reactive oxygen species (ROS). In contrast, induction of detoxifying and antioxidant genes through activation of NF-E2-related factor 2 (Nrf2) has been implicated in preventing oxidative stress and apoptosis in neurodegenerative diseases. The present study aimed to investigate the possible neuroprotective role of tert-butylhydroquinone (tBHQ), a general Nrf2 activator, on sodium fluoride (NaF)-induced oxidation damage and apoptosis in neuron-like rat pheochromocytoma (PC12) cells. Pretreatment with tBHQ protected PC12 cells against NaF-induced cytotoxicity as measured by MTT assay and apoptosis detection, simultaneously, inhibited NaF-induced overproduction of intracellular ROS and reduction of total glutathione content. Furthermore, NaF or tBHQ induced the stabilization of Nrf2, and enhanced expression of heme oxygenase-1 (HO-1) and γ-glutamylcysteine synthetase (γ-GCS) as a consequence of Nrf2 inducing. These findings indicated that tBHQ pretreatment conferred protective effect on PC12 cells against NaF-induced apoptotic cell death and oxidation-redox imbalance through stabilization of Nrf2 and elevation of downstream HO-1 and γ-GCS expressions.

Proteome alterations in cortex of mice exposed to fluoride and lead

Both fluoride and lead can cross the blood-brain barrier and produce toxic effects on the central neural system, resulting in low learning and memory abilities, especially in children. In order to identify the proteomic pattern in the cortex of young animals, from the beginning of fertilization to the age of postnatal day 56, pregnant female mice and pups were administrated with 150 mg sodium fluoride/L and/or 300 mg lead acetate/L in their drinking water. Two-dimensional electrophoresis (2-DE) combined with mass spectrometry (MS) was applied to identify differently expressed protein spots. Results showed that there were eight proteins in the cortex that significantly changed, whose biological functions were involved in (1) energy metabolism (Ndufs1, Atp5h, Atp6v1b2), (2) cytoskeleton (Spna2, Tuba1a, Tubb2a), (3) glycation repair (Hdhd2), and (4) cell stress response (Hspa8). Based on the previous and current studies, ATPase, Spna2, and Hspa8 were shared by fluoride and lead both as common target molecules.

Activation of the AGE/RAGE system in the brains of rats and in SH-SY5Y cells exposed to high level of fluoride might connect to oxidative stress

To explore the mechanisms by which chronic fluorosis damages the brain, we determined the levels of the advanced glycation end-products (AGEs), the receptor for AGE (RAGE), NADPH oxidase-2 (NOX2), reactive oxygen species (ROS) and malondialdehyde (MDA) in the brains of rats and/or SH-SY5Y cells exposed to different levels of sodium fluoride (5 or 50 ppm in the drinking water for 3 or 6 months and in the incubation medium for as long as 48 h, respectively). The levels of AGEs, RAGE and NOX2 protein and mRNA were measured by an Elisa assay, Western blotting and real-time PCR, respectively. The ROS content was assessed by fluorescein staining and MDA by thiobarbituric acid-reactive substance assay. In comparison to the unexposed controls, the protein and mRNA levels of AGEs, RAGE and NOX2 in the brains of rats after 6 months of exposure and in SH-SY5Y cells following high-dose exposure to fluoride were elevated. In contrast, no significant changes in these parameters were detected in the rats exposed for 3 months. In addition, the levels of ROS and MDA in the SH-SY5Y cells exposed to high-dose of fluoride were elevated in a manner that correlated positively with the levels of AGE/RAGE. In conclusion, our present results indicate that excessive fluoride can activate the AGE/RAGE pathway, which might in turn enhance oxidative stress.

Proteomic analysis of hippocampus in offspring male mice exposed to fluoride and lead

Fluoride and lead are two common pollutants in the environment. Previous investigations have found that high fluoride exposure can increase the lead burden. In this experiment, in order to study on the molecular mechanisms of central neural system injury induced by the above two elements, differently expressed protein spots in hippocampus of male mice treated with 150 mg sodium fluoride/L and/or 300 mg lead acetate/L in their drinking water were detected by two-dimensional electrophoresis (2-DE) and mass spectrometry (MS). The behavior tests showed that 56 days of fluoride and lead administration significantly reduced the vertical activity and lowered the memory ability of mice. In addition, results of 2-DE and MS revealed that nine spots demonstrated above a twofold change in the same trend in all treatment groups, which were mainly related with (1) energy metabolism, (2) cell stress response/chaperones, (3) cytoskeleton development, (4) protein metabolism, and (5) cell surface signal transduction. The findings could provide potential biomarkers for lesion in nervous system induced by fluoride and lead exposure.

Fluoride and arsenic exposure impairs learning and memory and decreases mGluR5 expression in the hippocampus and cortex in rats

Fluoride and arsenic are two common inorganic contaminants in drinking water that are associated with impairment in child development and retarded intelligence. The present study was conducted to explore the effects on spatial learning, memory, glutamate levels, and group I metabotropic glutamate receptors (mGluRs) expression in the hippocampus and cortex after subchronic exposure to fluoride, arsenic, and a fluoride and arsenic combination in rats. Weaned male Sprague-Dawley rats were assigned to four groups. The control rats drank tap water. Rats in the three exposure groups drank water with sodium fluoride (120 mg/L), sodium arsenite (70 mg/L), and a sodium fluoride (120 mg/L) and sodium arsenite (70 mg/L) combination for 3 months. Spatial learning and memory was measured in Morris water maze. mGluR1 and mGluR5 mRNA and protein expression in the hippocampus and cortex was detected using RT-PCR and Western blot, respectively. Compared with controls, learning and memory ability declined in rats that were exposed to fluoride and arsenic both alone and combined. Combined fluoride and arsenic exposure did not have a more pronounced effect on spatial learning and memory compared with arsenic and fluoride exposure alone. Compared with controls, glutamate levels decreased in the hippocampus and cortex of rats exposed to fluoride and combined fluoride and arsenic, and in cortex of arsenic-exposed rats. mGluR5 mRNA and protein expressions in the hippocampus and mGluR5 protein expression in the cortex decreased in rats exposed to arsenic alone. Interestingly, compared with fluoride and arsenic exposure alone, fluoride and arsenic combination decreased mGluR5 mRNA expression in the cortex and protein expression in the hippocampus, suggesting a synergistic effect of fluoride and arsenic. These data indicate that fluoride and arsenic, either alone or combined, can decrease learning and memory ability in rats. The mechanism may be associated with changes of glutamate level and mGluR5 expression in cortex and hippocampus.

The analog of Ginkgo biloba extract 761 is a protective factor of cognitive impairment induced by chronic fluorosis

Ginkgo biloba extract EGb761 is widely used to treat patients with learning and memory impairment in Alzheimer's disease and Parkinson's disease in China. However, it is not yet clear whether the analog of EGb761 (EGb) has a protective effect on the learning and memory damage induced by chronic fluorosis. In this study, 30 Wistar rats were randomly divided into three groups: a control group, a sodium fluoride (NaF) + EGb group, and a NaF group. The rats were administered 0.5 ml water containing NaF (100 mg/l) and EGb (120 mg/kg) per day via gavage. After 3 months, the rats' capacity for learning and memory was tested using a Y-maze. Damage to hippocampal neurons was evaluated by histological examination of the CA3 area. Superoxide dismutase (SOD) activity and the levels of glutathione peroxidase (GSH-Px) and malondialdehyde (MDA) were measured. Furthermore, the expression levels of Bcl-2 and Bax and the levels of cleaved Caspase3 in the hippocampus were evaluated by RT-PCR and Western blotting. The results showed that EGb could improve learning and memory abilities, enhance the activities of SOD and GSH-Px, attenuate the level of MDA, upregulate the ratio of Bcl-2/Bax, and downregulate the level of cleaved Caspase3.