Dr. Bill Hirzy explains how his research team quantified fluoride’s risk to the brain in a recently published study.
Fluoride & IQ: The 51 Studies
As of September 2017, a total of 58 studies have investigated the relationship between fluoride and human intelligence, and over 40 studies have investigated the relationship fluoride and learning/memory in animals. Of these investigations, 51 of the 58 human studies have found that elevated fluoride exposure is associated with reduced IQ, while 45 animal studies have found that fluoride exposure impairs the learning and/or memory capacity of animals. The human studies, which are based on IQ examinations of over 12,000 children, provide compelling evidence that fluoride exposure during the early years of life can damage a child’s developing brain.
After reviewing 27 of the human IQ studies, a team of Harvard scientists concluded that fluoride’s effect on the young brain should now be a “high research priority.” (Choi, et al 2012). Other reviewers have reached similar conclusions, including the prestigious National Research Council (NRC), and scientists in the Neurotoxicology Division of the Environmental Protection Agency (Mundy, et al). In the table below, we summarize the results from the 51 studies that have found associations between fluoride and reduced IQ and provide links to full-text copies of the studies. For a discussion of the 7 studies that did not find an association between fluoride and IQ, click here.
Quick Facts About the 50 Studies:
- Location of Studies: China (32), India (13), Iran (4), and Mexico (1).
- Sources of Fluoride Exposure: 41 of the 50 IQ studies involved communities where the predominant source of fluoride exposure was water; seven studies investigated fluoride exposure from coal burning.
- Fluoride Levels in Water: IQ reductions have been significantly associated with fluoride levels of just 0.7 to 1.2 mg/L (Sudhir 2009); 0.88 mg/L among children with iodine deficiency. (Lin 1991) Other studies have found IQ reductions at 1.4 ppm (Zhang 2015); 1.8 ppm (Xu 1994); 1.9 ppm (Xiang 2003a,b); 0.3-3.0 ppm (Ding 2011); 2.0 ppm (Yao 1996, 1997); 2.1 ppm (Das 2016); 2.1-3.2 ppm (An 1992); 2.2 ppm (Choi 2015); 2.3 ppm (Trivedi 2012); 2.38 ppm (Poureslami 2011); 2.4-3.5 ppm (Nagarajappa 2013); 2.45 ppm (Eswar 2011); 2.5 ppm (Seraj 2006); 2.5-3.5 ppm (Shivaprakash 2011); 2.85 ppm (Hong 2001); 2.97 ppm (Wang 2001, Yang 1994); 3.1 ppm (Seraj 2012); 3.15 ppm (Lu 2000); 3.94 ppm (Karimzade 2014); and 4.12 ppm (Zhao 1996).
- Fluoride Levels in Urine: About a quarter of the IQ studies have provided data on the level of fluoride in the children’s urine, with the majority of these studies reporting that the average urine fluoride level was below 3 mg/L. To put this level in perspective, a study from England found that 5.6% of the adult population in fluoridated areas have urinary fluoride levels exceeding 3 mg/L, and 1.1% have levels exceeding 4 mg/L. (Mansfield 1999) Although there is an appalling absence of urinary fluoride data among children in the United States, the excess ingestion of fluoride toothpaste among some young children is almost certain to produce urinary fluoride levels that exceed 2 ppm in a portion of the child population.
Methodological Limitations
As both the NRC and Harvard reviews have correctly pointed out, many of the fluoride/IQ studies have used relatively simple designs and have failed to adequately control for all of the factors that can impact a child’s intelligence (e.g., parental education, socioeconomic status, lead and arsenic exposure). For several reasons, however, it is unlikely that these limitations can explain the association between fluoride and IQ.First, some of the fluoride/IQ studies have controlled for the key relevant factors, and significant associations between fluoride and reduced IQ were still observed. This fact was confirmed in the Harvard review, which reported that the association between fluoride and IQ remains significant when considering only those studies that controlled for certain key factors (e.g., arsenic, iodine, etc). Indeed, the two studies that controlled for the largest number of factors (Rocha Amador 2007; Xiang 2003a,b) reported some of the largest associations between fluoride and IQ to date.
Second, the association between fluoride and reduced IQ in children is predicted by, and entirely consistent with, a large body of other evidence. Other human studies, for example, have found associations between fluoride, cognition, and neurobehavior in ways consistent with fluoride being a neurotoxin. In addition, animal studies have repeatedly found that fluoride impairs the learning and memory capacity of rats under carefully controlled laboratory conditions. An even larger body of animal research has found that fluoride can directly damage the brain, a finding that has been confirmed in studies of aborted human fetuses from high-fluoride areas.
Finally, it is worth considering that before any of the studies finding reduced IQ in humans were known in the western world, a team of U.S. scientists at a Harvard-affiliated research center predicted (based on behavioral effects they observed in fluoride-treated animals) that fluoride might be capable of reducing IQ in humans. (Mullenix 1995)
Summary
When considering their consistency with numerous animal studies, it is very unlikely that the 50 human studies finding associations between fluoride and reduced IQ can all be a random fluke. The question today, therefore, is less whether fluoride reduces IQ, but at what dose, at what time, and how this dose and time varies based on an individual’s nutritional status, health status, and exposure to other contaminants (e.g., aluminum, arsenic, lead, etc). Of particular concern is fluoride’s effect on children born to women with suboptimal iodine intake during the time of pregnancy, and/or fluoride’s effects on infants and toddlers with suboptimal iodine intake themselves. According to the U.S. Centers for Disease Control, approximately 12% of the U.S. population has deficient exposure to iodine.
Studies Finding Association Between Fluoride & Reduced IQ:
| Citation: | Bashash M, Thomas D, Hu H, Angeles Martinez-Mier E, et al. (2017). Prenatal Fluoride Exposure and Cognitive Outcomes in Children at 4 and 6–12 Years of Age in Mexico. Environmental Health Perspectives, Sep 19;125(9):097017. |
| Location of Study: | Participants from the Early Life Exposures in Mexico to Environmental Toxicants (ELEMENT) project. |
| Size of Study: | 299 mother–child pairs, of whom 287 and 211 had data for the General Cognitive Index and IQ analyses, respectively. |
| Age of Subjects: | Tests of cognitive function in the offspring at age 4 and 6–12 years. |
| Source of Fluoride: | Fluoridated salt (at 250?ppm) and to varying degrees of naturally occurring fluoride in drinking water. |
| Water Fluoride Level: | Natural water fluoride levels in Mexico City may range from 0.15 to 1.38 mg/L |
| Type of IQ Test: | “At age 4 y, neurocognitive outcomes were measured using a standardized version of McCarthy Scales of Children’s Abilities. For children 6–12 y old a Spanish-version of the Wechsler Abbreviated Scale of Intelligence.” |
| Results: | “In multivariate models we found that an increase in maternal urine fluoride of 0.5mg/L (approximately the IQR) predicted 3.15 (95% CI: ?5.42, ?0.87) and 2.50 (95% CI ?4.12, ?0.59) lower offspring GCI and IQ scores, respectively.” |
| Conclusions: | “In this study, higher prenatal fluoride exposure, in the general range of exposures reported for other general population samples of pregnant women and nonpregnant adults, was associated with lower scores on tests of cognitive function in the offspring at age 4 and 6–12 y.” |
| IQ Study #50: (Das 2016) | |
| Citation: | Das K, Mondal NK. (2016). Dental fluorosis and urinary fluoride concentration as a reflection of fluoride exposure and its impact on IQ level and BMI of children of Laxmisagar, Simlapal Block of Bankura District, W.B., India. Environmental Monitoring & Assessment 188(4):218. |
| Location of Study: | West Bengal, India |
| Size of Study: | 149 schoolchildren |
| Age of Subjects: | 6 to 18 |
| Source of Fluoride: | Water |
| Water Fluoride Level: | Average = 2.1 mg/L (S.D. = 1.64 mg/L) |
| Type of IQ Test: | Combined Raven’s Test for RuralChina (CRT-RC) |
| Results: | “IQ has anegative significant correlation with dental fluorosis (r=0.253,P<0 .01="" a="" acts="" an="" as="" consequence="" considered="" correlation="" decreasing="" dental="" dose="" exposure="" fluoride="" fluorosis="" has="" indicator="" input="" iq.="" iq="" is="" level="" nbsp="" negative="" of="" p="" r="0.343, P<0.01)" significant="" so="" source.="" was="" which="" with=""> “IQ values were plotted against the urinary fluoride concentration and it was found that they have a significant negative correlation (r=0.751, P<0 .01="" p=""> |
| Conclusion | “[C]hildren residing in areas with higher than normal water fluoride level demonstrated more impaired development of intelligence and moderate [dental fluorosis]. Millions of children including adults around the world are affected by higher level of fluoride concentration through their drinking water and are therefore potentially at risk. It is concluded that for the benefit of the future generation, urgent attention should be paid on this substantial public health problem.” |
| IQ Study #49: Mondal (2016) | |
| Citation: | Mondal D, et al. (2016). Inferring the fluoride hydrogeochemistry and effect of consuming fluoride-contaminated drinking water on human health in some endemic areas of Birbhum district, West Bengal. Environmental Geochemistry & Health 38(2):557-76. |
| Location of Study: | Birbhum district, India |
| Size of Study: | 40 children (20 from endemic fluorosis area; 20 from control area) |
| Age of Subjects: | 10 to 14 years old |
| Source of Fluoride: | Water |
| Water Fluoride Levels: | “Mean F concentration in the study area varies from 0.32 to 13.29 mg/L.” |
| Type of IQ Test: | Raven Standard Theoretical Intelligence Test |
| Results: | “This study indicates that students exposed to high F (children of Junidpur and Nowapara) show an average IQ of 21.17 ± 6.77 in comparison with low-F exposed students (children of Bilaspur, Mohula, Bhalian) having an average IQ of 26.41 ± 10.46. . . . Statistical analysis (Z test) demonstrates that there is a significant (Z = 2.59) difference in IQ among the high- and low-F area student.” |
| Conclusion | “[S]tudents of the study area have less IQ than students of
non-contaminated area, demonstrating that consumption of F also has a
major role with the intellectual development of children.” |
| IQ Study #48: Khan (2015) | |
| Citation: | Khan SA, et al. (2015). Relationship between dental fluorosis and intelligence quotient of school going children in and around Lucknow district: a cross-sectional study. Journal of Clinical & Diagnostic Research 9(11):ZC10-15. |
| Location of Study: | Lucknow district, India. |
| Size of Study: | 429 schoolchildren |
| Age of Subjects: | 6-12 years old |
| Source of Fluoride: | Water |
| Results: | “In this study, on comparison of children at two locations according to IQ grades [Table/Fig-4], majority of the children (74.8%) living in low fluoride area had an IQ grade 2 (definitely above the average in intellectual capacity). None of the children from the low fluoride area had an IQ grade 4 and 5 (definitely below average and intellectually impaired). On the other hand, majority of children (58.1%) from high fluoride area fall under IQ grade 3 (intellectually average). None of the children from high fluoride area had an IQ grade 1 (intellectually superior). This difference in IQ grades of children amongst the two areas was found to be statistically significant (p<0 .001="" a="" and="" between="" capacity="" clearly="" correlation="" decrease="" evident="" fluorosis="" grade="" in="" increase="" indicating="" intellectual="" iq="" is="" observed="" of="" p="0.766).”</td" pearman="" s="" strong="" t="" that="" the="" trend="" was="" with=""> |
| Conclusion: | “The data from this research may support the hypothesis that excess fluoride in drinking water has toxic effects on the nervous system.” |
| IQ Study #47: Sebastian (2015) | |
| Citation: | Sebastian ST, Sunitha S. 2015. A cross-sectional study to assess the intelligence quotient (IQ) of school going children aged 10-12 years in villages of Mysore district, India with different fluoride levels. Journal of the Indian Society of Pedodontics and Preventive Dentistry 33(4):307-11. |
| Location of Study: | Mysore district, India |
| Size of Study: | 405 schoolchildren (135 children from high fluoride area; 135 children from “normal” fluoride area; 135 chidren from “low” fluoride area) |
| Age of Subjects: | 10-12 years old |
| Source of Fluoride: | Water |
| Water Fluoride Levels: | High-fluoride: 2.2 mg/L; “Normal” Fluoride: 1.2 mg/L; “Low” Fluoride: 0.4 mg/L |
| Type of IQ Test: | Raven’s colored Progressive Matrices Test |
| Results: | “In bivariate analysis, significant relationships were found between water fluoride levels and Intelligence Quotient of school children (P < 0.05). In the high fluoride village, the proportion of children with IQ below 90, i.e. below average IQ was larger compared to normal and low fluoride village. Age, gender, parent education level and family income had no significant association with IQ.” |
| Conclusion: | “School children residing in area with higher than normal water fluoride level demonstrated more impaired development of intelligence when compared to school children residing in areas with normal and low water fluoride levels.” |
| IQ Study #46: Kundu (2015) | |
| Citation: | Kundu H, et al. (2015). Effect of fluoride in drinking water on children’s intelligence in high and low fluoride areas of Delhi. Journal of the Indian Association of Public Health Dentistry 13(2):116-121. April-June. |
| Location of Study: | Delhi, India. |
| Size of Study: |
200 school children: 100 from low F area and 100 from high F area.
|
| Age of Subjects: | 8-12 years of age.
Equal numbers of male and female children were included in the study.
|
| Source of Fluoride: | Water |
| Type of Cognitive Tests: |
Ravens Standardized Progressive Matrices Test
|
| Results: | “Comparison of mean IQ of children in both high (76.20 ± 19.10) and low F (85.80 ± 18.85) areas showed a significant difference (P = 0.013). Multiple regression analysis between child IQ and all other independent variables revealed that mother’s diet during pregnancy (P = 0.001) along with F in drinking water (P = 0.017) were the independent variables with the greatest explanatory power for child IQ variance (r2 = 0.417) without interaction with other variables.” |
| Conclusion: | “Fluoride in the drinking water was significantly related with the IQ of children. Along with fluoride, mother’s diet during pregnancy was also found to be significantly related with IQ of children.” |
| IQ Study #45: Choi (2015) | |
| Citation: | Choi A, et al. (2015). Association of lifetime exposure to fluoride and cognitive functions in Chinese children: A pilot study. Neurotoxicology & Teratology 47:96-101. |
| Location of Study: | Southern Sichuan Province, China. |
| Size of Study: | 51 children from elevated fluoride area |
| Age of Subjects: | Avg = 7.1 years old |
| Source of Fluoride: | Water |
| Urine Fluoride Levels: | Mean = 1.64 mg/L; Range = 0.22 to 5.84 mg/L |
| Water Fluoride Levels: | Mean = 2.2 mg/L; Range = 1.0 to 4.07 mg/L |
| Confounding Factors: |
“In this rural community, social differences are limited. The parents
or guardians completed a questionnaire on demographic and personal
characteristics including the child’s sex, age at testing, parity,
illnesses before age 3, past medical history of the child and
caretakers, parental or guardian age, education and occupational
histories, and residential history, and household income. It is known
that iron deficiency can impair motor and mental developments in
children, iron concentration was therefore considered as a covariate.
These potential confounders were used for adjustment in the statistical
analysis.” “Among possible confounders, both arsenic and lead are known to be low in drinking water in the area.” |
| Type of Cognitive Tests: | WRAML, WISC-R, WRAVMA |
| Results: | “Results of our pilot study showed that moderate and severe dental fluorosis was significantly associated with deficits in WISC-R digit span. Children with moderate or severe dental fluorosis scored significantly lower in total and backward digit span tests than thosewith normal or questionable fluorosis. These results suggest a deficit in working memory. Scores on other tests did not show significant relationships with indices of fluoride exposure.” |
| Conclusion: | “Results of our field study raise a concern about the safety of elevated systemic exposure to fluoride from high concentrations in the drinking water.While topical fluoride treatment confers benefits of reducing caries incidence, the systemic exposure should not be so high as to impair children’s neurodevelopment especially during the highly vulnerable windows of brain development in utero and during infancy and childhood and may result in permanent brain injury. We are planning a larger scale study to better understand the dose–effect relationships for fluoride’s developmental neurotoxicity in order to characterize the appropriate means of avoiding neurotoxic risks while securing oral health benefits.” |
| IQ Study #44: Zhang (2015) | |
| Citation: | Zhang S, et al. (2015). Modifying Effect of COMT Gene Polymorphism and a Predictive Role for Proteomics Analysis in Children’s Intelligence in Endemic Fluorosis Area in Tianjin, China. Toxicological Sciences 144(2):238-45. April. |
| Location of Study: | Tianjin City, China |
| Size of Study: | 180 children (96 from control area; 84 from “high fluoride” area) |
| Age of Subjects: | Avg = 11 years old |
| Source of Fluoride: | Water |
| Water Fluoride Levels: | High = 1.4 mg/L Control = 0.63 mg/L |
| Urine Fluoride Levels: | High = 2.4 + 1.01 mg/L Control = 1.10 + 0.67 mg/L |
| Serum Fluoride Levels: | High = 0.18 + 0.11 mg/L Control = 0.06 + 0.03 mg/L |
| Type of IQ Test: | Combined Raven’s Test for Rural China (CRT-RC) |
| Confounding Factors: | “Covariates included the indicator variables for age, gender, educational levels of parents (primary and below, junior high school, senior high school, and above), and continuous variables for drinking water fluoride (mg/l) and levels of thyroid hormones (T3, T4, and TSH).” |
| Results: | “[T]he present work demonstrated that the IQ scores of children exposed to high fluoride drinking water were significantly lower than those who lived in control area . . . . [O]ur findings further showed that, across the full range of serum and urinary fluoride, children’s IQ decreased gradually with the increase of fluoride contents in serum and urine, in a dose-dependent manner.” |
| Conclusion: | “In summary, our data suggest that the intelligence of children is affected by the COMT gene polymorphism and, in particular, this SNP plays a role in modifying the effect of fluoride exposure on cognition. Children with COMT reference allele had a higher risk for cognitive impairments after fluoride exposure. Additionally, proteomics analysis represents early specific markers of developmental fluoride neurotoxicity. Hence, our findings provide certain basis for clarifying the mechanisms and identifying molecular targets of pharmacological interventions for potential delayed therapy.” |
| IQ Study #43: Bai (2014) | |
| Citation: | Bai Z, et al. (2014) Investigation and analysis of the development of intelligence levels and growth of children in areas suffering fluorine and arsenic toxicity from pollution from burning coal. Chinese Journal of Endemiology 33(2):160-163. |
| Location of Study: | Shaanxi Province, China. |
| Size of Study: | 303 children (120 children from high-fluoride area; 95 from mid-fluoride area, 98 from low-fluoride area) |
| Age of Subjects: | 8 to 12 years old |
| Source of Fluoride | Coal burning |
| Urine Fluoride Levels: | “The median urinary fluoride levels for children 8–12 years old in the areas of significant, minor and no morbidity were, respectively, 1.96, 0.81 and 0.54 mg/L.” |
| Results: | “The children’s urinary fluoride and urinary arsenic levels versus intelligence [quotients] were both negatively correlated (r=-0.560, -0.353, all P<0 .05="" td=""> |
| Conclusion | “Exposures to fluorine and arsenic are deleterious to the development of intelligence and the development of growth in children” |
| IQ Study #42: Wei (2014) | |
| Citation: | Wei N, et al. (2014). The effects of comprehensive control measures on intelligence of school-age children in coal-burning-borne endemic fluorosis areas. Chinese Journal of Endemiology 33(3):320-22. |
| Location of Study: | Bijie City, Guizhou Provinc, China. |
| Size of Study: | 741 children (104 children from low-fluoride area; 298 children from an endemic fluorosis area with long-term defluoridation measures; 339 children from endemic fluorosis area with short-term defluoridation measures). |
| Age of Subjects: | 8-12 years old |
| Source of Fluoride: | Coal |
| Urinary Fluoride Levels: | Control: 1.34 ± 0.64 mg/L; Long-term defluoridation: 2.33 ± 0.18 mg/L; Short-term defluoridation: 3.03 ± 0.16) mgL. |
| Results: | “Above average IQ of children in the control group was 97.1% (101/104),which was significantly higher than that of long and short treatment groups; after a lengthy treatment, mental retardation detection rate was significantly lower in the low-age group,8-10 year-old children(x2 =7.542,P < 0.01). Urinary fluoride content was negatively correlated with the level of IQ (r =-0.553,P < 0.01).“ |
| Conclusion: | “The intelligence development of children in coal-burning-borne endemic fluorosis area is significantly delayed. After a certain period of comprehensive treatment,the decreased level of cognition is inhibited and the mental retardation in the low-age group is improved.” |
| IQ Study #41: Nagarajappa (2013) | |
| Citation: | Nagarajappa R, et al. (2013). Comparative assessment of intelligence quotient among children living in high and low fluoride areas of Kutch, India: a pilot study. Iranian Journal of Public Health 2(8): 813–818. |
| Location of Study: | Kutch District, Gujarat, India |
| Size of Study: | 100 children (50 children from high-fluoride area; 50 children from control area) |
| Age of Subjects: | 8-10 years old |
| Source of Fluoride: | Water |
| Water Fluoride Levels: | High Fluoride: 2.4 to 3.5 mg/L; Control: 0.5mg/L. |
| Type of IQ Test: | Seguin Form Board Test |
| Results: | “Mean scores for average, shortest and total timing category were found to be significantly higher (P<0 .05="" 21.78="" 7.24="" 7.28="" 95="" among="" and="" at="" be="" bhuj="" children="" confidence="" differences="" for="" found="" in="" interval="" living="" mean="" mundra="" respectively.="" td="" than="" these="" those="" timings="" to="" were=""> |
| Conclusion: | “Chronic exposure to high levels of fluoride in water was observed to be associated with lower intelligence quotient.” |
| IQ Study #40: Singh (2013) | |
| Citation: | Singh VP, et al. (2014). A correlation between serum vitamin, acetylcholinesterase activity and IQ in children with excessive endemic fluoride exposure in Rajasthan, India. European Academic Journal 2(4):5857-5869. |
| Location of Study: | Jaipur, Rajasthan (India) |
| Size of Study: | 42 children (70 from high-fluoride area; 72 from control area) |
| Age of Subjects: | 9 to 14 year olds |
| Source of Fluoride: | Water |
| Levels of Fluoride in Water: | High Fluoride = 6.8 mg/L Control area = <1 .03="" mg="" td=""> |
| Confounding Factors: | “The subjects were similar in living conditions, parental literacy, socioeconomic status, and health history. Moreover, age and sex matched controls were selected from the [low-fluoride area].” |
| Type of IQ Test: | Raven’s Test |
| Conclusion: | “We observed reduced AChE activity in [the high fluoride area] which may be directly correlate[d] with the reduced intelligence score of the subjects.” |
| IQ Study #39: Karimzade (2014) | |
| Citation: | Karimzade S, et al. (2014). Investigation of intelligence quotient in 9-12-year-old children exposed to high- and low-drinking water fluoride in West Azerbaijan province, Iran. Fluoride 47(1):9-14. |
| Location of Study: | Poldashi and Piranshahr, West Azerbaijan province, Iran. |
| Size of Study: | 39 male children (19 from high-fluoride area; 20 from control area) |
| Age of Subjects: | 9 to 12 year olds |
| Source of Fluoride: | Water |
| Water Fluoride Levels: | High Fluoride = 3.94 mg/L Control = 0.25 mg/L |
| Confounding Factors: | No significant differences were found in the potential confounding factors of educational, economic, social, cultural, and general demographic characteristics between the high- and low-F regions. |
| Type of IQ Test: | Iranian version of the Raymond B Cattell test |
| Results: | “The IQ of the 19 children in the high-F region was lower (mean±SD: 81.21±16.17), than that of the 20 children in the low-F region (mean±SD: 104.25±20.73, p=0.0004). In the high-F region, 57.8% had scores indicating mental retardation (IQ <70 10="" 70="" borderline="" figure="" in="" intelligence="" low="" only="" or="" region.="" td="" the="" this="" was="" while=""> |
| Conclusions: | “The study found that children residing in a region with a high drinking water F level had lower IQs compared to children living in a low drinking water F region (p<0 .001="" and="" attributed="" be="" confounding="" could="" cultural="" demographic="" differences="" economic="" educational="" factors.="" general="" not="" social="" td="" the="" to=""> |
| IQ Study #38: Trivedi (2012) | |
| Citation: | Trivedi MH, et al. (2012). Assessment of groundwater quality with special reference to fluoride and its impact on IQ of schoolchildren in six villages of the Mundra Region, Kachchh, Gujurat, India. Fluoride 45(4):377-83. |
| Location of Study: | Gujurat, India |
| Size of Study: | 84 children (34 from high-fluoride villages, 50 children from control village) |
| Age of Subjects: | 6th and 7th grade students |
| Source of Fluoride: | Water |
| Water Fluoride Levels: | High Fluoride = 2.3 + 0.87 mg/L Control = 0.83 + 0.38 mg/L |
| Urine Fluoride Levels: | High Fluoride = 2.69 + 0.92 mg/L Control = 0.42 + 0.23 |
| Confounding Factors: | Same socioeconomic status (E on an A-E scale); same attendance status at school (regular students attending more than 80% of classes) |
| Type of IQ Test: | Questionnaire prepared by Prof. JH Shah; standardized on the Gujarati population with 97% reliability rate in relation to the Stanford-Binet Intelligence Scale |
| Results: | “The average IQ score of the 34 students drinking the high F water was significantly lower (p?0.05) than among the 50 students drinking the low F water.” |
| Conclusions: | “the present investigation concludes that the three villages of Chhasara, Gundala, and Mundra, are F-contaminated villages. Because of high F concentrations in the [groundwater], children in these villages have greater exposure to F that may lead in to low IQ as compared to the nearby villages of Baroi, Zarpara, and Pragpar, which have low F in their [groundwater].” |
| IQ Study #37: Seraj (2012) | |
| Citation: | Seraj B, et al. (2012). Effect of high water fluoride concentration on the intellectual development of children in Makoo/Iran. Journal of Dentistry, Tehran University of Medical Sciences 9(3): 221-29. |
| Location of Study: | Makoo, Iran. |
| Size of Study: | 293 children (91 children in control village; 106 children in medium F village; 96 children in high F village) |
| Age of Subjects: | 6 to 11 years old |
| Source of Fluoride Exposure: | Water |
| Water Fluoride Levels: | Control = 0.8+0.3 ppm Medium fluoride = 3.1+0.9 ppm High fluoride = 5.2+1.1 ppm |
| Confounding Factors: | Age, gender, child’s educational level, mother’s educational level, father’s educational level, fluorosis intensity, iodine level in water, lead level in water. |
| IQ Test: | Raven’s Color Progressive Matrices (RCPM) |
| Results: | “The mean IQ scores decreased from 97.77+18.91 for the normal fluoride group to 89.03+12.99 for the medium fluoride group and to 88.58+16.01 for the high fluoride group (P=0.001).” |
| Conclusion: | “Since all potentially confounding factors were adjusted, the difference in IQ scores may reveal the potential effect of high fluoride exposure on the intellectual development of children.” |
| IQ Study #36: Saxena (2012) | |
| Citation: | Saxena S, et al. (2012). Effect of fluoride exposure on the intelligence of school children in Madhya Pradesh, India. Journal of Neurosciences in Rural Practice 3(2):144-49. |
| Location of Study: | Madhya Pradesh, India. |
| Size of Study: | 173 children (120 children in three high-F areas and 53 children from a control group) |
| Age of Subjects: | School children in the 5th & 6th grades |
| Source of Fluoride Exposure: | Water |
| Water Fluoride Levels: | Group 1 = >4.5 ppm Group 2 = 3.1-4.5 ppm Group 3 = 1.5-3.0 ppm Control = <1 .5="" ppm="" td=""> |
| Urine Fluoride Levels: | Group 1 = 7.01+1.02 Group 2 = 4.85+0.50 Group 3 = 3.28+0.48 Control = 2.25+0.28 |
| Confounding Factors: | (1) No significant differences in urinary lead, arsenic, or iodine levels between the four groups. (2) No significant differences in gender ratio, socio-economic status, SES, parental education, height/age ratio, and weight/height ratio. (3) Children were excluded if they were not lifelong resident of area, if they had changed their water source since birth, or if they had history of congenital or acquired neurological disease and/or head injury. |
| IQ Test: | Raven’s Standard Progressive Matrices |
| Results: | “Reduction in intelligence was observed with an increased water fluoride level (P 0.000). The urinary fluoride level was a significant predictor for intelligence (P 0.000).” |
| Conclusion: | “This study indicates that exposure to fluoride is associated with reduced intelligence in children. We have found a significant inverse relationship between intelligence and the water fluoride level, and intelligence and the urinary fluoride level. After adjusting for confounders, urinary fluoride was the significant predictor for intelligence.” |
| IQ Study #35: Ding (2011) | |
| Citation: | Ding Y, et al. (2011). The relationships between low levels of urine fluoride on children’s intelligence, dental fluorosis in endemic fluorosis areas in Hulunbuir, Inner Mongolia, China. Journal of Hazardous Materials 186(2-3):1942-46. |
| Location of study: | Hulunbuir, Inner Mongolia, China |
| Size of study: | 331 children from four sites |
| Age of Subjects: | 7-14 years old |
| Source of Fluoride: | Water |
| Water Fluoride Levels: | Mianduhe town=0.28+0.03 mg/L Nan district=0.79+0.33 mg/L Donghu district=1.78+0.60 mg/L Zhalainuoer county=1.82+1.00 mg/ |
| Urine Fluoride Levels: | No dental fluorosis = 0.80+0.55 mg/L Questionable fluorosis = 1.13+0.73 mg/L Very mild fluorosis = 1.11+0.74 mg/L Mild fluorosis = 1.31+0.78 mg/L Moderate fluorosis =1.46+0.79 mg/L. |
| Confounding Factors: | (1) Sites selected to match social and natural factors like economic situation, educational standard, and geological environments. (2) Schools had similar teaching quality. (3) Sites are not exposed to known neurotoxins (e.g. arsenic) in drinking water, nor are they endemic areas for iodine deficiency disorders. (4) Five children who had not lived in these areas at least 1 year were excluded. |
| IQ Test: | CRT-RC3 (Combined Raven’s Test for Rural China) |
| Results: | Children’s IQ was inversely related to urinary fluoride content, (p<0 .0001="" 0.59="" 1="" associated="" decrease="" each="" f="" in="" increase="" iq="" mg="" of="" p="0.0226).</td" point="" urine="" was="" with=""> |
| Conclusion: | “In conclusion, our study suggested that low levels of fluoride exposure in drinking water had negative effects on children’s intelligence and dental health and confirmed the dose-response relationships between urine fluoride and IQ scores as well as dental fluorosis.” |
| IQ Study #34: Poureslami (2011) | |
| Citation: | Poureslami HR, et al. (2011). Intelligence quotient of 7 to 9 year-old children from an area with high fluoride in drinking water. Journal of Dentistry and Oral Hygiene 3(4):61-64. |
| Location of study: | Kerman Province, Iran: Koohbanan (high-F) and Baft (low-F) |
| Size of study: | 120 children: 60 children per city |
| Age of Subjects: | 7-9 years old |
| Source of Fluoride: | Water |
| Water Fluoride levels: | High-F = 2.38 mg/L Low-F = 0.41 mg/L |
| Confounding Factors: | (1) Exclusion criteria: genetic, congenital, or acquired diseases related to the nervous system, past or present. (2) Inclusion criteria (high-F village): signs of grade III TSIDF (total surface index of Dental Fluorosis) or more. (3) Inclusion criteria (low-F village): similar physical and mental health criteria adopted, but children lacked any sign of Dental Fluorosis. (4) Both towns at high altitude. |
| Type of IQ Test | Raven’s Progressive Matrices Intelligence Test (Persian version) |
| Results: | Average IQ of High F group (91.37+16.63) is significantly lower than average IQ of Low-F group (97.80+15.95), p < 0.05. |
| Conclusion: | “Based on the findings, chronic exposure to high levels of fluoride can be one of the factors that influence intellectual development.” |
| IQ Study #33: Eswar (2011) | |
| Citation: | Eswar P, et al. (2011). Intelligent quotients of 12-14 year old school children in a high and low fluoride village in India. Fluoride 44:168-72. |
| Location of study: | Ajjihalli (low F) and Holesirigere (high F) villages, Davangere district, Karnataka, India. |
| Size of study: | 133 children total (low F village=65; high F village=68) |
| Age of Subjects: | 12-14 years old |
| Source of Fluoride: | Water |
| Water Fluoride levels: | High F village=2.45 mg/L Low F village =0.29 mg/L |
| Confounding Factors: | (1) Children included were continuous residents of study villages since birth; drinking water from same public water supply (1 per village); (2) attended same high school (1 per village). (3) Children with history of trauma or injury to head; affected by congenital or acquired neurological disorders, psychological disorders were excluded. |
| Type of IQ Test | Raven’s Standard Progressive Matrices Test |
| Results: | 63.2% of children in high F area had IQ less than 90, versus 47.7% of children in low F village. (p=0.06). |
| Conclusion: | “Though there was a trend in our study towards lower IQ in a greater number of children from high F village than in the low F village, probably the small sample size of the present study failed to establish a statistically significant difference.” |
| IQ Study #32: Shivaprakash (2011) | |
| Citation: | Shivaprakash PK, et al. (2011). Relation between dental fluorosis and intelligence quotient in school children of Bagalkot district. J Indian Soc Pedod Prev Dent. 29(2):117-20. |
| Location of study: | Bagalkot district, Karnataka state, India |
| Size of study: | 160 children |
| Age of Subjects: | 7-11 years old |
| Source of Fluoride: | Water |
| Water Fluoride Levels: | high F village = 2.5-3.5 mg/L low F village = < 0.5 mg/L |
| Confounding Factors: | (1) Children included in study had normal birth history, were permanent residents in the region of study, had no history of trauma to the head, no history of chronic illness, not on medication. (2) Villages have similar culture, standard of living, and lifestyle habits. |
| Type of IQ Test | Raven’s Colored Progressive Matrices Test |
| Results: | (A) Children with dental fluorosis had lower IQ (66.63+18.09) than those without dental fluorosis (76.36+20.84), p < 0.05. (B) Children with mild dental fluorosis had lower IQ (66.73) than those without dental fluorosis (75.89), p < 0.05. |
| Conclusion: | “Previous studies had indicated toward decreased Intelligence in children exposed to high levels of fluoride and our study also confirmed such an effect.” |
| IQ Study #31: Sudhir (2009) | |
| Citation: | Sudhir KM, et al. (2009). Effect of fluoride exposure on
intelligence quotient (IQ) among 13-15 year old school children of known
endemic area of fluorosis, Nalgonda District, Andhra Pradesh. Journal of the Indian Association of Public Health Dentistry 13:88-94. |
| Location of Study: | Nalgonda District, Andhra Pradesh, India |
| Size of Study: | 1000 children |
| Age of Subjects: | 13-15 years old |
| Source of Fluoride: | Water |
| Water Fluoride Levels: | Four areas were studied: <0 .7="" 0.7-1.2="" 1.2-4.0="" mg="">4 mg/L |
| Type of IQ Test: | Raven’s standard progressive matrices |
| Results: | “Number of intellectually impaired children were gradually increased with the increase in fluoride concentration in the drinking water.” |
| Conclusion: | “Findings of this study suggest that overall IQ levels in children’s exposed to high fluoride level were significantly lower than the low fluoride areas.” |
| IQ Study #30: Li (2009) | |
| Citation: | Li F, et al. (2009). The impact of endemic fluorosis caused by the burning of coal on the development of intelligence in children. Journal of Environmental Health 26(4):838-40. |
| Location of study: | Xinhua County, Hunan Province, China |
| Size of study: | 80 children total: 20 children from “mild” fluorosis area, 20 from “medium” fluorosis area, 20 from “severe” fluorosis area, and 20 from non-fluorosis area. |
| Age of Subjects: | 8-12 years old |
| Source of Fluoride: | Coal burning |
| Fluoride exposure levels: |
Urine F (by region): severe = 2.34+1.13 mg/L medium = 1.67+0.66 mg/L mild = 1.24+0.43 mg/L control = 0.96+0.52 mg/L Urine F (by dental fluorosis type): severe = 2.66+1.09 mg/L medium = 2.01+0.80 mg/L mild = 1.64+0.68 mg/L very mild = 1.17+0.48 mg/L suspected = 1.09+0.36 mg/L no fluorosis = 0.87+0.23 mg/L. |
| Confounding Factors: | (1) All children were born and raised in the respective areas. (2) Children were excluded if they had been diagnosed with physical deformation, developmental disorders, delayed mental development, emotional/behavioral obstacles or challenges, or other forms of mental disorders. |
| Type of IQ Test | CRT-RC (Combined Raven’s Test for Rural China) |
| Results: | – IQ decreased with increasing F level in urine (p < 0.01) – IQ was significantly reduced among children with severe fluorosis as compared to children without fluorosis (p < 0.05) – A trend (albeit not statistically significant) for IQ to decrease with increasing severity of dental fluorosis (NS) and with increasing severity of the region’s fluoride poisoning |
| Conclusion: | “High exposure to fluoride most definitely has an adverse effect on the development of intelligence in children, in particular on the capability of abstract inference.” |
| IQ Study #29: Rocha-Amador (2007) | |
| Citation: | Rocha-Amador D, et al. (2007). Decreased intelligence in children and exposure to fluoride and arsenic in drinking water. Cadernos de Saude Publica 23(Suppl 4):S579-87. |
| Location of study: | Durango State, Mexico & San Luis Potosi State, Mexico |
| Size of study: | 132 children |
| Age of Subjects: | 6 to 10 years old |
| Source of Fluoride Exposure: | Water |
| Water Fluoride Levels | Lowest F village: 0.8+1.4 mg/L Middle F village: 5.2+0.9 mg/L Highest F village: 9.4+0.9 mg/L |
| Urine Fluoride Levels | Lowest F village: 1.8+1.5 mg/L Middle F village: 6.0+1.6 mg/L Highest F village: 5.5+3.3 mg/L |
| Confounding Factors: | (1) A multiple regression analysis was used that controlled for blood lead levels, socioeconomic status, mother’s education, height-for-age (an index of malnutrition), and transferrin saturation. (2) Each child’s water fluoride level, and urine fluoride level, levels were individually determined. (3) The test examiner was blinded as to the children’s fluoride exposure. |
| IQ Test: | Wechsler Intelligence Scale for Children–Revised Mexican Version (WISC-RM) |
| Results: | (1) Both fluoride in urine, and fluoride in water, were significantly correlated with IQ, and this correlation remained significant after controlling for lead exposure, socioeconomic status, mother’s education, malnutrition, and transferrin. (2) Fluoride’s effect on IQ was larger than the effect from arsenic. |
| Conclusion: | “We found that exposure to F in urine was associated with reduced Performance, Verbal and Full IQ scores before and after adjusting for confounders. The same pattern was observed for models with F in water as the exposure variable. . . . The individual effect of F in urine indicated that for each mg increase of F in urine a decrease of 1.7 points in Full IQ might be expected.” |
| IQ Study #28: Wang (2007) | |
| Citation: | Wang SX, et al. (2007). Arsenic and fluoride exposure in drinking water: children’s IQ and growth in Shanyin county, Shanxi province, China. Environmental Health Perspectives 115(4):643-7. |
| Location of study: | Shanyin County, Shanxi Province, China |
| Size of study: | 720 children: 21-196 per village (3 villages for each of the arsenic groups) |
| Age of Subjects: | 8-12 years old |
| Source of Fluoride: | Water |
| Water Fluoride Levels: | High-Arsenic group = 0.9+0.5 mg/L Medium-Arsenic group = 1.7+1.1 mg/L High-Fluoride group = 8.3+1.9 mg/L Control group = 0.5+0.2 mg/L |
| Urine Fluoride levels: | High-Arsenic group = 1.0+1.7 mg/L Medium-Arsenic group = 2.8+1.9 mg/L High-Fluoride group = 5.1+2.0 mg/L Control group = 1.5+1.6 mg/L |
| Confounding Factors: | (1) Arsenic used as variable. Similar manganese levels in water for all groups. (2) All groups lived in rural areas with similar geographic and cultural conditions and a comparable level of socioeconomic development (years of parental education, average income, years of exposure). (3) All children currently attending school. |
| Type of IQ Test | CRT-RC (Combined Raven’s Test for Rural China) |
| Results: | – Average IQ in high-arsenic area (95.1+16.6) is significantly lower than IQ in control area (104.8+14.7). p < 0.05 – The average IQ in high-fluoride area (100.5+15.8) is also significantly lower than average IQ in control area (104.8+14.7). p < 0.05 – Significantly more children with IQ lower than 70 (mental retardation) in high-F area (4%), medium-arsenic area (3.3%), and high-arsenic area (8.3%) as compared to control (0%). |
| Conclusion: | “This study indicates that exposure to fluoride in drinking water is associated with neurotoxic effects in children.” |
| IQ Study #27: Trivedi (2007) | |
| Citation: | Trivedi MH, et al. (2007). Effect of high fluoride water on intelligence of school children in India. Fluoride 40(3):178-183. |
| Location of study: | – High F area: Sachana, Sanand district, Gujarat, India – Medium F area: Chandlodia, Ahmedabad, India |
| Size of study: | 190 children (89 in high F area; 101 in medium F area) |
| Age of Subjects: | 12-13 years old |
| Source of Fluoride: | Water |
| Water Fluoride Levels: | High F area=5.55+0.41 mg/L Medium F area=2.01+0.009 mg/L |
| Urine Fluoride Levels: | High F area = 6.13+0.67 mg/L Medium F area = 2.30+0.28 mg/L |
| Confounding Factors: | (1) The study included only those children who were life-long residents of the areas. respective location. (2) The areas have similar nutritional status and both have middle class socioeconomic status (although Sachana is slightly poorer). (3) Iodized salt is used in both areas. |
| Type of IQ Test | Questionnaire prepared by Prof. JH Shah; standardized on the Gujarati population with 97% reliability rate in relation to the Stanford-Binet Intelligence Scale |
| Results: | (A) Average IQ is lower in High-F area (91.72+1.13) than in Low-F area (104.44+1.23), p<0 .001.="" 28.09="" area="" below="" children="" f="" found="" has="" igh="" in="" iq="" lower="" nbsp="" normal="" of="" over="" percentage="" td="" the="" twice="" with=""> |
| Conclusion: | “In agreement with other studies elsewhere, these findings indicate that children drinking high F water are at risk for impaired development of intelligence.” |
| IQ Study #26: Fan (2007) | |
| Citation: | Fan Z, et al. (2007). The effect of high fluoride exposure on the level of intelligence in children. Journal of Environmental Health 24(10):802-03. |
| Location of study: | Pucheng County, Shaanxi Province, China. |
| Size of study: | 79 children (42 children in High F area; 37 children in low F area) |
| Age of Subjects: | 7-14 years old |
| Source of Fluoride: | Water |
| Water Fluoride Levels: | – High F area=3.15 mg/L – Low F area=1.03 mg/L (water-improvement schemes implemented 14-18 years before study) |
| Urine Fluoride Levels: | – High F area group=2.89+1.97 mg/L (range: 1.14-6.09 mg/L); – Low F area group=1.78+0.46 mg/L (range: 1.33-2.35 mg/L) (non-significant difference, likely because F is consumed from various sources other than water) |
| Confounding Factors: | (1) The two areas have common habits and lifestyles in terms of cuisine, economy, culture, education, agricultural goods, etc.. (2) No chemical factories in area. (3) The area does not have an iodine deficiency problem. |
| Type of IQ Test | CRT-C2 intelligence module |
| Results: | (A) Average IQ in High-F area (96.11 + 12.00) is lower than Low-F area (98.41 + 14.75), although difference is not statistically significant. (B) No child in High-F area has outstanding or excellent intelligence. The respective rates in the Low-F area are 2.7% and 5.4%, respectively. |
| Conclusion: | “Exposure to high levels of fluoride is likely to cause a certain level of harm to a child’s level of intelligence.” |
| IQ Study #25: Seraj (2006) | |
| Citation: | Seraj B, et al. (2006). [Effect of high fluoride concentration in drinking water on children’s intelligence]. [Study in Persian] Journal of Dental Medicine 19(2):80-86. |
| Location of study: | Iran |
| Size of study: | 126 children (85 children from low-F village, 41 children from high-F village) |
| Age of Subjects: | Not provided in English abstract (full study is in Persian) |
| Source of Fluoride: | Water |
| Water Fluoride Levels: | High F village = 2.5 mg/L Low F village = 0.4 mg/L |
| Confounding Factors: | The history of illnesses affecting the nervous system, head trauma, birth weight (>2.5kg or < 2.5kg), residental history, age and sex of children were investigated by questionnaires completed by the children’s parents. |
| Type of IQ Test | Raven’s |
| Results: | “In the high fluoride area the mean IQ of children (87.9±11) was significantly lower than in the low fluoride area (98.9±12.9) (P=0.025).” |
| Statistical significance | ““Based on the findings of this study, exposure of children to high levels of fluoride may carry the risk of impaired development of intelligence.” |
| IQ Study #24: Wang (2005) | |
| Citation: | Wang S, et al. (2005). The effects of endemic fluoride poisoning caused by coal burning on the physical development and intelligence of children. Journal of Applied Clinical Pediatrics 20(9):897-898 (republished in Fluoride 2008; 41:344-348). |
| Location of study: | Zhijin County, Ghizhou Province, China |
| Size of study: | 226 children (176 children in High F area, including 119 children with skeletal fluorosis and 57 children with only dental fluorosis; 50 children in low-F area without skeletal or dental fluorosis) |
| Age of Subjects: | 7-12 years old |
| Type of Exposure: | Coal burning |
| Urine Fluoride Levels: | High F group=1.352+0.457 mg/L (n=144) Lower F group=1.611+0.467 mg/L (n=35) |
| Confounding Factors: | (1) Both areas are free from iodine deficiency. (2) Both areas have similar standard of living, sanitation, culture, and availability of medical treatment. |
| Type of IQ Test | Raven’s Standard Theoretical Intelligence Test, Chinese version |
| Results: | Children from high F (endemic) areas had lower IQ than those from lower F (control) area (p<0 .01="" and="" between="" correlation="" f="" iq="" negative="" p="" td="" urine=""> |
| Conclusion: | “High fluoride burden has a definite effect on the intellectual and physical development of children.” |
| IQ Study #23: Xiang (2003a), Xiang, (2003b) | |
| Citation: | – Xiang Q, et al. (2003a). Effect of fluoride in drinking water on children’s intelligence. Fluoride 36: 84-94. – Xiang Q, et al. (2003b). Blood lead of children in Wamiao-Xinhuai intelligence study. Fluoride 36: 198-199. |
| Location of study: | Sihong County, Jiangsu Province, China |
| Size of study: | 512 children (222 children in high-F village, 290 children in low-F village) |
| Age of Subjects: | 8-13 years old |
| Type of Exposure: | Water |
| Water Fluoride Levels: | High F village=2.47+0.79 mg/L (range=0.57-4.50 mg/L) Low F village=0.36+0.15 mg/L (range=0.18-0.76 mg/L)In the high-F village, children were subdivided into the following five fluoride water levels:Group A<1 .0="" br="" mg=""> Group B=1.0-1.9 mg/L; Group C=2.0-2.9 mg/L; Group D=3.0-3.9 mg/L; Group E>3.9 mg/L. |
| Urine Fluoride Levels: | High F village=3.47+1.95 mg/L Low F village=1.11+0.39 mg/L |
| Confounding Factors: | (1) The two villages have similar urine iodine levels (p>0.3), and blood lead levels (p>0.48). (2) Neither village has fluoride pollution from burning coal or other industrial sources. (3) None of the residents reported drinking brick tea. (4) Children who had been absent from either village for 2 years or longer, or who had a history of brain disease or head injury were excluded from study. |
| Type of IQ Test | CRT-RC (Combined Raven’s Test for Rural China) |
| Results: | (A) Mean IQ of high F village (92.02+13.00) is lower than low F village (100.41+13.21), p<0 .01.="" and="" are="" associated="" borderline="" children="" drinking="" education="" f="" family="" higher="" income="" intelligence="" iodine="" iqs="" is="" level.="" mental="" not="" of="" or="" p="" parent="" rates="" related="" retardation="" s="" significantly="" td="" to="" urinary="" water="" with=""> |
| Conclusion: | “In endemic fluorosis areas, drinking water fluoride levels greater than 1.0 mg/L may adversely affect the development of children’s intelligence.” |
| IQ Study #22: Li (2003) | |
| Citation: | Li Y, et al. (2003). Effects of endemic fluoride poisoning on the intellectual development of children in Baotou. Chinese Journal of Public Health Management 19(4):337-338 (republished in Fluoride 2008; 41:161-64). |
| Location of study: | Baotou, Inner Mongolia, China |
| Size of study: | 936 children (720 children from high-F endemic area; 236 children from low-F control area) |
| Age of Subjects: | 6-13 years old |
| Source of F exposure: | Water |
| Fluoride exposure levels: | “The region classified as endemic was designated using the 1981 standards for designation of endemic regions laid out in 1981’s Standards for Endemic Fluorosis Prevention and Treatment Work” |
| Type of IQ Test | Illustrated version of the Chinese Standardized Raven Test for children in rural areas |
| Results: | (A) Average IQ of children in endemic area (92.07) somewhat lower than that of control area (93.78), NS. (B) Rate of children with low IQ (<69 area="" but="" control="" endemic="" given="" greater="" high="" in="" no="" p="" significance="" statistical="" td="" than="" value=""> |
| Conclusion: | “In our study, we found that the average IQ of children in a fluoride endemic area was somewhat lower than the control, but the result was not statistically significant (p > 0.05). The percentage of children with fluorosis, however, was higher as compared to the control, and this was very significant statistically.” |
| IQ Study #21: Shao (2003) | |
| Citation: | Shao Q, et al. (2003). Study of cognitive function impairment caused by chronic fluorosis. Chinese Journal of Endemiology 22(4):336-38. |
| Location of study: | Bijie City (high F area) and Tongren area (control area), Guizhou Province, China |
| Size of study: | 88 adults (49 adults in High-F area; 39 adults in Low-F area) |
| Age of Subjects: | Aged 30-50 (High-F area = 42+6 years; Low-F area = 43+6 years) |
| Source of Fluoride Exposure: | Water |
| Fluoride exposure levels: | Adults in high-F area diagnosed as suffering from fluoride poisoning (as evident by dental and skeletal changes). Water F levels not provided. |
| Confounding Factors: | Non-iodine deficient areas. Exclusions of mental disorders caused by mental retardation, brain organic and somatic diseases. All farmers. Similar distribution of age, sex, education level. |
| Type of IQ Test | Wechsler Adult Intelligence Scale test for Rural China (WATS-RC); Associated learning (AL) test; Digit Span (DS) test; Similarity test; Speech fluency test (SFT); Comprehension test. |
| Results: | (A) Significantly lower operation score on IQ test in high F area (48-54) versus low F area (52-59), p < 0.01. (B) Lower total IQ score in high F area (78-100, average) than in low F area (109-118, average-high), although not statistically significant (C) High F subjects have significantly lower scores on several of the performance tests (speech fluency, recognition, similarity, p < 0.01, and digit span, p < 0.05), and this correlates with elevated levels of oxidative stress. |
| Conclusion: | “The results suggest that some cognitive function limitations exist in those suffering from chronic fluoride poisoning, and its biologic basis may be related to the levels of SOD and NO [indices of oxidative stress].” |
| IQ Study #20: Wang (2001) | |
| Citation: | Wang X, et al. (2001). Effects of high iodine and high fluorine on children’s intelligence and thyroid function. Chinese Journal of Endemiology 20(4):288-90. |
| Location of study: | Binzhou and Dezhou, Qingyun County, Shandong Province, China |
| Size of study: | 513 children (322 children from school in high iodine/high fluoride area; 193 children from school in lower iodine/lower fluoride area). |
| Age of Subjects: | 8-12 years old |
| Source of Fluoride Exposure: | Water |
| Water Fluoride Levels: | – High iodine/high fluoride area=2.97 mg/L – Lower iodine/lower fluoride area=0.5 mg/L |
| Urine Fluoride Levels: | – High iodine/high fluoride = 3.08+1.03 mg/L – Low iodine/low fluoride = 0.82+0.56 mg/L |
| Type of IQ Test | CRT-RC (Combined Raven’s Test for Rural China) |
| Results: | (A) Average IQ is lower in High-F area than in Low-F area (76.67+7.75 vs. 81.67+11.97), although the difference does not reach statistical significance. (B) The rate of extremely low and borderline IQ is higher in the High F areas than in the Low F areas (16.67% vs. 10% and 36.67% vs. 16.67, respectively), although these differencese do not reach statistical significance. |
| Conclusion: | “High iodine and high fluorine have certain influence on children’s intelligence and thyroid function.” |
| IQ Study #19: Hong (2001) | |
| Citation: | Hong F, et al. (2001). Research on the effects of fluoride on child intellectual development under different environmental conditions. Chinese Primary Health Care 15(3):56-57 (republished in Fluoride 2008; 41(2):156–60). |
| Location of study: | Wukang, Boxing, and Zouping counties, Shangdong Province, China |
| Size of study: | 205 children (32 controls; 85 High F; 32 High-F/High Iodine; 28 High F/Low Iodine; 28 Low F/Low Iodine) |
| Age of Subjects: | 8-14 years old |
| Source of Fluoride Exposure: | Water |
| Water Fluoride Levels: | – Control area = 0.75 mg/L – High F only = 2.90 mg/L – High F/High I = 2.85 mg/L – High F/Low I = 2.94 mg/L – Low F/Low I = 0.48 mg/L |
| Confounding Factors: | – Areas have same geographical features and standard of living. |
| Type of IQ Test | Chinese Standardized Raven’s Test for Rural areas (CRT-R) |
| Results: | (A) Average IQ of High F/Low I group (68.38+19.12) and Low F/Low I group (75.53+6.92) is lower than control group (82.79+8.98), p<0 .01.="" and="" between="" compared="" control="" deficits="" exists="" f="" fluoride="" group="" groups="" high="" i="" interaction="" iodine="" iq="" is="" low="" lower="" of="" ow="" p="" ranking="" show="" significant="" td="" than="" to=""> |
| Conclusion: | “The IQ results of this study show no significant difference between the average IQs of those children from the high fluoride only areas and the high fluoride/high iodine areas, however the result from the high fluoride/low iodine group show statistically significant differences as compared to that of the low fluoride/low iodine group. In short, it appears that the presence or lack of iodine is a more significant factor in both the prevalence of goiter and average IQ.” |
| IQ Study #18: Lu (2000) | |
| Citation: | Lu Y, et al (2000). Effect of high-fluoride water on intelligence of children. Fluoride 33:74-78. |
| Location of study: | Tianjin Xiqing District, China |
| Size of study: | 118 children (60 children in High-F village; 58 children in Low-F village) |
| Age of Subjects: | 10-12 years old |
| Source of Fluoride Exposure: | Water |
| Water Fluoride Levels: | – High F village = 3.15+0.61 mg/L – Low F village = 0.37+0.04 mg/L |
| Urine Fluoride Levels: | – High F village = 4.99+2.57 mg/L – Low F village = 1.43+0.64 mg/L |
| Confounding Factors: | (1) Children included in the study are lifelong residents of study area. (2) Villages have similar population size, social, economic and educational backgrounds. (3) Children with congenital or acquired neurological disorders were excluded. |
| Type of IQ Test | Chinese Combined Raven’s Test, Copyright 2 (CRT-C2) |
| Results: | (A) Average IQ of children from High F village (92.27+20.45) is lower than children from Low F village (103.05+13.86), p<0 .005.="" and="" between="" borderline="" children="" exists="" f="" group="" high="" in="" intelligence="" inverse="" iq.="" low="" more="" p="" relationship="" retarded="" significant="" td="" than="" urinary=""> |
| Conclusion: | “The findings of this study thus replicate those of earlier studies and suggest that a real relationship exists between fluoride exposure and intelligence.” |
| IQ Study #17: Zhang (1998) | |
| Citation: | Zhang J, et al. (1998). The effect of high levels of arsenic and fluoride on the development of children’s intelligence. Chinese Journal of Public Health 17(2):119. |
| Location of Study: | Kuitun region, Urumqi, China |
| Size of Study: | 164 children |
| Age of Subjects: | 4-10 years old |
| Source of Fluoride Exposure: | Water |
| Water Fluoride Levels: | For the 4 to 8 year olds, the fluoride level their entire life (including during fetal development) was between 0.49 and 0.81 ppm. The 9 year olds were exposed to high fluoride (level not provided) during fetal development. The 10 year olds were exposed to high fluoride during fetal development and their first year of life. |
| Type of IQ Test: | 50-point evaluation tests created by Japanese researcher, Shigeo Kobayashi |
| Results: | No difference in IQ among the 4 to 8 year olds, a slight (non-significant) reduction in IQ among the 9 year olds (who were exposed to fluoride during fetal development), and a significant reduction among the 10 year olds (who were exposed during fetal development and their first year of life). |
| Conclusion: | “Even though there were differences in the results from the 10 year-old subjects from the normal comparative group, in contrast to subjects from the high fluoride high arsenic group and the high fluoride group, these results might not be overtly representative as less number of subjects from the high fluoride group has been tested.” |
| IQ Study #16: Yao (1997) | |
| Citation: | Yao Y, et al. (1997). Comparative assessment of the physical and mental development of children in endemic fluorosis area with water improvement and without water improvement. Literature and Information on Preventive Medicine 3(1):42-43. |
| Location of study: | Chaoyang City, Liaoning Province, China |
| Size of study: | 823 children (326 children from fluorosis area with water improvement; 183 children from fluorosis area without water improvement; 314 children from non-fluorosis area) |
| Age of Subjects: | 7-14 years old |
| Source of Fluoride Exposure: | Water |
| Water Fluoride Levels: | – Fluorosis area without water improvements = 2.0 mg/L- Fluorosis with water improvements = 0.33 mg/L (prior to improvement 8 years before study, the F level was 2.0 mg/L)- Non-fluorosis area = 0.4 mg/L |
| Confounding Factors: |
– All children born locally. – Areas in study have adequate iodine exposure and similar levels of economic development, living conditions, school size, and number of teachers. |
| Type of IQ Test | CRT-RC (Combined Raven’s Test for Rural China) |
| Results: | (A) Children in fluorosis area (without water improvement) have lower average IQ than children in fluorosis area (with water improvement) for all age groups, p<0 .01.="" after="" age="" all="" and="" area.="" area="" average="" between="" born="" children="" difference="" exists="" fluorosis="" for="" groups="" have="" improvement="" in="" intelligence="" iq="" lower="" no="" non-fluorosis="" p="" prior="" program="" significant="" td="" than="" to="" water="" with="" without=""> |
| Conclusion: | “These results show that water improvement and defluoridation can improve the mental and physical development of children in a fluorosis area.“ |
| IQ Study #15: Yao (1996) | |
| Citation: | Yao Y, et al. (1996). Analysis on TSH and intelligence level of children with dental Fluorosis in a high fluoride area. Literature and Information on Preventive Medicine 2(1):26-27. |
| Location of study: | Chaoyang City, Liaoning Province, China |
| Size of study: | 536 children (78 children from high-fluorosis area; 188 children from light-fluorosis area; 270 children from non-fluorosis area) |
| Age of Subjects: | 8-12 years old |
| Source of Fluoride Exposure: | Water |
| Water Fluoride Levels: | High-F area: <11 mg/L Low-F area: 2.0 mg/L Control area: 1.0 mg/L |
| Confounding Factors: | (1) Children in each of the three areas have adequate iodine exposure as determined through urine analysis. (2) The three areas have similar economic development, schools, and teachers. |
| Type of IQ Test | Raven test—Associative Atlas (Version of Chinese village) |
| Results: | (A) Average IQ of children with dental fluorosis in high-fluorosis area and light-fluorosis areas is lower than children in non-fluorosis area, p<0 .01.="" area="" average="" children="" dental="" fluorosis="" from="" high-fluorosis="" high="" iq="" is="" light-fluorosis="" lower="" of="" p="" rate="" than="" those="" with="">120) is lower in high-fluorosis area (3.85%) and light-fluorosis area group (6.91%) than non-fluorosis area (10.74%) (no p value given). |
| Conclusion: | “The results of the intelligence tests show that a high level of fluoride influences children’s IQ, which is consistent with some previous data. It is worth mentioning that the higher the degree of dental fluorosis, the more negative the impact on the children’s intelligence level. This is an issue which merits utmost attention.” |
| IQ Study #14: Zhao (1996) | |
| Citation: | Zhao LB, et al. (1996). Effect of high-fluoride water supply on children’s intelligence. Fluoride 29: 190-192. |
| Location of study: | Shanxi Province, China |
| Size of study: | 320 children (160 children from high-F village; 160 children from lower-F village) |
| Age of Subjects: | 7-14 years old |
| Source of Fluoride Exposure: | Water |
| Water Fluoride Levels: | High-F village = 4.12 mg/L Lower-F village = 0.91 mg/L |
| Confounding Factors: | (1) Similar occupations, living standards, and social customs in the two villages. (2) Only children whose mothers lived in the village during pregnancy were included in study. (3) Parents’ educational level was determined (and found to have a significant influence on IQ, p < 0.01). |
| Type of IQ Test | “Official intelligence quotient (IQ) tests lasting 40 minutes” |
| Results: | Children in High-F village have significantly lower average IQ (97.69+13.00) than children in lower-F village (105.21+14.99), p<0 .01.="" td=""> |
| Conclusion: | “The results of this study indicate that intake of high-fluoride drinking water from before birth has a significant deleterious influence on children’s IQ in one of two similar villages.” |
| IQ Study #13: Wang (1996) | |
| Citation: | Wang G, et al. (1996). A study of the IQ levels of four- to seven-year-old children in high fluoride areas. Endemic Diseases Bulletin 11(1):60-6 (republished in Fluoride 2008; 41:340–43). |
| Location of study: | Shehezi, Xinjiang Province, China |
| Size of study: | 230 children (147 children from High-F village; 83 children from Low-F village) |
| Age of Subjects: | 4-7 years old |
| Source of Fluoride Exposure: | Water & Coal-Burning |
| Water Fluoride Levels: | – All wells = 0.58-8.60 mg/L – High F area = > 1.0 mg/L – Low F area = < 1.0 mg/L |
| Confounding Factors: | (1) Children were excluded from study if they had a low intellectual ability due to genetic inheritance, past illness, malnutrition, uses of medication, or other reasons. (2) “Significantly greater” percentage of children with below average head circumference in High F area (18.37%) than in Control area (9.64%) (no p value given). |
| Type of IQ Test | Wechler Preschool and Primary Scale of Intelligence (WPPSI) |
| Results: | (A) Average Total IQ in High F group (95.64+14.34) is lower than in control group (101.23+15.84), p<0 .05.="" average="" f="" group="" high="" in="" iq="" performance="" span="" style="text-decoration: underline;">+ |
Fluoride is a poison. Fluoride was poison yesterday. Fluoride is poison today. Fluoride will be poison tomorrow. Think of the millions of dollars we are spending to "school" our children. Does it not make sense to give our children the best environment in which to grow? Ask your dental hygienist if she has read the literature on how fluoride is lowering the IQ of our children. When in doubt get it out.
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