Fluoride Action Network

Fluoride & Intelligence: The 37 Studies

brain_scan02
Fluoride Action Network | By Michael Connett & Tara Blank, PhD | UPDATED Feb. 19, 2014
  • A A A
  • As of May 2013, a total of 43 studies have investigated the relationship between fluoride and human intelligence, and a total of 31 studies have investigated the relationship fluoride and learning/memory in animals. Of these investigations, 37 of the 43 human studies have found that elevated fluoride exposure is associated with reduced IQ, while 29 of the 31 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 11,000 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 37 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 6 studies that did not find an association between fluoride and IQ, click here.

    Quick Facts About the 37 Studies:

    • Location of Studies: China (28), India (5), Iran (3), and Mexico (1).
    • Sources of Fluoride Exposure: 31 of the 37 IQ studies involved communities where the predominant source of fluoride exposure was water; six studies investigated fluoride exposure from coal burning.
    • Fluoride Levels in Water: IQ reductions have been significantly associated with fluoride levels of just 0.88 mg/L among children with iodine deficiency. (Lin 1991) Other studies have found IQ reductions at 1.4 ppm (Zhang 2012); 1.8 ppm (Xu 1994); 1.9 ppm (Xiang 2003a,b); 0.3-3.0 ppm (Ding 2011); 2.0 ppm (Yao 1996, 1997); 2.1-3.2 ppm (An 1992); 2.3 ppm (Trivedi 2012); 2.38 ppm (Poureslami 2011); 2.45 ppm (Eswar 2011); 2.5 ppm (Seraj 2006); 2.85 ppm (Hong 2001); 2.97 ppm (Wang 2001, Yang 1994); 3.1 ppm (Seraj 2012); 3.15 ppm (Lu 2000); and 4.12 ppm (Zhao 1996).
    • Fluoride Levels in Urine: 13 of the 37 IQ studies have provided data on the level of fluoride in the children’s urine. 8 of these 12 studies reported that the average urine fluoride level was below 4 mg/l, and 6 reported average fluoride levels below 3 mg/L. To put these levels 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 extremely 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 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 37 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:

    IQ Study #37: 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
    Controls for 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 #36: Zhang (2012)
    Citation Zhang X. (2012). Studies of relationships between the polymorphism of COMT gene and plasma proteomic profiling and children’s intelligence in high fluoride areas. Master’s Dissertation, Huazhong University of Science & Technology, May 2012.
    Location of Study: Tianjin, China
    Age of Subjects: 5th grade students (avg age = 11 yrs)
    Source of Fluoride: Water
    Water Fluoride Levels: High-Fluoride: 1.40 + 1.3 mg/L
    Low-Fluoride: 0.63 + 0.07 mg/L
    Urine Fluoride Levels High-Fluoride: 2.19 + 0.93 mg/L
    Low-Fluoride: 0.80 + 0.29 mg/L
    Blood Fluoride Levels High-Fluoride: 0.20 + 0.09 mg/L
    Low-Fluoride: 0.04 + 0.04 mg/L
    Type of IQ Test: Chinese Combined Raven’s Test Picture Book
    Controls for Confounding Factors: “Controlling for societal, economic, educational, geographical, and environmental factors, we randomly selected 68 Grade 5 students from areas in Tianjin with drinking water fluoride concentrations lower than 1.0 mg/L as our control group, and 55 Grade 5 students from areas with fluoride concentrations higher than 1.0 mg/L as our high fluoride group, for a total of 123 subjects.”
    Results: (1) “A Spearman rank correlation analysis reveals a positive correlation between drinking water, urine, and blood serum fluoride concentrations (r=0.372, P<0.05; r=0.2378, P<0.05). There is a clear negative correlation between IQ score and urine and blood serum fluoride concentrations (r =-0.155, P<0.05; r=-0.154, P<0.05).”(2) “The difference in blood serum TSH between the high-fluoride (2.67 + 0.67 mg/L) and control groups (3.7 + 2.12 mg/L) is statistically significant, but the differences in blood serum T3 (2.22 + 0.37 mg/L vs. 2.15 + 0.43 mg/L) and T4 (85.7 + 17.11 vs. 90.8 + 11.92) between the two groups is not statistically significant.”
    Conclusion: “In summary, we found that negative correlations exist between child IQ and both blood serum and urine fluoride concentrations in areas with fluoride poisoning.”
    IQ Study #35: 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
    Controls for 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 #34: 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
    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
    Controls for 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 #33: 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.
    Controls for 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). Each increase in 1 mg/L of urine F was associated with 0.59 point decrease in IQ (p=0.0226).
    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 #32: 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
    Controls for 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 #31: 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
    Controls for 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 #30: 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
    Controls for 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 #29: 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/LUrine 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.
    Controls for 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 #28: 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
    Controls for 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 #27: 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
    Controls for 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 #26: 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
    Controls for 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. (B) High F area has 28.09% of children with IQ below normal (over twice the percentage found in lower F area).
    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 #25: 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)
    Controls for 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 #24: 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
    Controls for 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 #23: 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)
    Controls for 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). Negative correlation between urine F and IQ (p<0.01).
    Conclusion:  “High fluoride burden has a definite effect on the intellectual and physical development of children.”
    IQ Study #22: 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 mg/L;
    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
    Controls for 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. (B) Higher drinking water F is significantly associated with higher rates of mental retardation (IQ<70) and borderline intelligence (IQ=70-79), p<0.05. (C) Children’s IQs are not related to urinary iodine, family income, or parent’s education level.
    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 #21: 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”
    Controls for Confounding Factors: None given.
    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) greater in endemic area (10.38%) than in control area (4.24%) (“high statistical significance”, but no p value given).
    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 #20: 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.
    Controls for 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 #19: 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
    Controls for Confounding Factors: Iodine exposure.
    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 #18: Hong (2001)
    Citation: Hong F, et al. (2001). Research on the effects of fluoride on child intellectual development under different environments. 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
    Controls for Confounding Factors: - Iodine exposure. – 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. (B) IQ of High F/Low I group is lower than Low F/Low I group, p<0.01. (C) Significant interaction exists between High Fluoride and Low Iodine, p<0.01. (D) IQ ranking of high F groups show significant deficits compared to control, p<0.01.
    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 #17: 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
    Controls for 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. (B) More “retarded” (IQ=<70) and “borderline” intelligence (IQ=70-79) children in high F group (21.6%) than in low F group (3.4%), p<0.005. (C) Significant inverse relationship exists between urinary F and IQ.
    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 #16: 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.
    Controls for Confounding Factors:  Arsenic level in water.
    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 #15: 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
    Controls for 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. (B) Children in fluorosis area without water improvement have lower average IQ than children in non-fluorosis area for all age groups, p<0.01. (C) Children born prior to water improvement program in fluorosis area with water improvement have lower average IQ than children in non-fluorosis area, p<0.05. (D) No significant difference in intelligence exists between children born after water improvement and children in non-fluorosis area.
    Conclusion: “These results show that water improvement and defluoridation can improve the mental and physical development of children in a fluorosis area.“
    IQ Study #14: 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
    Controls for 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. (B) Average IQ of children with dental fluorosis from high-fluorosis area is lower than those from light-fluorosis area, p<0.05. (C) Rate of high IQ (>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 #13: 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
    Controls for 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.
    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 #12: 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
    Controls for 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. (B) Average Performance IQ in High F group (94.33+14.76) is lower than in Control group (101.77+18.12), p<0.01. (C) Average Verbal IQ is not significantly different. (D) In High F area, children with below-normal head circumference have lower average IQ (89.07+15.69) than those with normal head circumference (97.13+8.06), p<0.01.
    Conclusion “The results show that a high fluoride intake has a clear influence on the IQ of preschool children, manifesting itself primarily as damage to performance intelligence.”
    IQ Study #11: Li (1995)
    Citation: Li XS, et al. (1995). Effect of fluoride exposure on intelligence in children. Fluoride 28:189-192.
    Location of study: Anshu and Zhijin counties, Guizhou Province, China
    Size of study: 907 children (230 children from severe fluorosis area; 224 children from medium fluorosis area; 227 children from slight fluorosis area; 226 children from non-fluorosis area)
    Age of Subjects: 8-13 years old
    Source of Fluoride Exposure: Coal burning
    Urine Fluoride Levels - Severe dental fluorosis = 2.69 mg/L – Medium dental fluorosis = 2.01 mg/L – Slight dental fluorosis = 1.81 mg/L – No dental fluorosis = 1.02 mg/L
    Controls for Confounding Factors: (1) All children of Han nationality.(2) Children were excluded from study if they had  congenital or acquired diseases “not related to fluoride.” (3) Groups separated by intervals of 6 months in age.
    Type of IQ Test China Rui Wen’s Scaler for Rural Areas
    Results: Average IQ of children in severe (80.3+12.9) and medium (79.7+12.7) fluorosis areas is lower than the slight (89.7+12.7) and non-fluorosis (89.9+10.4) areas, p<0.01.
    Conclusion: “A high fluoride intake was associated with a lower intelligence.”
     IQ Study #10: Xu (1994)
    Citation: Xu Y, et al. (1994). The effect of fluorine on the level of intelligence in children. Endemic Diseases Bulletin 9(2):83-84.
    Location of study: Shandong Province, China
    Size of study: 330 children (8 groups of 21-97 children categorized based on fluoride and iodine content of water)
    Age of Subjects: 8-14 years old
    Source of Fluoride Exposure: Water
    Water Fluoride Levels: - High Fluoride/High Iodine = 3.9 mg/L – High Fluoride/Low Iodine = 2.0 mg/L – High Fluoride = 1.8 mg/L – Low Fluoride =  0.38-0.5 mg/L – Control Area = 0.8 mg/L
    Controls for Confounding Factors: (1) Water iodine level used as variable. (2) Child’s pre-school education history was determined. (3) Parent’s literacy was determined.
    Type of IQ Test Bient-Siman
    Results: (A) Children in areas with high-fluoride and low-iodine have significantly lower IQs than children in areas with high-fluoride and high-iodine, p < 0.01. (B) More children have low IQ (< 69) in areas with High F/High I (10.53%), High F only (7.32%), and High F/Low I (12.82%) than in control group (1.61%)
    Conclusion: “The number of children whose level of intelligence is lower is significantly increased in regions of high fluoride/iodine, regions of high fluoride only, regions of high fluoride/low iodine, against their respective comparative groups. . . . This could be demonstrative of the fact that fluoride acts to increase the toxicity and worsen the occurrence of thyroid swelling.”
     IQ Study #9: Li (1994)
    Citation: Li Y, et al. (1994). Effects of high fluoride intake on child mental work capacity: Preliminary investigation into the mechanisms involved. Journal of West China University of Medical Sciences 25(2):188-91 (republished in Fluoride 2008; 41:331-35).
    Location of study: Sichuan Province, China
    Size of study: 158 children from two neighboring townships (107 children with various degrees of dental fluorosis; 51 children with no dental fluorosis)
    Age of Subjects: 12-13 years old
    Source of Fluoride Exposure: Food contaminated by coal smoke
    Fluoride Content of Grain: - Children with no dental fluorosis = 0.5 mg/kg- Children with dental fluorosis (HiF1) = 4.7 mg/kg- Children with dental fluorosis (HiF2) = 5.2 mg/kg- Children with dental fluorosis (HiF3) = 31.6 mg/kg
    Controls for Confounding Factors: (1) The areas have similar levels of fluoride in water (0.3 mg/L) and air (0.02-0.51 mg/m3) and similar levels of zinc in soil. (2) The areas townships have similar economic and cultural status, lifestyle, dietary habits, basic constituents of food. (3) Age, gender, and grade level of the children are kept “as constant as possible.” (4) Children with acute or chronic diseases not related to fluoride were excluded from study.
    Type of IQ Test Mental Work Capacity determined by number of letters found (NLF), rate of error (RE), index of mental capacity (IMC), short-term memory capacity (SMC), visual reaction time (RT).
    Results: (A) Children with dental fluorosis in mid-exposure group (HiF2) have reduced short-term mental capacity (p<0.05), reduced mental capacity index (p < 0.01), and reduced NLF scores (p<0.01) as compared to children with no fluorosis and children with lower exposure.(B) Children with dental fluorosis in high-exposure group (HiF3) have reduced short-term mental capacity (p<0.01), reduced mental capacity index (p < 0.01), and reduced NLF scores (p<0.01) as compared children with no fluorosis and children with low exposure.
    Conclusion: “As shown in this study, the mental work capacity (MWC) of the two groups of children with grade 3 dental fluorosis was lower than the two groups with no dental fluorosis. . . . This indicates that early, long-term exposure to excess fluoride causes deficits in memory, attention, and reaction time, but 12–13 year-old children with only recent exposure show no major effects. Studies [on human fetuses] have already shown that the developing brain is one of the ripest targets for disruption by fluoride poisoning. Given that before six years of age the human brain is in its fastest stage of development, and that around seven and eight basic structural development is completed, therefore the brain is most vulnerable to damage from excess fluoride intake before this age.”
     IQ Study #8: Yang (1994)
    Citation: Yang Y, et al. (1994). The effects of high levels of fluoride and iodine on intellectual ability and the metabolism of fluoride and iodine. Chinese Journal of Epidemiology 15(4):296-98 (republished in Fluoride 2008; 41:336-339).
    Location of study: Shandong Province, China
    Size of study: 60 children (30 from high-F village, 30 from Low-F village)
    Age of Subjects: 8-14 years old
    Source of Fluoride Exposure: Water
    Water Fluoride Levels: High F/High Iodine area = 2.97 mg/L Control area = 0.5 mg/L
    Urine Fluoride Levels: High F/High Iodine area = 2.08+1.03 mg/L Control area = 0.82+0.56 mg/L
    Controls for Confounding Factors: (1) Iodine exposure. (2) Areas are in close proximity to each other.
    Type of IQ Test Chinese Comparative Scale of Intelligence Test
    Results: (A) Children in high F/high iodine area have lower IQ (76.67+7.75) than those in low F area (81.67+11.97), although the difference is not statistically significant.(B) Greater percentage of children have moderately low IQ (<79) in High F/High Iodine area (76.67%) than in control area (36.67%), p<0.01.
    Conclusion:  “An excess of fluoride and a lack of iodine in the same environment has been shown to have a marked effect on child intellectual development, causing a more significant intellectual deficit than lack of iodine alone.”
     IQ Study #7: An (1992)
    Citation: An J, et al. (1992). The effects of high fluoride on the level of intelligence of primary and secondary students. Chinese Journal of Control of Endemic Diseases 7(2):93-94.
    Location of study: Xingshunxi Town, Guyang County, Inner Mongolia (4 neighboring villages with high fluoride centered around Wubu Ziyao village and 6 neighboring villages with lower fluoride centered around Hada Heshao Village).
    Size of study: 242 children (121 children from high-F villages and 121 children from the low-F villages)
    Age of Subjects: 7-16 years old
    Source of Fluoride Exposure: Water
    Water Fluoride Levels: High-F villages = 2.1+7.6 mg/L Control villages = 0.6+1.0 mg/L
    Controls for Confounding Factors: (1) Dental fluorosis rates were determined in both areas (90.9% in High-F area vs. 21.5% in Low-F area). (B) Both areas are in the countryside, are 15 km from each other, and share the same Han ethnicity. (C) The geography, culture, education, living standard, and social economic conditions are “very similar.”
    IQ Test: Wechsler Intelligence Scale for Children
    Results: (A) Children in the High-F villages have significantly lower IQs at each age group studied: 7-10 (p < 0.02); 11-13 (p < 0.01); 14-16 (p < 0.03); 7-16 (p < 0.01). (B) Significantly more children in High-F villages have “critical state” IQ, p < 0.01. (C) When children within the High-F villages are stratified into highest-F (5.2-7.6 mg/L), and lowest-F levels (2.1-3.2 mg/L), the children in the higher-F areas had significantly lower IQ than the lower-F areas (p < 0.05).
    Conclusion “The results show that the level of intelligence of primary and secondary students from the high fluoride area and that of primary and secondary students from the non-high fluoride area had very significant differences, proving that high fluoride has adverse effects on the mental development of students. The higher the water fluoride is, the lower the level of IQ.”
     IQ Study #6: Lin (1991)
    Citation: Lin Fa-Fu; et al (1991). The relationship of a low-iodine and high-fluoride environment to subclinical cretinism in Xinjiang. Endemic Disease Bulletin 6(2):62-67 (republished in Iodine Deficiency Disorder Newsletter Vol. 7(3):24-25).
    Location of study: Hetian prefecture, Xinjiang, China
    Size of study: 749 children (250 children in High-F/Low Iodine area; 256 children in Low-F/Low-Iodine area; and 243 children in Low F/Low Iodine area)
    Age of Subjects: 7-14 years old
    Source of Fluoride Exposure: Water
    Water Fluoride Levels: High F/Low Iodine = 0.88 mg/L Low F/Low Iodine = 0.34 mg/L Control area = n/a
    Urine Fluoride Levels: High F/Low Iodine = 2.56 mg/L Low F/Low Iodine = 1.34-1.61 mg/L Control area = 1.6 mg/L
    Controls for Confounding Factors: (1) Iodine exposure. (2) Lower socioeconomic status in all areas. (3) Areas have similar nationalities, habits, customs, and income.
    IQ Test: CRT-RC (Combined Raven’s Test for Rural China)
    Results: Children from the High F/Low Iodine area have significantly lower IQs (IQ=71) than children from the Low F/Low Iodine area (IQ=77-79; p<0.05), and control area (IQ=96); p<0.01).
    Conclusion: “The significant differences in IQ among these regions suggests that fluoride can exacerbate central nervous lesions and somatic developmental disturbance caused by iodine deficiency.”
     IQ Study #5: Guo (1991)
    Citation: Guo X, et al. (1991). A preliminary investigation of the IQs of 7-13 year old children from an area with coal burning-related fluoride poisoning. Chinese Journal of Endemiology 10(2):98-100 (republished in Fluoride 2008; 41(2):125–28).
    Location of study: Xinshao County, Hunan Province, China
    Size of study: 121 children (60 children with mild to severe fluorosis from an endemic area where coal is used as a fuel source; 61 children from a non-endemic area where wood is used as a fuel source)
    Age of Subjects: 7 to 13 years old
    Source of Fluoride Exposure: Coal burning (Fluoride levels in water < 0.5 mg/l in both areas)
    Blood Fluoride Levels: Endemic area=0.1483+0.0473 mg/L Non-endemic area=0.1044+0.0652 mg/L (p<0.01)
    Controls for Confounding Factors: The two areas are neighboring townships with “very similar” economies, cultures, living standards, lifestyles, public health, and education.
    IQ Test: Chinese Binet IQ Test
    Results: (A) Children from endemic fluorosis area have lower average IQ (76.7) than children in non-endemic area (81.4), p<0.05. (B) A greater percentage (30%) of children in endemic area have low IQ (<69) than in non-endemic area (11.5%), p<0.05.
    Conclusion:  ”In summary, although diminished intellectual ability can result from a multitude of factors (both innate and acquired) that influence neural development and cell division in the cerebrum, the comparison conducted in this study of two areas where the other environment factors are basically the same shows clear differences in IQ, and it [is] probable that this difference is due to a high fluoride environment.”
     IQ Study #4: Chen (1991)
    Citation: Chen YX, et al. (1991). Research on the intellectual development of children in high fluoride areas. Chinese Journal of Control of Endemic Diseases 6(Suppl):99-100 (republished in Fluoride 2008; 41:120–24).
    Location of study: Linyi County, Shanxi Province, China
    Size of study: 640 children (320 children from High-F village; 320 children from Lower-F village)
    Age of Subjects: 7 to 14 years old
    Source of Fluoride Exposure: Water
    Water Fluoride Levels: High-F village = 4.55 mg/L Lower-F village = 0.89 mg/L
    Controls for Confounding Factors: The occupations, culture, standard of living, lifestyle habits, access to health and transportation facilities are “essentially the same” between the two areas.
    IQ Test: Rural version of Chinese Standardized Raven Test
    Results: Average IQ of children in High-F village (100.24+14.52) significantly lower than children in lower-F village (104.03+14.96), p<0.01.
    Conclusion: “The results of this study indicate that there is significant difference between the intellectual ability of the 7–14 year old children from the [fluorosis] endemic area and those of the control, and moreover that the average IQ of the children from the endemic area is clearly lower.”
     IQ Study #3: Sun (1991)
    Citation: Sun M, et al. (1991). Measurement of intelligence by drawing test among the children in the endemic area of Al-F combined toxicosis. Journal of Guiyang Medical College 16(3):204-06.
    Location of study: Guizhou Province, China: Liupanshui City (endemic fluorosis area) and Guiyang City (non-endemic area)
    Size of study: 420 children (196 children from endemic fluorosis area; 224 children from non-endemic area)
    Age of Subjects: 6.5-12 years old
    Source of Fluoride Exposure: N/A
    Fluoride exposure levels: N/A
    Controls for confounding factors: (1) Majority of children of farmers. (2) Children with bone and joint deformities or nervous system symptoms were excluded from study.
    IQ Test: Drawing test for children (Japanese researcher’s Shigeo Kobayashi’s 50-point scoring method).
    Results: Children from endemic fluorosis area had lower IQ than those from non-endemic area at all ages except <7 (p < 0.05)
    Excerpt:  ”From these results, it can be concluded that excessive consumption of fluorine and aluminum in the early stage of development directly impacts the development of the human brain, which causes the delayed intellectual development seen in children living in the endemic areas.”
     IQ Study #2: Qin (1990)
    Citation: Qin LS, Cui SY. (1990). Using the Raven’s standard progressive matrices to determine the effects of the level of fluoride in drinking water on the intellectual ability of school-age children. Chinese Journal of the Control of Endemic Diseases 5(4):203-04 (republished in Fluoride 2008; 41:115–19).
    Location of study: Jing County, Hubei Province, China
    Size of study: 447 children (141 children from High-F area; 159 children from “normal” F area; 147 children from low-F area)
    Age of Subjects: 9 to 10.5 years old
    Source of Fluoride Exposure: Water
    Water Fluoride Levels: High F = 2.1-4.0 mg/L“Normal” F = 0.5-1.0 mg/LLow F = 0.1-0.2 mg/L
    Controls for confounding factors: All children had grown up drinking well water in their home village.
    IQ Test: Raven’s Standard Progressive Matrices
    Results: Children in High F (21.17%) and Low F (23.03%) areas had lower average IQ scores than children in normal F area (28.14%), p<0.01.
    Conclusion: “All of these finding serve to indicate that both high and low fluoride can affect the normal development and function of the cerebrum as well as the entire nervous system causing a decrease in intellectual ability.”
    IQ Study #1: Ren (1989)
    Citation: Ren D, et al. (1989). A study of the intellectual ability of 8-14 year-old children in high fluoride, low iodine areas. Chinese Journal of Control of Endemic Diseases 4(4):251 (republished in Fluoride 2008; 41:319-20).
    Location of study: Shandong Province, China
    Size of study: 329 children (160 children in High F/low Iodine area: 169 children in Low-F/Low Iodine area)
    Age of Subjects: 8 to 14 years old
    Source of Fluoride Exposure: Water
    Fluoride exposure levels: N/A
    Controls for confounding factors: Both study groups had low iodine intake.
    IQ Test: Wechsler Intelligence Test
    Results: - Average IQ of children in the High Fluoride/Low Iodine group (IQ=64.8) significantly lower than the children in the Low Fluoride/Low Iodine group (IQ = 85.0), p<0.01.- The percentage of children with low IQ (<69) significantly greater in High F/Low Iodine group (40.6%) than in Low Fluoride/Low Iodine  group (13.6%), p<0.01.
    Conclusion: “From the results it is evident that disrupted child intellectual development is among the effects on the human body from a harmful environment containing both high fluoride and low iodine, and this disruption is clearly much more serious than the effects of iodine deficiency alone.”