Research Studies
Study Tracker
Part 2. IQ-Studies Reporting “No Effect”; and one study that shows a large increase in IQ.Abstract
Part 2. IQ-Studies Reporting “No Effect”; and one study that shows a large increase in IQ (1989-2025)
The following 12 studies are based on IQ/cognitive examinations of 5,841 children and 942 adults. Out of the 12 studies, 11 did not find an association between exposure to fluoride and lowered IQ. One study by Ibarluzea et al. (2021) found an increase of 15 IQ points for boys living in fluoridated communities.
See Part 1 for a list of 87 IQ studies reporting lowered IQ from fluoride exposure.
| # | YEAR | AUTHOR – STUDY – JOURNAL | COUNTRY | # CHILDREN |
| 12 | 2025 | Do et al. Early Childhood Exposures to Fluorides and Cognitive Neurodevelopment: A Population-Based Longitudinal Study. Journal of Dental Research |
Australia | 357 participants
16 – 26 years old |
| Abstract: …The sample was selected from the National Child Oral Health Study (NCOHS) 2012–2014. NCOHS collected data on socioeconomic factors, oral health behaviors, and residential history to estimate percentage lifetime exposure to fluoridated water during the first 5 y of life (%LEFW). NCOHS children were also examined by trained and calibrated examiners to assess dental fluorosis (a reliable and valid individual biomarker of total fluoride intake during early childhood). The sample was followed up in 2022–2023 to collect data on cognitive neurodevelopment (intelligence quotient [IQ]) using the WAIS-IV, which was administered by trained and calibrated qualified psychologists. Multivariable regression models were generated to investigate associations between the 2 exposure measurements (%LEFW and dental fluorosis) with full-scale IQ (FSIQ) scores, controlling for important confounding effects. …Conclusion: This population-based follow-up study has provided consistent scientific evidence that early-life exposure to fluoride was not negatively associated with cognitive neurodevelopment. The findings, in combination with the current body of knowledge, provide assurance that the currently practiced WF [water fluoridation] programs are both effective and safe for young children. | ||||
| 11 | 2023 | Lin et al. Association of Dental Fluorosis and Urinary Fluoride with Intelligence among Schoolchildren. Children |
Taiwan | 562 children
6 – 12 years |
| Abstract: …This study aimed to assess the relationship between urinary fluoride, dental fluorosis, and intelligence among schoolchildren living in communities with non-fluoridated drinking water. This cross-sectional study was conducted on 562 children aged 6–12 years in Taichung, Taiwan. Each child’s urinary fluoride level was determined by a fluoride-ion-selective electrode, and the dental fluorosis condition was evaluated according to the criteria of Dean’s Index. The Raven’s Colored Progressive Matrices-Parallel and Standard Progressive Matrices-Parallel were used to assess children’s intelligence. The results showed that the mean (±standard deviation) urinary fluoride concentrations were 0.40 ± 0.27 mg/L (0.43 ± 0.23 mg/g creatinine) among participants. The prevalence of dental fluorosis was 23.67%. After extensive evaluation of potential confounders, dental fluorosis and urinary fluoride were not associated with intelligence quotient (IQ) scores or grades in the regression models. In conclusion, dental fluorosis and urinary fluoride levels were not significantly related to the IQ of schoolchildren living in areas with low drinking water fluoride. | ||||
| 10 | 2021 | Ibarluzea et al. Prenatal exposure to fluoride and neuropsychlogical development in early childhood: 1-to4 years old children. Environmental Research |
Spain | 316 to 248 mother-child pairs
1 – 4 years of age |
| Results: No association was found between MUFcr [maternal urinary Fluoride adjusted by creatinine] levels and Bayley Mental Development Index score. Nevertheless, regarding the McCarthy scales, it was found that per unit (mg/g) of MUFcr across the whole pregnancy, scores in boys were greater for the verbal, performance, numeric and memory domains (B = 13.86, CI 95%: 3.91, 23.82), (B = 5.86, CI 95%: 0.32, 11.39), (B = 6.22, CI 95%: 0.65, 11.79) and (B = 11.63, CI 95%: 2.62, 20.63) respectively and for General Cognitive Index (B = 15.4, CI 95%: 6.32, 24.48). For girls there was not any cognitive score significantly associated with MUFcr, being the sex-F interactions significant (P interaction <0.05). Including other toxicants levels, quality of family context or deprivation index did not substantially change the results. ________________________________________ Comment from FAN: The study found an increase of 15 IQ points for boys living in fluoridated communities. It differs significantly from other observations. |
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| 9 | 2019 | Soto-Barreras et al. Effect of fluoride in drinking water on dental caries and IQ in children. Fluoride |
Mexico | 161 children
9 to 10 years of age |
| Water fluoride level: 39% of the drinking water samples were above 1.5 mg/L. In addition, almost 50% of the study population referred to tap water as being their main source of consumption. Results: No relationship was found between intellectual ability and fluoride exposure variables such as, dental fluorosis, levels of fluoride in drinking water and urine, and exposure dose. Conclusions: In conclusion, our results suggest that fluoride exposure above 1.0 mg/L in drinking water acts as a protective factor against dental caries. No evidence was found for fluoride-associated cognitive deficits… further research is needed to clarify whether or not fluoride may possibly have adverse effects on brain development. |
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| 8 | 2018 | Sharma et al. Does fluorosis affect the intelligence profile of children? A cross sectional analysis of school children of district Una, Himachal Pradesh, India. International Journal of Community Medicine and Public Health |
India | 600 children
10 – 14 years old |
| Results: The 60% of sites studied for fluoride levels were found to have >0.5 ppm fluoride level in water and none of them with level more than 1 ppm. Prevalence of dental fluorosis was 12.2%. Dental caries and high Dental Aesthetic Index were positively associated with high fluoride level in water. Low intelligence level of adolescents was not significantly associated with high fluoride level (OR;95% CI: 1.34; 0.72-2.49). Conclusions: This sub Himalayan region is not endemic for fluorosis however lower level of fluoride is observed in many sites. Fluorosis was not significantly associated with intelligence hence indicating towards multifactorial causation of disease. |
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| 7 | 2015 | Broadbent et al. Community water fluoridation and intelligence: prospective study in New Zealand. American Journal of Public Health 105(1):72-76. |
New Zealand | 1973: 992 children 2010: Children aged 7 to 13 years This review: 38 years later |
| Objectives: This study aimed to clarify the relationship between community water fluoridation (CWF) and IQ. Methods: We conducted a prospective study of a general population sample of those born in Dunedin, New Zealand, between April 1, 1972, and March 30, 1973 (95.4% retention of cohort after 38 years of prospective follow-up). Residence in a CWF area, use of fluoride dentifrice and intake of 0.5-milligram fluoride tablets were assessed in early life (prior to age 5 years); we assessed IQ repeatedly between ages 7 to 13 years and at age 38 years. Results: No significant differences in IQ because of fluoride exposure were noted. These findings held after adjusting for potential confounding variables, including sex, socioeconomic status, breastfeeding, and birth weight (as well as educational attainment for adult IQ outcomes). Conclusions: These findings do not support the assertion that fluoride in the context of CWF programs is neurotoxic. Associations between very high fluoride exposure and low IQ reported in previous studies may have been affected by confounding, particularly by urban or rural status. This review was partly funded by: U.S. National Institute of Dental and Craniofacial Research Grant R01 DE-015260-01A1, UK Medical Research Council Grant MR/K00381X/1 ___________________________________ Comment from FAN: The study reports no association between fluoridation and IQ. As recognized by Dr. Philippe Grandjean, there are several glaring problems with this study, however, including the fact that virtually all of the children in the “non-fluoridated” community used fluoride supplements (a prescription drug designed to deliver the same amount of fluoride a child would get from drinking fluoridated water). |
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| 6 | 2011 | Kang et al. Effects of fluoride and arsenic in drinking water on children’s intelligence. Chinese Journal of School Health 32(6):679-81. [Chinese abstract in English; text in Chinese] |
Inner Mongolia |
268 children |
| Objective: To study the effect of fluoride and arsenic exposure in drinking water on children’s intelligence ,and to provide scientific basis for children’s health protection. Methods: Two hundred and sixty-eight pupils in Hangjinhou Qi, Inner Mongolia were selected as subjects. Fluoride and arsenic in drinking water were determined. The Chinese combined Raven’s Test was applied to evaluate the intelligence of children. In addition, the questionnaire survey was conducted to find out information including general information of households, source of drinking water, health of subjects and intelligence-related factors. Results: The average concentrations of fluoride and arsenic in drinking water were (1.24±0.74) mg/L and (0.13±0.16) mg/L, which were higher than limits of national standard. The intelligence quotient (95.9±14.2) of girls exposed to arsenic >0.05 mg/L in drinking water was lower than IQ of girls (101.3±13.2) exposed to low level arsenic (<0.05 mg/L). IQ of boys had not been observed significant difference between high and low level of arsenic exposure. Adjusted OR of effect of arsenic on girls’ IQ was 2.81. On the other hand, IQs of children exposed to high and low level of fluoride in drinking water showed no significant difference. Conclusion: Children’s exposure to arsenic of high concentration in drinking water probably has adverse effects on their intelligence development in some degree. Girls’ IQ seem more susceptible to arsenic. |
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| 5 | 2010 | Li X et al. Investigation and Analysis of Children’s IQ and Dental Fluorosis in a High Fluoride Area. Chinese Journal of Pest Control 26(3):230-31. Translated from Chinese to English by FAN, [Chinese text |
China | 676 children
7 – 10 years old |
| Water fluoride level: The content of fluoride in the drinking water was 2.47 ±0.75mg/L. Dental fluorosis and intelligence quotients (IQ) were determined in 374 males and 302 females. In total, 347 were diagnosed as having dental fluorosis, producing a prevalence rate of 51.33%. Results: The average IQ among the children in the high fluoride area was 98.06 and the rate of mental retardation was 5.47%. Intelligence distribution in the children with and without dental fluorosis did not show any difference, and no sex-specific differences in intelligence were found. The area does not have a deficiency of iodine and there is no known pollution source. Conclusions: The long-term consumption of high fluoride water may adversely affect children’s intellectual development. ________________________________________ Comment from FAN: The study did not compare a high fluoride area against a low-fluoride area. Instead, it compared the IQs of children with dental fluorosis in a high-fluoride area with the IQs of children without dental fluorosis in the same high-fluoride area. |
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| 4 | 2010 | He et al. Investigation of children’s intelligence quotient and dental fluorosis in drinking water-type of endemic fluorosis area in Pucheng county Shaanxi province before and after drinking water change. Chinese Journal of Epidemiology 29:547-48 |
China | 200 children
8 – 12 years old |
| Source of fluoride: Water from endemic fluorosis area and non-endemic area. Results: The rates of child dental fluorosis in changed water and unchanged water endemic fluorosis areas were 28. 50% (57/200), 87.88% (203/231), respectively, the difference was statistically significant (x2=159.19, P <0.01), while dental fluorosis indices were 0.57, 1.97, was marginal, moderate epidemic. Children with IQ above 90 was accounted for 89.5% (179/200), 91.5% (183/200) in changed water and unchanged water endemic fluorosis area. Conclusions: Changed water may decrease the incidence of child dental fluorosis, but has no obvious effect on children’s IQ development in endemic fluorosis area. |
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| 3 | 2000 | Calderon et al. Influence of fluoride exposure on reaction time and visuospatial organization in children. Epidemiology 11(4): S153. |
Mexico | 61 children
6 – 8 years old |
| Results: Mean value of fluoride in urine was 4.3 mgF/g creatinine (1.6–10.8). Mean PbB value was 6.2 ug/dl(2.0–15.6). After controlling by significant confounders, urinary fluoride correlated positively with reaction time and inversely with the scores in visuospatial organization. IQ scores were not influenced by fluoride exposure. Conclusions: An increase in reaction time could affect the attention process, also the low scores in visuospatial organization could be affecting the reading and writing abilities in these children. _____________________________________________ Comment from FAN: The study found that fluoride exposure was associated with other indices of neurotoxicity, including impaired visual-spatial organization. This is a conference abstract from the 2000 Annual Conference of the ISEE (International Society for Environmental Epidemiology). No full study has been published. |
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| 2 | 1998 | Spittle et al. Intelligence and fluoride exposure in New Zealand Children. (abstract | New Zealand | 1265 children born in 1977
8 – 9 years old |
| Water Fluoride Level: half of the participants resided in Waimairi County, fluoridated with 1 ppm of fluoride, while the other half resided in non-fluoridated Christchurch with 0.1 ppm. Results: The mean IQs (WISC-R) at 8 years for these groups were 100.0, 99.04, 99.40 and 100.5 (p>0.30). The values at 9 years were 99.9, 99.3, 98.7 and 101.2 (p>0.70). Conclusions: There was no trend for IQ to decline with increasing exposure to fluoridated water. In fact those who lived for 7 years in an area with fluoridated water had the highest mean IQ scores, although this difference was not statistically significant. _____________________________________________ Comment from FAN: This study made no attempt to ascertain the urinary fluoride levels of the children. This is particularly important to do in studies of western populations because there is now a great deal of overlap in fluoride exposures between children living in fluoridated vs. non-fluoridated communities. Thus, any IQ study of western populations that does not include a measurement of individual fluoride exposure will be unlikely to find an association between fluoride and IQ. |
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| 1 | 1989 | Hu et al. Research on the Intellectual Ability of 6-14 Year Old Students in an Area with Endemic Fluoride Poisoning. Collection of papers and abstracts of 4th China Fluoride Research Association. 6:73. Translated from Chinese to English by Fluoride Action Network [Chinese text] |
China | 383 children |
| Size of study: This study investigated the IQs of 379 students in total, including 198 students from the endemic region with IQs ranging from 68 to 105 and average IQ of 85.15 as well as 181 students for the non-endemic region with IQs ranging from 60 to 107 and an average IQ of 84.90, (t = 0.79, p>0.05). Water Fluoride Level: The endemic area has a fluoride content of 7.00 ppm; the neighboring areas show no sign of fluoride poisoning, each having less than 0.8 ppm of fluoride in their water. Results: – there were no significant statistical differences due to age or gender – both areas show only average or below average IQs, with 28.29% and 29.28% of children in the “low” category in the endemic and non-endemic regions, respectively, and there was no “excellent” students in either area; even the 100-110 range had only 5.10% and 6.63% of students within that range, respectively. – The IQs of adults from the areas were also measured, and the intellectual ability and even the life expectancy of people from the endemic region appeared to be higher than the non-endemic region, indicating that the effect of fluoride poisoning on intellectual ability is negligible. Conclusions: “this region is economically and culturally underdeveloped with life here difficult, and the results suggest that the intellectual development of all the children studied is poor… These results suggest nutritional deficits and social, economic, and cultural underdevelopment are the primary factors in low intellectual ability seen in both the subjects and the control, but further research should be done to determine if the excess zinc or manganese found in grains consumed in the region may also be playing a role.” |
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