While 74 studies have found an association between fluoride and IQ, the following eight studies did not find this association. The 74 studies were based on IQ/cognitive examinations of 27,174 children (71 studies) and 689 adults (3 studies).
The following 9 studies,which did not find an association between exposure to fluoride and lowered IQ, included 4,363 children and 1,037 adults.
We will soon provide comments on the Spanish 2021 study by Ibarluzea et al. This study found an increase of 15 IQ points for boys living in fluoridated communities.
The study from New Zealand (Broadbent 2015) 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). FAN discusses these problems here.
The study by Calderon (2000) found that fluoride exposure was associated with other indices of neurotoxicity, including impaired visual-spatial organization.
The study by Li (2010) 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.
Lastly, the study by Spittle (1998) of a fluoridated community in New Zealand 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. This overlap in exposure is due to several facts including: (1) frequent prescription of fluoride supplements to children in non-fluoridated areas; (2) ingestion of large amounts of fluoride toothpaste; (3) exposure to fluoridated water through processed foods and beverages; (4) exposure to fluoride through pesticides; and (5) exposure to fluoride from Teflon. 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.
NINE Studies finding no association between fluoride and IQ:
IQ Study #9: (Ibarluzea – 2021)
|Ibarluzea J, Gallastegi M, Santa-Marina L, Jiménez Zabala A, Arranz E, Molinuevo A, Lopez-Espinosa MJ, Ballester F, Villanueva CM, Riano I, Sunyer J, Tardon A, Lertxundi A. Environmental Research, October.|
|Location of Study:||Gipuzkoa, Spain -the Infancia y Medio Ambiente (Childhood and Environment, INMA) birth cohort|
|Size of Study:||316 to 248 mother-child pairs|
|Age of Subjects:||1 – 4 years of age|
|Source of Fluoride:||Drinking Water.|
|Water Fluoride Level:||According to the authors: “From the food and drink questionnaires administered during pregnancy, we identified the ten most consumed BW [bottled water] brands and then ascertained that F levels in these brands ranged from 0.07 to 0.48 mg/L.”|
|Type of IQ Test:||Bayley Scales (age of 1) and the McCarthy Scales (age of 4).|
“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 (? = 13.86, CI 95%: 3.91, 23.82), (? = 5.86, CI 95%: 0.32, 11.39), (? = 6.22, CI 95%: 0.65, 11.79) and (? = 11.63, CI 95%: 2.62, 20.63) respectively and for General Cognitive Index (? = 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.”
|Conclusions:||“In boys, positive associations were observed between MUFcr and scores in cognitive domains at the age of 4. These findings are inconsistent with those from some previous studies and indicate the need for other population-based studies to confirm or overturn these results at low levels of F in CDW.”|
IQ Study #8: (Soto-Barreras – 2019)
|Soto-Barreras U, Escalante-Villalobos KY, Holguín-Loya B, Perez-Aguirre B, Nevárez-Rascón A, Martínez-Martínez RE, Loyola-Rodríguez JP. Fluoride 52(3 Pt 3):474-482.|
|Location of Study:||Chihuahua, Mexico|
|Size of Study:||161 children|
|Age of Subjects:||9 to 10 years of age|
|Source of Fluoride:||Water|
|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.|
|Type of IQ Test:||Raven’s Colored Progressive Matrices (RCPM)|
|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.|
IQ Study #7: (Broadbent, 2015)
|Citation:||Broadbent JM, Thomson WM, Ramrakha S, Moffitt TE, Zeng J, Foster Page LA, Poulton R. American Journal of Public Health 105(1):72-76. [Published ahead of print on May 15, 2014].|
|Location of Study:||Dunedin, New Zealand|
|Size of Study:||Prospective study of a general population sample of those born in Dunedin, NZ, between April 1, 1972, and March 30, 1973. Data on IQ were available for 992 and 942 study members in childhood and adulthood, respectively.|
|Age of Subjects:||The cohort of 1037 children (91% of eligible births; 52% boys) was constituted at age 3 years. IQ assessed repeatedly between ages 7 to 13 years and at age 38 years|
|Source of Fluoride:||Water|
|Water Fluoride Level:||0.7 – 1.0 ppm and 0.0 – 0.3 ppm|
|Type of IQ Test:||For children up to 13 years: Wechsler Adult Intelligence Scale-Revised. For adults: Wechsler Adult Intelligence Scale—Fourth Edition (WAIS-IV).|
|Results:||No clear 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 Community Water Fluoridation programs is neurotoxic.|
IQ Study #6: (Kang, 2011)
|Citation:||Kang JQ, Cheng YB, Wu KG. Chinese Journal of School Health 32(6):679-81. [Chinese text]|
|Location of Study:||Hangjinhou Qi, Inner Mongolia|
|Size of Study:||268 students|
|Age of Subjects:||NA|
|Source of Fluoride:||Water|
|Water Fluoride Level:||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.|
|Type of IQ Test:||Chinese combined Raven’s Test. In addition, 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 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.|
|Conclusions:||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.|
IQ Study # 5: (Li, 2010)
|Citation:||Li X, Hou G, Yu B, Yuan C, Liu Y, Zhang L, Hao Z. Chinese Journal of Pest Control 26(3):230-31. [Translated from Chinese to English by FAN] [Chinese text|
|Location of Study:||Primary school in an area with high-fluoride water villages with endemic fluorosis in Kai Feng, Qi County.|
|Size of Study:||676 children|
|Age of Subjects:||7 to 10 years|
|Source of Fluoride:||Water|
|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%.|
|Type of IQ Test:||Chinese combined Raven’s test.|
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.|
IQ Study # 4: (He, 2010)
|Citation:||He M, Zhang C. Chinese Journal of Epidemiology 29:547-48. [Article in Chinese]|
|Location of Study:||Endemic fluorosis area Pucheng County in Shaanxi Provence.|
|Size of Study:||200 children|
|Age of Subjects:||8 to 12 years|
|Source of Fluoride:||Water from endemic fluorosis area and non-endemic area|
|Water Fluoride Level:||NA|
|Type of IQ Test:||Raven’s test|
|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 respectively, the difference was not significant (x2=0.46, P >0.05).|
|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.|
IQ Study # 3: (Calderon, 2000)
|Citation:||Calderon J, Blenda M, Marielena N, Leticia C, Deogracias OM, Diaz-Barriga F. Epidemiology 11(4): S153.
Note: This is a conference abstract from the 2000 Annual Conference of the ISEE (International Society for Environmental Epidemiology). No full study has been published.
|Location of Study:||San Luis Potosi, Mexico|
|Size of Study:||61 children|
|Age of Subjects:||6 to 8 years|
|Source of Fluoride:||Tap water|
|Water Fluoride Level:||1.2 to 3 mg/L.|
|Type of IQ Test:||(1) Wechsler Intelligence Scale for Children Revised version for Mexico (WISC-RM), (2) Rey Osterreith-Complex Figure test and (3) Continuos Performance Test (CPT). Mean value of fluoride.|
|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.|
IQ Study # 2: (Spittle, 1998)
|Citation:||Spittle B, Ferguson D, Bouwer C. Fluoride 31:S13.
1998. Intelligence and fluoride exposure in New Zealand Children (abstract).
|Location of Study:||Christchurch New Zealand|
|Size of Study:||A birth cohort of 1265 children born in 1977|
|Age of Subjects:||8-9 years. The children were grouped according to the duration of fluoridation exposure to age 7 years with the groups being exposed for 0, 1-3, 4-6 and 7 years.|
|Source of Fluoride:||Water|
|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.|
|Type of IQ Test:||Wechsler Intelligence Scale for Children (WISC-R)|
|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.|
IQ Study # 1: (Hu, 1989)
|Citation:||Hu Y, Yu Z. Collection of papers and abstracts of 4th China Fluoride Research Association. 6:73. [Translated from Chinese to English by FAN] [Chinese text]|
|Location of Study:||Hongwu Elementary School, Ankang city, Shaanxi Province|
|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).|
|Age of Subjects:||Elementary school students and adults.|
|Source of Fluoride:||Water|
|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 0.8ppm of fluoride in their water.|
|Type of IQ Test:||Chinese comparative testing|
– 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.
|“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.”|