Fluoride Action Network

Fluoride & IQ: The 7 “No Effect” Studies

Fluoride Action Network | by Michael Connett | Updated 2018

While 53 studies have found an association between fluoride and IQ, the following seven studies did not find this association. Several points bear consideration about these studies:

First, a new study from New Zealand (Broadbent 2014) 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.

Second, the study by Calderon (2000) found that fluoride exposure was associated with other indices of neurotoxicity, including impaired visual-spatial organization.

Third, 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.

Fourth, 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.

Seven Studies finding no association between fluoride and IQ:

IQ Study #7: (Broadbent, 2015)

Citation: Broadbent JM, Thomson WM, Ramrakha S, Moffitt TE, Zeng J, Foster Page LA, Poulton R. 2015. Community water fluoridation and intelligence: prospective study in New Zealand. 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. 2011. Effects of fluoride and arsenic in drinking water on children’s intelligence. 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. 2010. Investigation and Analysis of Children’s IQ and Dental Fluorosis in a High Fluoride AreaChinese 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.

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.

IQ Study # 4: (He, 2010)

Citation: He M, Zhang C. 2010. 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. [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. 2000. Influence of fluoride exposure on reaction time and visuospatial organization in children. 2000. Epidemiology 11(4): S153.
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. 1998. Intelligence and fluoride exposure in New Zealand Children (abstract). Fluoride 31:S13.
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. 1989. 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 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
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.”