Limitations of 2011 Choi and Grandjean meta-analysis
The “reduced IQ studies” are a reference to a 2011 review of 27 Chinese studies found in obscure Chinese journals by researchers Phillippe Grandjean and Anna Choi. These studies were of the effects of high levels of fluoride (as high as 11.5 ppm) in the well-water of various Chinese, Mongolian, and Iranian villages.
By the admission of Grandjean and Choi, themselves, these studies had key information missing, inadequate control for confounders, and questionable methodologies. These 27 studies were so seriously flawed that Grandjean and Choi were led to issue a public statement in March, 2012 that the studies should not be used to judge water fluoridation in the US. This obviously has not stopped fluoridation opponents from doing so anyway.
“These results do not allow us to make any judgment regarding possible levels of risk at levels of exposure typical for water fluoridation in the U.S. On the other hand, neither can it be concluded that no risk is present. We therefore recommend further research to clarify what role fluoride exposure levels may play in possible adverse effects on brain development, so that future risk assessments can properly take into regard this possible hazard.”
–Anna Choi, research scientist in the Department of Environmental Health at HSPH, lead author, and Philippe Grandjean, adjunct professor of environmental health at HSPH, senior author.
Limitations of Bashash, et al. Mexican study
1. The recent Bashash, et al., Mexican study is of the effects on children, of prenatal fluoride exposure to pregnant moms. Unlike the authors of this study, Fluoridation opponents citing this study omit its stringent limitations, as are clearly stated in the study itself. These limitations include:
A. A lack of data on urinary fluoride content of pregnant women living in fluoridated areas of the United States. Fluoridation opponents seek to do what the authors, themselves, did not do….compare urinary fluoride content of one population with non-existent data of another.
“Finally, our ability to extrapolate our results to how exposures may impact on the general population is limited given the lack of data on fluoride pharmacokinetics during pregnancy. There are no reference values for urinary fluoride in pregnant women in the United States” (1)
B. Insufficient information to rule out significant confounders.
“Nevertheless, it is not possible to entirely rule out residual confounding or in the population as a whole (that might have been detected had we had full data on larger sample sizes) or bias (should the subpopulations that had the data for analysis have a different fluoride–cognition relationship than those participants who were excluded from the analyses).”
C. There was no significant effect noted by fluoride exposure on children after birth.
“Finally, in models that focused on the cross-sectional relationship between children’s exposure to fluoride (reflected by their specific gravity–adjusted urinary fluoride levels) and IQ score and that contained the main covariates of interest, there was not a clear, statistically significant association between contemporaneous children’s urinary fluoride (CUFsg) and IQ either unadjusted or adjusting for MUFcr.” (1)
D. Evidence suggested that IQ effects were noted only with prenatal urinary content above 0.8 mg/L.
“The associations with GCI appeared to be linear across the range of prenatal exposures, but there was some evidence that associations with IQ may have been limited to exposures above 0.8 mg/L.” (1)
E. Results would need to be replicated by independent researchers.
“Our findings must be confirmed in other study populations, and additional research is needed to determine how the urine fluoride concentrations measured in our study population are related to fluoride exposures resulting from both intentional supplementation and environmental contamination.” (1)
F. “Other limitations include the lack of information about iodine in salt, which could modify associations between fluoride and cognition; the lack of data on fluoride content in water given that determination of fluoride content is not reported as part of the water quality monitoring programs in Mexico; and the lack of information on other environmental neurotoxicants such as arsenic.” (1)
G. Bashash, et al., utilized the “spot” collection method of urine collection, rater than the more
accurate 24 hour method.
As noted by Deena Thomas, second author of Bashash, et al:
“The spot urine samples we measured cannot account for diurnal variations in urinary fluoride. Previous studies report fluctuations in concentration by time-of-day42 which means that the fluoride levels in our samples could be influenced by the time-of-collection or by diet.”
Additionally, in her doctoral thesis, Deena Thomas, using the exact data as did Bashash, reported on the effects of prenatal fluoride on children aged 1, 2, and 3. She found no significant effect on these children. Bashash, chose to omit these findings, and instead began their IQ assessment in children 4 years of age.
Obviously, Bashash, et al. had the same data as did Thomas, so why did they omit any reference to children below the age of 4? (2)
From Thomas’ dissertation
“Conclusions: This analysis suggests that maternal intake of fluoride during pregnancy does not have a strong impact on offspring cognitive development in the first three years of life.” 2
(1) Prenatal Fluoride Exposure and Cognitive Outcomes in Children at 4 and 6–12 Years of Age in Mexico
Bashash, Thomas, et al.
Environ Health Perspect; DOI:
(2) Fluoride exposure during pregnancy and its effects on childhood neurobehavior: a study among mother-child pairs from Mexico City, Mexico
University of Michigan 2014