On 2020-11-08 03:03:45, user perrottk wrote:
Comments on “A Benchmark Dose Analysis for Maternal Pregnancy Urine-Fluoride and IQ in Children”<br />
I question the validity of attempting to determine a BMC for the effect of fluoride intake on IQ without first ascertaining if there is a real effect. The problem of this document is that it assumes an effect without making a proper critical assessment of the evidence for a causal effect.<br />
The draft paper relies completely on two studies which reported very weak relationships from exploratory analyses. Nothing wrong with doing exploratory analyses – providing their limitations are accepted. Such analyses can indicate possibilities for future studies testing possibly causes – but, in themselves, they are not evidence of causation. These studies provide no evidence of causal effect<br />
The studies this draft relies as evidence that fluoride causes a lowering of child IQ illustrates have the following problems.<br />
1: Correlation is not evidence of causation – no matter how good the statistical relationship. And reliance on p-values is not a reliable indicator of the strength of a relationship anyway The two studies relied on here do not report the full results of statical analyses which would have revealed the weaknesses of the relationships.<br />
2: These two studies were exploratory – using existing data. They were not experiments specifically designed to establish a cause.<br />
3: Many other factors besides those investigated can obviously be important in exploratory studies where there is no control of population selection. While authors may claim confounders are considered it is impossible to do this completely – there are so many possible factors to consider. Most are not included in the datasets used and the researchers may make their own selection, anyway.<br />
The study of Malin & Till (2015), referred to in this draft, illustrates the problems. Malin & Till (2015) reported what they considered reasonably strong relationships (p-values below 0.05 and R squared values of 0.21 to 0.34 indicating their relationships explained 21% to 34% of the variance in ADHD prevalence). However, their consideration of possible other risk-modifying factors was limited. They did not include state elevation which Huber et al (2015) showed was correlated with fluoridation. The strength of Huber’s relationship (R squared 0.31 indicating elevation explained 31% of the variance in ADHD prevalence) was similar to that reported by Malin & Till for fluoridation.<br />
Perrott (2018) showed that when elevation is included in the statistical analysis the relationship of ADHD prevalence with fluoridation was non-significant (p>0.05). This show the danger of relying on the results of statistical relationships from exploratory studies where consideration of other possible risk-modifying factors is limited.<br />
4: This draft paper relies on the reported links between cognitive factors and F intake without testing for a causal effect. But it also does not critically assess those correlations. The problems of confounders have already been mentioned but these two studies report very weak relationships or, in most cases, no statistically significant relationships.<br />
For example, of the 10 relationships between measures of fluoride exposure and cognitive effects Green et al (2019) reported that only 4 were statistically significant (Perrott 2020). That is not evidence of a strong relationship and underlines the danger of assuming correlations (especially selected correlations) are evidence of causation. Incidentally, this draft paper mentions the study of Till et al (202) which also reported relationships between fluoride exposure with bottle-fed infants and later cognitive effects. In this case only three of the 12 relationships reported were statistically significant (Perrott 2020).<br />
Even those relationship reported as significant were still very weak. For example Green et al (2015) reported a relationship for boys which explained less than 5% of the variance of IQ measures.
The relationships reported by Bashash et al (2017) were also extremely weak – explaining only about 3.6% of the variance in IQ and 3.3% of the variance in GCI. This weakness is underlined by other reports of relationships found for the Mexican ELEMENT database. Thomas (2014) did not find a significant relationship of MDI with maternal urinary fluoride for children of ages 1 to 3 although in a conference poster paper Thomas et al (2018) reported a statistically significant relationship for urinary fluoride adjusted using creatinine concentrations.<br />
5: As well as ignoring the incidence of non-significant relationships from these studies this draft paper also ignores the findings of positive relationships from other studies. For example, Santa-Marina et al (2019) reported a positive relationship between F intake indicated by maternal urinary F and child cognitive measures. Thomas (2014) also reported a positive relationship of child IQ (MDI for 6 – 15-year-old boys) with child urinary fluoride.<br />
6: The draft paper describes the two studies it uses for its analysis as “robust” but ignores the fact that the findings in these and other relevant studies are contradictory. For example, the findings reported in the two papers differ in that Bashash et al (2017) did not report different effects for boys and girls whereas Green et al (2019) did. Santa-Marina et al (2019) reported opposite effect to those of Bashash et al (2017) and Green et al (2019). These contradictory findings, together with the lack of statistical significance for most of the relationships investigated, are perhaps what we should expect from relationships which are as weak as these are.<br />
Summary<br />
The paper relies on weak relationships from exploratory studies. Such relationships, even where strong, cannot be used as evidence for causation and to assume so can be misleading. BMCs and similar functions derived without any evidence of real effects are not justified. While the derived BMCs may be used by activists campaigning against community water fluoride, they will be misleading for policy makers. This sort of determination of BMC is a least premature and a worst meaningless.<br />
References:<br />
Bashash, M., Thomas, D., Hu, H., Martinez-mier, E. A., Sanchez, B. N., Basu, N., Peterson, K. E., Ettinger, A. S., Wright, R., Zhang, Z., Liu, Y., Schnaas, L., Mercado-garcía, A., Téllez-rojo, M. M., & Hernández-avila, M. (2017). Prenatal Fluoride Exposure and Cognitive Outcomes in Children at 4 and 6 – 12 Years of Age in Mexico. Enviromental Health Perspectives, 125(9).<br />
Green, R., Lanphear, B., Hornung, R., Flora, D., Martinez-Mier, E. A., Neufeld, R., Ayotte, P., Muckle, G., & Till, C. (2019). Association Between Maternal Fluoride Exposure During Pregnancy and IQ Scores in Offspring in Canada. JAMA Pediatrics, 1–9.<br />
Huber, R. S., Kim, T.-S., Kim, N., Kuykendall, M. D., Sherwood, S. N., Renshaw, P. F., & Kondo, D. G. (2015). Association Between Altitude and Regional Variation of ADHD in Youth. Journal of Attention Disorders.<br />
Malin, A. J., & Till, C. (2015). Exposure to fluoridated water and attention deficit hyperactivity disorder prevalence among children and adolescents in the United States: an ecological association. Environmental Health, 14(1), 17.<br />
Perrott, K. W. (2018). Fluoridation and attention deficit hyperactivity disorder a critique of Malin and Till (2015). British Dental Journal, 223(11), 819–822.<br />
Perrott, K. W. (2020). Health effects of fluoridation on IQ are unproven. New Zealand Medical Journal, 133(1522), 177–179.<br />
Santa-Marina, L., Jimenez-Zabala, A., Molinuevo, A., Lopez-Espinosa, M., Villanueva, C., Riano, I., Ballester, F., Sunyer, J., Tardon, A., & Ibarluzea, J. (2019). Fluorinated water consumption in pregnancy and neuropsychological development of children at 14 months and 4 years of age. Environmental Epidemiology, 3. <br />
Thomas, D. B. (2014). Fluoride exposure during pregnancy and its effects on childhood neurobehavior: a study among mother-child pairs from Mexico City, Mexico [University of Michigan].<br />
Thomas, D., Sanchez, B., Peterson, K., Basu, N., Angeles Martinez-Mier, E., Mercado-Garcia, A., Hernandez-Avila, M., Till, C., Bashash, M., Hu, H., & Tellez-Rojo, M. M. (2018). OP V – 2 Prenatal fluoride exposure and neurobehavior among children 1–3 years of age in mexico. Environmental Contaminants and Children’s Health, 75(Suppl 1), A10.1-A10.<br />
Till, C., Green, R., Flora, D., Hornung, R., Martinez-mier, E. A., Blazer, M., Farmus, L., Ayotte, P., Muckle, G., & Lanphear, B. (2020). Fluoride exposure from infant formula and child IQ in a Canadian birth cohort. Environment International, 134(September 2019), 105315.