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Does fluoride exposure lower cognitive function in children?

May 1, 2018
What can clinicians and patients make of a 2017 study that found a correlation between in-utero fluoride exposure and lowered IQ? Let's take it from the top.

By now, many of you have heard of the research done by Bashash et al. that examined the effect of prenatal exposure to fluoride on cognitive function. The study was published in the September 2017 issue of Environmental Health Perspectives,1 and then, as most of these intriguing articles tend to do, it made the news. But there was a bit of confusion amid those practitioners and patients who were trying to make sense out of what was reported and understand the implications. Let’s take it from the top.

Investigators from Canada, Michigan, Indiana, Boston, New York, and Mexico partnered to learn more about the effects of higher concentrations of fluoride on the intelligence of children. Previous human and animal studies they had investigated suggested that fluoride could be neurotoxic. However, no longitudinal studies had been performed on mothers and children demonstrating that cognitive performance would be affected.

The Bashash study examined urine samples of pregnant women from low-to-moderate income areas that were taken from three hospitals in Mexico City. The women were divided into three groups: (1) those previously exposed to lead and mercury, (2) those who had calcium supplementation, and (3) those who denied a history of high-risk pregnancies and other significant health concerns. The mother-child pairs were exposed to fluoride in levels varying from 0.15 to 1.38 mg/L.

We can dismiss any sensational claims we may see in the news media regarding the study and know not to take anything out of context.

During pregnancy, samples were taken during each trimester, depending on which cohort the study subjects were placed in, and neurocognitive outcomes were measured for mothers and then children at age four, and then again for children six to 12 years old using standardized tests. In addition, the quality of the children’s individual home environments was measured. In general, findings showed that an increase in maternal urine fluoride levels was associated with lower scores on children’s cognitive function tests at age four and ages six through 12 years.

As with most research studies, limitations must be noted. The authors of this study were forthcoming with issues that could have impacted the findings. Here are some examples:

Fluoride was measured in spot urine samples rather than 24-hour urine collections.

Some cohorts had higher average bone lead and blood mercury levels, raising the issue of potential bias.

There were some missing data pertaining to covariate and sensitivity variables.

There was a lack of information about iodine in salt, which might modify associations between fluoride and cognition.

Results could not be referenced to the general population given the lack of data on fluoride pharmacokinetics during pregnancy.

In addition to these issues—which are concerning—there was another limitation not mentioned in this paper for which notice should be taken. The sample for this study represented mothers and children from low- and moderate-income groups. No control was made for the quality and effectiveness of the education of the children. No evaluation was made for language development based on family verbalizations, which impacts the child’s ability to communicate and read, and also relates to vocabulary development. These variables would affect cognitive function and scores on standardized tests, likely far more than fluoride exposure. A discussion of how these measures were addressed, controlled, or evaluated never occurred. A learning specialist and elementary educator might look at this paper and see a very different picture than someone assessing fluoride levels and cognitive function.

The authors of this study clearly state that additional research is needed. Thus, we can dismiss any sensational claims we may see in the news media regarding the study and know not to take anything out of context. There is no need to discontinue in-office or at-home fluoride therapy, and we can reassure patients that our experience in the United States is different from that which occurred in Mexico City. The US Environmental Protection Agency restricts the amount of fluoride in public drinking water to protect us from fluoride contamination, fluorosis, bone fractures, and neurotoxicity. Further, and equally important, we should remain discerning of current science and encourage continued quality research on this important topic.


1. Bashash M, Thomas D, Hu H, et al. Prenatal fluoride exposure and cognitive outcomes in children at 4 and 6–12 years of age in Mexico. Environ Health Perspect. 2017;125(9):097017. doi: 10.1289/EHP655.

JOANN R. GURENLIAN, RDH, PhD, is president of Gurenlian & Associates, and provides consulting services and continuing education programs to health-care providers. She is a professor and dental hygiene graduate program director at Idaho State University, and past president of the International Federation of Dental Hygienists.