Prenatal Fluoride Exposure and Attention Deficit Hyperactivity Disorder (ADHD) in Children

What is the headline saying?
Link to article Prenatal Fluoride Exposure Linked to ADHD in Kids

What is the article saying?

Prenatal exposure to higher levels of fluoride not only impairs cognitive development but also significantly increases the incidence of attention-deficit/hyperactivity disorder (ADHD) in children, new research shows.

…it is the first [study] to find an increased incidence of ADHD with prenatal fluoride exposure.

We observed a positive association between higher prenatal fluoride exposure and more behavioral symptoms of inattention, which provide further evidence suggesting neurotoxicity of early-life exposure to fluoride.

Does the headline ultimately support claims made by the article? Does it summarize key points of the article?
Yes. However, the lead author makes sure to say that this study does not summarize the debate about whether or not fluoride should be added to water sources. See below:

For the past 50 years, the medical establishment has claimed that fluoride is safe and effective; should the official position on fluoridation change? I do not believe our study alone can be used to answer this question.

What are the implications of the headline and article?
Countries and geographical areas that artificially add fluoride to water, have it naturally occurring in the environment, or add it to salt are putting fetuses and, consequently, kids at risk for ADHD.

They fuel the debate about whether or not fluoride should be removed from the drinking water in countries that have implemented this public health intervention.

What evidence currently exists to counter or support these implications?

Fluoridation and attention deficit hyperactivity disorder – a critique of Malin and Till (2015)

Fluoride exposure and reported learning disability diagnses among Canadian children: Implication for community water fluoridation

Exposure to fluoridated water and attention deficit hyperactivity disorder prevalence among children and adolescents in the United States: and ecological association

Are there similar and/or opposing headlines from other news outlets? Do the news outlets only link back to other news outlets?
There are similar headlines all tied to the same study – Google Search

What are the data sources (i.e. memo, official statement, official document, research study,  validated surveillance system, official report, etc.) supporting the article?
Research Study: Prenatal fluoride exposure and attention deficit hyperactivity disorder (ADHD) symptoms in children at 6-12 years of age in Mexico City.

Are these data sources credible when applied to the news story? Why or why not?
Data source is not credible due to limitations of the study. Please continue reading for more details. Also, please read the limitations section of the study:

Study participants

Three different cohorts of women in the Early Life Exposures to Environmental Toxicants (ELEMENT) birth cohort study with available maternal urinary samples during pregnancy, along with child assessments of ADHD-like behaviors at age 6-12.


Screening for ADHD

  • Mothers completed Conners’ Rating Scale-Revised (CRS-R)
  • Conners’ Continuous Performance Test (CPT II) was administered to children ages 6-12 years of age
  • Conners Scale for Assessing ADHD
    • As with all psychological evaluation tools, the Conners CBRS has its limitations. Those who use the scale as a diagnostic tool for ADHD run the risk of incorrectly diagnosing the disorder or failing to diagnose the disorder. Experts recommend using the Conners CBRS with other diagnostic measures, such as ADHD symptom checklists and attention-span tests.

To measure fluoride levels in urine:

The 24-hour urine collection should be used wherever possible…but 14–16 or even 8-hour collection can be used if necessary. Where 24-hour or continuous supervised collection periods are not possible, spot samples of urine can sometimes provide valuable information…

A spot urine sample is defined as an un-timed “single-void” urine sample. This method is the least informative method for studying fluoride exposure, because the amount of fluoride excreted per day or per hour cannot be calculated from the concentration alone.

If spot samples are collected, it is best to take them at several times within a day. Urine that has accumulated in the bladder over a short period may reflect a short-lived peak level of the fluoride concentration. Hence, the longer the urine is retained in the bladder, the more representative it is of 24-hour results. For each spot sample, the hour when it was obtained should be recorded. When spot samples are collected in a follow-up assessment of urinary fluoride, the time of day at which the urine is passed should be approximately equal to the collection times in the initial excretion study. In programmes where fluoride is given once or twice per day, spot urine samples are not useful unless they are scheduled in such a way as to be directly associated with the fluoride intake. 

Attention outcomes of interest:

  • Diagnostic and Statistical Manual of Mental Disorders – 4th edition (DSM-IV) criteria for ADHD, Conners’ ADHD Indices (CRS-R), Conners’ Continuous Performance Test (CPT-II)
    • DSM-IV Inattention Index
    • DSM-IV Hyperactive-Impulsive Index
    • DSM-IV Total Index (Inattentive, Hyperactive-Impulsive)
    • Cognitive Problem/Inattention and Hyperactivity Index
    • Conners’ ADHD Index and CGI: Restless-Impulsive


Selected apriori – based on theoretical relevance or observed associations with fluoride exposure and/or the analyzed neurobehavioral outcomes

Used questionnaire at first pregnancy visit to collect information on maternal factors. Used questionnaire to collect demographics on infant at pregnancy. Mothers took socioeconomic status questionnaire during visit where psychometric tests were conducted. The Home Observation for Measurement of the Environment (HOME) Inventory was given to a subset of participants at the same time as the neurobehavioral tests.

Data analysis

After univariate and bivariate analysis:

  • Initial fully adjusted linear regression
    • Outcomes = skewed residuals
  • Corrected with Gamma regression with identity link GLM with a Gamma-distributed Dependent Variable
    • Used to examine the adjusted association between prenatal fluoride and each neurobehavioral outcome
  • Model adjustments
    • Model adjusted based on maternal factors, adjusted based on infant-specific factors and socioeconomic status, and adjusted for potential cohort and Ca+ intervention effects
    • Potential confounders – sensitivity analyses involving subset
      • HOME Inventory
      • Child contemporaneous fluoride exposure measured by child urinary fluoride adjusted for specific gravity
      • Maternal blood mercury
      • Maternal bone lead
  • Cook’s D
  • Generalized Additive Models (estimated using cross validation in R)
    • Visualize adjusted association between fluoride exposure and measures of attention to examine non-linearity (tested using the inclusion of a quadratic term in the model)
  • Applied Benjamin-Hochberg false discovery rate procedure to address multiple testing corrections (Q = .5, m = 10 tests)


Only 10% of mother-child pairs fell within clinically significant range for CRS-R and MUFcr (average of all urinary samples)

  • Inattention was based on CRS-R; not hyperactivity or CPT-II outcomes (CPT-II fell within average range)
  • Higher concentration of MUFcr associated with parent-endorsed symptoms (statistically significant even after multiple corrections)
    • DSM-IV Inattention
    • DSM-IV Total ADHD
    • Cognitive Problem/Inattention Index
    • ADHD Index


Sensitivity analyses did not change CRS-R scores

Observations of MUFcr and CRS-R suggest that higher levels of urinary fluoride concentration did not increase ADHD-like symptoms


From article:

  • Cohort study not initially designed to look at fluoride exposure
  • Did not take routine samples for the majority of participants for each trimester
  • Cannot relate how intake of fluoride relates to concentration in pregnant women
  • No family history or genetic markers collected
  • No clinical diagnosis of ADHD
  • No teacher reports of ADHD using CRS-R
  • No functional consequences of symptoms characterized to clinically diagnosis the disorder

My additions:

  • Convenience sample
  • Focused on women in Mexico who consume water that naturally has fluoride (it is not artificially added) as well as salt that also has fluoride; not broadly generalizable
  • Limited opportunity for public health intervention regarding the source of naturally-occurring fluoride in water
  • Spot samples not adequate to make strong conclusions, need to record the time samples were taken (and also take multiple samples)


From authors of the study:

In summary, we observed a positive association between higher prenatal fluoride exposure and more behavioral symptoms of inattention, but not hyperactivity or impulse control, in a larger Mexican cohort of children aged 6 to 2 years. The current findings provide further evidence suggesting neurotoxicity of early-life exposure to fluoride. Replication of these findings is warranted in other population-based studies employing biomarkers of prenatal and postnatal exposure to fluoride.


What does this mean for the general public?

The headline and news article mirror the conclusions made by the authors, however, the claims by the authors that their findings provide evidence that suggests neurotoxicity of early-life exposure to fluoride are not valid based on the limitations of this study (many of which the authors point out themselves).


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Scrutinizer Analysis_actionable summary1_Fluoride


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