Appraisal Neurodevelopmental Disorders

Fluoride ADHD study has weak biased methods

Publication reviewed:

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

Malin AJ, Till C — Environmental Health

Public health dentist, Shivani Arora appraised a widely discussed fluoride ADHD paper for Fluoride Science.

Fluoride ADHD study data that suffers from weak methods and biased data


An ecological design was used to examine if states with more widespread water fluoridation would have higher ADHD prevalence. State-based ADHD prevalence estimates (2003, 2007, 2011) and fluoridation prevalence (for years 1992, 2000, 2002, 2004, 2006, and 2008) were obtained from the Centers for Disease Control and Prevention website, and then statistical analyses were performed using these estimates. The authors concluded that there is an association between ADHD prevalence and fluoridation prevalence and hence the fluoridated water may be an environmental risk factor. However, some of the findings are not consistent with their hypothesis of interest and also, the internal validity of this fluoride ADHD study is highly questionable. The authors acknowledged that there was no previous research linking fluoridation to ADHD. At best, this study can serve to generate a hypothesis. As it stands, this study is not a strong argument for concern.


  • A – Strong methodology and unbiased, appeared in peer-reviewed in respected science journal
  • B – Strong methodology and unbiased, not in peer-reviewed journal
  • C – Weak methodology and/or biased
  • F – Not a scientific finding


  • High – All the peer-reviewed research to date support these findings, and a significant amount of research has been done in this area.
  • Medium – Most, but not all, peer-reviewed research to date support these findings, and a significant amount of research has been done in this area.
  • Low – Not a lot of research has been done in this area, or some, but not most, other peer-reviewed research supports these findings.
  • Not Supported – No other studies support this study’s conclusions.
  • Contradicted – Most studies contradict this study’s conclusions.


There are no strengths.


It’s an ecological study design with 51 observations (50 states & DC), and is not appropriate to test any hypothesis about fluoride and ADHD. ADHD prevalence was based on self-reported data, and hence had a potential of misclassification of disorder status. State-wide fluoridation measures were used. Individuals’ exposure to fluoridation were not measured. Due to ecological assessment of exposure to fluoride in drinking water and the use of prevalence data of self-reported ADHD and water fluoridation from different years, the findings are at high risk for ecological fallacy. Authors did not adjust for important confounders (smoking, low birth weight, age, sex etc.). Moreover, authors’ poor literature review and skewed interpretation of literature concerning fluoride and neurodevelopmental defects may have introduced bias.


They used life-time ADHD prevalence for their study. They should also have considered using current diagnosis of ADHD as the disorder regresses with age. Authors failed to control for important confounders (blood lead levels, smoking, low birth weight, gender etc.). This makes the internal validity of this fluoride ADHD research questionable.