Fluoride Exposure and ADHD: A Systematic Review of Epidemiological Studies

Published In: Medicina
Publication Year: 2023

Study Design

This article is a systematic review of observational studies examining the link between fluoride exposure and ADHD in children and adolescents.

Funding Sources

The study was funded by:

• “Dipartimenti di Eccellenza 2018–2022” to UNIMORE Department of Biomedical, Metabolic and Neural Sciences

• “UNIMORE FAR 2021 and 2022, FOMO Line” by the University of Modena and Reggio Emilia and Fondazione di Modena

PICO Framework - what was studied and how?

Population:
Healthy children and adolescents

Intervention (Exposure):
Fluoride exposure from any source (e.g., water, food, urinary biomarkers)

Comparison:
Populations with low or no fluoride exposure

Outcomes:
Development or symptoms of ADHD

In Paragraph Form:
This systematic review evaluated epidemiological evidence on whether fluoride exposure in children and adolescents is associated with an increased risk of ADHD. The review compared populations with varying levels of fluoride exposure, measured through water fluoride content or urinary fluoride levels, against those with lower or no exposure. ADHD outcomes were assessed through validated questionnaires, parental reports, or clinical diagnoses.

Inclusion and Exclusion Criteria

Inclusion Criteria:

• Studies involving children or adolescents

• Exposure to fluoride via any route

• Reported ADHD-related outcomes

• Observational study designs (ecological, cross-sectional, case-control, or cohort)

Exclusion Criteria:

• Reviews, editorials, or studies not addressing ADHD as an outcome

Demographics and Study Design

• Total studies included: 7 distinct studies (8 papers)

• Designs: 5 cross-sectional, 1 cohort, 1 case-control

• Geographic spread: USA, Canada, Mexico, China, India

Sample Sizes:

• Ranged from 150 (smallest) to over 76,000 (largest)

• Some studies used national health surveys, others used clinical cohorts

Primary Outcome Variables and Results

Main Outcome:
Association between fluoride exposure and ADHD diagnosis or related symptoms.

Key Findings:

• 3 studies found a positive association between fluoride exposure and ADHD risk.

• 2 studies found an association between fluoride and internalizing symptoms (e.g., somatization), but not ADHD.

• 3 studies found no association between fluoride exposure and ADHD.

Example Results:

• A 1 mg/L increase in tap water fluoride was associated with a 6.1-fold increase in ADHD diagnosis odds in Canadian youth (Riddell et al., 2019).

• In Mexico, higher prenatal fluoride exposure was linked to inattention but not hyperactivity (Bashash et al., 2018).

• Other studies (e.g., Barberio et al., 2017) found no statistically significant correlation.

Statistical Reporting:

• Specific p-values and confidence intervals varied by study and were not always uniformly reported due to heterogeneity.

Conclusions

The review suggests potential neurotoxic effects of fluoride on neurodevelopment, especially related to cognitive and psychosomatic symptoms linked with ADHD. However, due to significant heterogeneity in study designs, exposure measurements, and outcome assessments, the evidence is not strong enough to confirm a causal relationship between fluoride exposure and ADHD.

Discussion: Strengths and Limitations

Strengths:

• Comprehensive search and systematic methodology (PRISMA-compliant, PROSPERO-registered)

• Inclusion of multiple types of fluoride exposure assessments

• Geographic diversity of the studies

Limitations:

• Heterogeneity in diagnostic criteria and fluoride measurement methods

• Many studies did not use validated ADHD diagnostic tools

• Potential confounding from unmeasured environmental or social factors

• Limited number of high-quality longitudinal studies

Citation

Fiore G, et al. Fluoride Exposure and ADHD: A Systematic Review of Epidemiological Studies. Medicina. 2023;59(4):797. 

Link to study.

Visual Aids

Simple Chart: Association of Fluoride with ADHD