Urinary Fluoride Levels Among Canadians and the Association Between Fluoride Exposure and Attention Deficit Hyperactivity Disorder

Fluoride has been identified as a developmental neurotoxin a claim that is uncontested at high exposure levels, but remains debated at low exposure levels. In Canada, 39% of municipalities add fluoride to their drinking water at a recommended level of 0.7ppm. Exposure to fluoride has been linked with increased prevalence of attention deficit hyperactivity disorder (ADHD) in the United States and symptoms of inattention in Mexican children. This dissertation consists of one study examining the association between fluoride exposure and symptoms of ADHD in youth, and a second study examining the predictors of an individuals level of urinary fluoride. Study 1 used cross-sectional data on youth 6 to 17 years of age from the Canadian Health Measures Survey (CHMS, Cycles 2 and 3). Urinary fluoride concentrations were measured in spot samples and adjusted for specific gravity (UFSG, n=1877) and water fluoride concentrations were measured in tap water samples (n=980). We used logistic regression to test the association between fluoride exposure and ADHD diagnosis and linear regression to examine the relationship between fluoride exposure and the hyperactive-inattention subscale score on the Strengths and Difficulties Questionnaire (SDQ). UFSG did not predict ADHD diagnosis or SDQ score, whereas a 1 mg/L increase in tap water fluoride level was associated with 6.1 times higher odds of an ADHD diagnosis (95% CI = 1.60, 22.8) and a 1.5 increase in SDQ score for adolescents. Study 2 used data from Cycle 3 of the CHMS to examine factors that influence urinary fluoride levels in a sample of 1629 individuals aged 3 to 79 years. In the linear regression models, tap water fluoride level, community water fluoridation status, age, sex, BMI, smoking allowed in the home, and tea consumption were significant predictors of UFSG. Community water fluoridation and tap water fluoride were associated with higher levels of fluoride excretion and with an increased risk of ADHD symptoms and diagnosis among Canadian youth. These findings highlight the need to identify subgroups who may have especially high levels of exposure and to further investigate the potential for fluoride-mediated developmental neurotoxicity in populations with community water fluoridation.