Fluoride exposure during early adolescence and its association with internalizing symptoms

Early, chronic, low-level fluoride exposure has been linked to attention-deficit hyperactivity disorder (ADHD) and learning deficits in children. Rodent studies suggest a link between fluoride exposure and internalizing behaviors. No human studies have examined the impact of fluoride on internalizing behaviors during adolescence.

Evaluate the relationship between urinary fluoride and early adolescent internalizing symptoms in the Cincinnati Childhood Allergy and Air Pollution Study (CCAAPS).

Participants in CCAAPS provided non-fasting spot urine samples at age 12 years (n = 286). Urine samples were analyzed using a microdiffusion method to determine childhood urinary fluoride (CUF) concentrations and were log-transformed for analyses. Caregivers of CCAAPS participants completed the Behavior Assessment System for Children-2 (BASC-2) at the age 12 study visit to assess internalizing symptoms (e.g., anxiety, depression, somatization), and a composite score of the three domains; T-scores ≥ 60 were used to identify adolescents in a clinically "at-risk" range. Race, age of the adolescent, household income, maternal age at birth, caregiver depression, caregiver-child relationships, and age 12-year serum cotinine concentrations were considered covariates in regression models. Sex-specific effects of fluoride exposures were investigated through the inclusion of interaction terms.

Higher CUF concentrations were significantly associated with increased somatization (β = 3.64, 95% CI 0.49, 6.81) and internalizing composite T-scores in a clinically "at-risk" range (OR = 2.9, 95% CI 1.24, 6.9). Compared to females, males with higher CUF concentrations had more internalizing (p_interaction = 0.04) and somatization symptoms (p_interaction = 0.02) and were nearly seven times more likely to exhibit "at-risk" internalizing symptomology. CUF concentrations were not significantly associated with depression or anxiety symptoms.

This is the first study to link fluoride exposure and internalizing symptoms, specifically somatization. Somatization represents an interface of physical and psychological health. Continued follow-up will help shed light on the sex-specific relationship between fluoride and mental health and the role of somatization.