What the research found
The authors analyzed data from the Early Life Exposures in Mexico to Environmental Toxicants (ELEMENT) project to examine if prenatal exposure to fluoride is associated with declined childhood intelligence.
Subjects: The ELEMENT project recruited women who were 14 or less weeks pregnant and free of medical, mental disorders, high-risk pregnancy as well as use of recreational alcohol and drugs use at three clinics of the Mexican Institute of Society Security in Mexico City that serve low-to-moderate income populations.
Exposure measure: Prenatal F exposure was measured as an averaged value of maternal creatinine-adjusted urinary fluoride concentrations (maximum three and minimum one spot urine sample[s] were archived for each woman).
Outcome measure: Offspring’s neurocognitive outcomes were measured as the General Cognitive Index (GCI) score at 4 years and IQ score at 6-12 years.
Covariates: Maternal age, education, marital status, birth order, birth weight, gestational age at delivery, maternal smoking, maternal IQ (estimated using selected subtests of the WAIS-Spanish measured at 6-12 months after birth), and cohort ID. The specific-gravity adjusted urinary fluoride values obtained from offspring at 6-12 years of age were included in the model for prenatal F exposure and IQ.
The study found:
- Significant correlation between GCI and IQ scores.
- No significant correlation between prenatal creatinine-adjusted urinary fluoride and offspring’s specific-gravity adjusted urinary fluoride levels at 6-12 years of age.
- Prenatal creatinine-adjusted urinary fluoride level and GCI at 4 years of age showed mild linear relationship: 0.5mg/L increase in prenatal urinary fluoride was associated with 3.15-point drop in GCI scores (p=0.01, N=287).
- Prenatal urinary fluoride level and IQ at 6-12 years of age showed mild curvilinear relationship: 1) no clear association between prenatal urinary fluoride and IQ scores below approximately 0.8mg/L urinary fluoride levels, and 2) a negative association above prenatal urinary fluoride 0.8mg/L. The authors found 0.5 mg/L increase in prenatal urinary fluoride was associated with -2.5 points in IQ scores (p=0.01, N=211).
- Sensitivity analyses conducted for the subsets of data (N<200) indicated the following:
- The negative associations between prenatal urinary fluoride and GCI or IQ persisted with further adjustment for other potential confounders (family possession, maternal bone lead and blood mercury levels). The effect estimates were attenuated when family possession (SES proxy) and maternal blood mercury values were adjusted in the models relative to unadjusted models, while all of the effect estimates were higher in the subset of subjects with available data of SES, maternal bone lead and blood mercury levels.
- There was no clear, statistically significant, association between contemporaneous children’s urinary fluoride and IQ at 6-12 years of age either unadjusted or adjusted for maternal urinary fluoride during pregnancy.