Identifying Critical Periods of Neurotoxicity to Fluoride Exposure in Canadian Children
Bibliographic record
Abstract
Background: Fluoride is associated with IQ deficits during early brain development, but the period in which children are most vulnerable has not been established. We assessed sex-specific effects of fluoride on IQ across prenatal, infancy, and early childhood windows. Methods: Repeated exposures from 596 mother-child pairs in the Maternal-Infant Research on Environmental Chemicals cohort were analyzed using GEE to explore associations between fluoride exposures and IQ after adjustment for covariates and multiple comparisons. Fluoride was measured in urine spot samples collected during pregnancy trimesters and when children were between 1.9 and 4.4 years. Infant fluoride exposure was estimated from water fluoride concentration and duration of formula-feeding over the first year of life. The Wechsler Preschool and Primary Scale of Intelligence-III was administered at 3 to 4 years. Results: Among boys and girls, the association between fluoride and performance IQ (PIQ) significantly differed across exposure windows (p = .01). Among boys, prenatal exposure to fluoride was most strongly associated with adverse deficits on PIQ, B = -8.45 (95% CI: -12.90, -3.99), followed by infancy, B = -2.81 (95% CI: -6.59, 0.98), but not childhood, B = 0.20 (95% CI: -2.58, 2.99), respectively. Among girls, infancy exposure to fluoride was most strongly associated with adverse deficits on PIQ, B= -5.19 (95% CI: -8.84, -1.53), followed by prenatal and childhood exposures, B = -3.50 (95% CI: -9.51, 2.51), B = -2.05 (95% CI: -2.58, 2.99), respectively. Estimates for full-scale IQ were weaker but showed strongest effects for boys in the prenatal exposure period. Effects across all windows were nonsignificant among girls. We found no significant sex-specific associations between fluoride and verbal IQ. Conclusion: Adverse associations between fluoride exposures and cognitive outcomes may depend on timing and biological sex, with the prenatal window potentially critical for boys, while infancy is potentially critical for girls. Keywords: Fluoride, critical windows, water quality, children’s neuropsychology, epidemiology, toxicology.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.003 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.002 | 0.004 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".