Background
Concerns about fluoride’s potential neurotoxic effects persist, though most available evidence originates from
regions with high fluoride concentrations in drinking water (1.5–20+ ppm), limiting applicability to Ireland’s 0.7 ppm
levels. The Health Research Board review (2022) identified insufficient evidence on developmental implications.
While no clear harm has been established, the review called for methodologically rigorous longitudinal studies to
address existing gaps and assess risks. To address this, present study aims to investigate these suggested effects
in relation to Ireland’s mandatory community water fluoridation (CWF) policy that has been in place since 1964.
Objectives
(1) To investigate potential neurodevelopmental and cognitive effects of CWF in Irish children and cognitive
function in adults, and
(2) To assess CWF’s oral health benefits in the current Irish context, where multiple fluoride sources and improved
dental hygiene practices have evolved since 1964.
Methods
We will analyse two nationally representative cohorts linked to comprehensive national fluoridation data:
Growing Up in Ireland (GUI) – Tracking 20,000 children recruited when they were 9 months or 9 years old, with
validated neurodevelopmental, cognitive, behavioural, and educational attainment assessments, oral health
outcomes and extensive confounding variables collected across five/six waves.
The Irish Longitudinal Study on Ageing (TILDA) – Following 8,000 older adults across multiple waves, with
cognitive function and oral health assessments, including systemic health markers (biological/neuroimaging).
Individual-level fluoride exposure will be calculated using geocoded residential histories and water supply
fluoridation records. Advanced multilevel models will account for clustering, temporal trends, and key confounders
including socioeconomic status, diet, and dental hygiene practices.
This study will provide the first comprehensive evidence on CWF effects at regulated levels using individual
longitudinal exposure data and validated outcomes. Findings will directly inform Irish water management and oral
health policies, while contributing considerable evidence internationally, relevant for regions implementing or
considering water fluoridation programs.
