Lifetime Fluoride Exposure and Cognition in Older Irish Adults

Community water fluoridation (CWF) is an effective public health intervention to prevent dental caries. This study investigated potential associations between lifetime fluoride exposure from CWF and cognitive outcomes in older Irish adults and whether early-life exposure modified these associations. Data from the Irish Longitudinal Study on Ageing (TILDA; wave 3, 2014 to 2015) were analyzed (n = 6,684). Lifetime (≥50 y) and early-life (ages 0 to 5 y) fluoride exposures were estimated by linking residential histories to national water fluoride monitoring data and were available for N = 2,495 participants (mean age 65.32 y, standard deviation 8.64 y). Primary exposures were cumulative lifetime exposure to fluoridated water (CLEFW; continuous) and percentage lifetime exposure to fluoridated water (%LEFW), classified as low (<25%), medium (25% to 75%), or high (>75%). Cognitive outcomes were Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA) error scores (30 minus raw scores), with higher scores indicating poorer cognition. Associations were examined using multivariable negative binomial regression models, adjusted for sociodemographic, lifestyle, health, loneliness, and health care access factors. Effect modification by early-life fluoride exposure (any/none) was tested using interaction terms. CLEFW showed no association with cognitive errors (incidence rate ratio [IRR]_MMSE = 1.00, 95% confidence interval [CI]: 0.99 to 1.01; IRR_MoCA = 1.00, 95% CI: 1.00 to 1.01). In unadjusted models, the high-exposure %LEFW group had lower cognition errors than the low-exposure reference group (IRR_MMSE = 0.62, 95% CI: 0.49 to 0.79; IRR_MoCA = 0.72, 95% CI: 0.62 to 0.83), but these became nonsignificant in fully adjusted models (IRR_MMSE = 1.17, 95% CI: 0.88 to 1.56; IRR_MoCA = 1.10, 95% CI: 0.94 to 1.29). There was no evidence of effect modification by early-life fluoride exposure for either cognitive outcome (p_interaction > 0.05). Lifetime fluoride exposure from CWF was not associated with later-life cognitive function in older Irish adults, and there was no statistical evidence of effect modification by early-life exposure.