Irish study of 2,495 older adults finds no link between lifetime fluoridated water and cognition
In an analysis of Irish Longitudinal Study on Ageing data, cumulative exposure to fluoridated tap water showed no association with MMSE or MoCA errors after adjustment.
Researchers at Trinity College Dublin report in the Journal of Dental Research that lifetime exposure to community water fluoridation (CWF) was not associated with cognitive function in older Irish adults. sagepub.com
Journal of Dental Researchsagepub.comOpen source ↗ They analyzed wave 3 (2014 to 2015) of the Irish Longitudinal Study on Ageing (TILDA), which included 6,684 participants. Fluoride exposure estimates were available for 2,495 of them, with a mean age of 65.32 years (standard deviation 8.64). Ireland introduced nationwide water fluoridation in 1964.
How exposure and cognition were measured
Lifetime exposure (at least 50 years) and early-life exposure (ages 0 to 5 years) were estimated by linking each participant's residential history to national water fluoride monitoring data. The primary exposures were cumulative lifetime exposure to fluoridated water (continuous) and percentage lifetime exposure, classified as low (below 25%), medium (25% to 75%) or high (above 75%).
Cognition was assessed with the Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA). The outcome was the error score, 30 minus the raw score, so higher values mean poorer cognition. The authors used multivariable negative binomial regression adjusted for sociodemographic, lifestyle, health, loneliness and health care access factors.
Results and limits
Cumulative exposure showed no association with errors: the incidence rate ratio (IRR) was 1.00 for MMSE (95% CI 0.99 to 1.01) and 1.00 for MoCA (95% CI 1.00 to 1.01). sagepub.com
Journal of Dental Researchsagepub.comOpen source ↗ In unadjusted models, the high-exposure group had fewer errors than the low-exposure group (IRR 0.62 for MMSE, 0.72 for MoCA). In fully adjusted models the difference was not significant (IRR 1.17 for MMSE, 95% CI 0.88 to 1.56; 1.10 for MoCA, 95% CI 0.94 to 1.29).
Early-life exposure did not modify these associations for either test (p interaction above 0.05). Only 5% of the sample, 124 people, had early-life exposure, which the authors note limits conclusions on that aspect. The absence of an association does not prove that fluoride is harmless to the brain; it means no evidence of harm was found in this cohort.
Lead author Vinay Sharma said the findings provide reassurance that lifetime exposure to fluoridated drinking water at the levels used in Ireland is not associated with poorer cognitive function in older adults.
