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Validity of spot urine samples for estimating systemic fluoride exposure in children across diverse fluoridation modalities

Lookup NU author(s): Emerita Professor Anne Maguire, Dr Roy SandersonORCiD

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).

Abstract

© 2026 The Authors. Published by Elsevier GmbH. This is an open access article under the CC BY license. http://creativecommons.org/licenses/by/4.0/AbstractObjectiveReliable biomarkers are essential for assessing children's fluoride exposure, yet 24-h urinary fluoride excretion (24 h-UFE), the gold standard, is logistically challenging to collect. The validity of spot urine samples as a proxy across fluoridation modalities has not been evaluated. This study is the first to assess the predictive accuracy of spot urine fluoride concentration (UFC), creatinine-adjusted (UF/CR), and specific gravity-adjusted (UF/SG) for estimating 24 h-UFE across multiple fluoride exposure modalities.MethodsIn this multi-modality observational study, 178 children aged 4–6 years residing in regions with different fluoride modalities were included: water fluoridation (UK, Brazil), salt fluoridation (Colombia), milk fluoridation (Chile), and non-fluoridated areas (UK, Chile). Each child provided one 24-h urine sample and four spot samples during a separate session (post-breakfast, post-lunch, before bedtime, first morning void). Linear regression models assessed the predictive validity of UFC, UF/CR, and UF/SG.ResultsMean urinary fluoride ranged 0.48–1.38 mg/L (UFC), 1.13–2.30 mg/g (UF/CR), and 0.55–1.70 mg/L (UF/SG). UFC showed the strongest association with 24 h-UFE (mean R2 = 77%), particularly in water-fluoridated areas (up to 85%). UF/CR and UF/SG correlations were weaker (mean R2 = 58% and 61%). Accuracy improved when multiple spot samples were used. Timing of peak fluoride excretion varied: post-breakfast (water), post-lunch (salt), first morning void (milk and non-fluoridated areas).ConclusionSpot UFC provides a practical alternative for population-level monitoring of fluoride exposure in children, although accuracy depends on sampling time and fluoridation modality. This multi-modality study demonstrates variability in fluoride excretion across sources and informs optimized sampling strategies for public health surveillance.

Publication metadata

Author(s): Zohoori FV, Buzalaf MAR, Maguire A, Sanderson R, Giacaman RA, Martignon S, Beltran EO, Vasquez Y, Eskandari F, Kronic J, Gambetta-Tessini K, Levy FM

Publication type: Article

Publication status: Published

Journal: International Journal of Hygiene and Environmental Health

Year: 2026

Volume: 274

Print publication date: 01/05/2026

Online publication date: 06/04/2026

Acceptance date: 31/03/2026

Date deposited: 13/04/2026

ISSN (print): 1438-4639

ISSN (electronic): 1618-131X

Publisher: Elsevier GmbH

URL: https://doi.org/10.1016/j.ijheh.2026.114795

DOI: 10.1016/j.ijheh.2026.114795

Data Access Statement: The data that support the findings of this study are available from the corresponding author upon reasonable request

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