Fluoride Exposure Among U.S. Children Aged ≤ 19 Years: Findings from NHANES 2013–2016

Abstract

Community water fluoridation is a key public health intervention, yet ongoing debates about systemic risks call for evidence on fluoride exposure. We analyzed NHANES 2013–2016 biomonitoring data to assess fluoride exposure in children and adolescents aged 0–19 years. We calculated the proportion of children with fluoride levels in relation to guidelines from the United States Environmental Protection Agency (USEPA), World Health Organization (WHO), and Centers for Disease Control and Prevention (CDC). Biomonitoring data was obtained from the National Health and Nutrition Examination Survey (NHANES). Median water fluoride concentration was 0.50 (95% CI: 0.35, 0.64) mg/L for males, 0.49 (95% CI: 0.35, 0.63) mg/L for girls, 0.49 (95% CI: 0.35, 0.63) for the <3 age group, and 0.50 (95% CI: 0.36, 0.64) for the 18–19 age group. Median urine fluoride concentration was 0.56 (95% CI: 0.51, 0.62) mg/L for males, 0.46 (95% CI: 0.41, 0.50) for girls, 0.59 (95% CI: 0.50, 0.62) for the age group 6–8, and 0.51 (95% CI: 0.42, 0.60) for the 18–19 age group. Of the children, 99.96% were below the EPA’s enforceable 4.0 mg/L limit, 99.05% below the EPA’s 2.0 mg/L limit, and 98.6% below the WHO 1.5 mg/L standard. For urinary fluoride, 88.1% were within the CDC reference range of 0.2–<3.2 mg/L. We found that water fluoride levels did not vary across age and sex groups, but urine fluoride levels changed. Results indicate that most children remain within regulatory agencies’ guidelines.

1. Introduction

Community water fluoridation has been a cornerstone of dental public health policy in the United States since 1945 [1]. Water fluoridation is an effective public health intervention in reducing dental caries. However, recent reevaluation of fluoridation programs in the public supply water by counties and municipalities reflects growing concerns over their safety [2]. These concerns highlight the need for updated scientific evidence on fluoride exposure levels and their health implications, particularly in children [3,4].

Fluoride is a naturally occurring groundwater chemical [5]. Fluoride concentrations vary widely across aquatic environments. Typical freshwater bodies contain <0.5 mg/L, while groundwater may contain <0.1 mg/L to >10 mg/L in regions with geologic fluoride deposits. Surface waters generally have lower concentrations than groundwater due to dilution, whereas coastal and estuarine waters average around 1.2–1.5 mg/L due to natural mineral dissolution [1,6]. In regions with elevated natural fluoride, additional fluoridation can lead to harmful exposure [6]. In areas with low groundwater fluoride, the absence of fluoridation may leave populations under-protected against dental caries [7]. In addition, we have a limited understanding of how fluoride exposure manifests at the individual level and how it varies by sociodemographic characteristics [8]. There is a notable lack of studies that concurrently assess fluoride levels in drinking water, plasma, and urine [9]. Moreover, very few investigations have evaluated fluoride exposure among U.S. children and adolescents in relation to established guidelines and recommendations from the United States Environmental Protection Agency (USEPA), WHO, Centers for Disease Control and Prevention (CDC), and clinical practice [10]. Most U.S. public water systems use standardized artificial fluoridation compounds such as fluorosilicic acid (H₂SiF₆), sodium fluorosilicate (Na₂SiF₆), or sodium fluoride (NaF) [11]. These compounds are added to achieve a target fluoride concentration of approximately 0.7 mg/L, which is the CDC-recommended optimal level for dental caries prevention [12].

We aimed to understand fluoride exposure among US children and factors associated with fluoride exposure. The objective of this study is to assess naturally occurring fluoride levels in groundwater across U.S. counties and to examine the status of public water fluoridation in these counties to understand how it aligns with natural fluoride levels. We analyzed the distribution of fluoride in household tap water, plasma, and urine across age, sex, and race among children aged 0 to 19 years. We determined the proportion of children whose fluoride exposure falls within established benchmarks: the USEPA’s non-enforceable (≤2 mg/L) and enforceable (≤4 mg/L) drinking water standards, Mayo Clinic’s plasma reference level of <1 μmol/L (Laboratories 2025), and the CDC’s urinary fluoride reference ranges, which categorize concentrations as normal (≤1.5 mg/L) and elevated (>1.5 mg/L) [12,13,14]. Despite decades of water fluoridation policy in the United States, there is limited contemporary evidence assessing fluoride exposure using multiple biomarkers (tap water, urine, plasma) within the same nationally representative cohort [15]. Previous studies have typically examined single biomarkers or focused on adults [16,17,18,19,20]. The novelty of this study lies in its multi-matrix approach, integration of geospatial groundwater data, and evaluation of fluoride exposure specifically in children. Children and the younger population overall are more susceptible due to greater intake relative to body weight and developing renal systems [21]. This study aims to provide an updated, quantitative evidence needed to support the need for reevaluation of fluoride policies.

2. Methods

2.1. Data Source

Groundwater fluoride data were obtained from the U.S. Geological Survey. County-wide water fluoridation data was retrieved from the Centers for Disease Control and Prevention [12]. Fluoride exposure data in tap water, blood and urine, as well as participant-level characteristics, were derived from the NHANES 2013–2016 among U.S. children aged 0–19 years [22]. NHANES has not released fluoride biomonitoring data for children in cycles beyond 2015–2016. Among these biomarkers, urinary fluoride was available for all participants aged 6–19 years in 2015–2016 cycles, plasma fluoride was measured only in children aged 6–19 years, and tap water fluoride was available for participants aged 0–19 years who reported household water sources were available in both 2013–14 and 2015–16 cycles. Plasma and urine fluoride were measured by the NHANES laboratory using ion-selective electrode potentiometry after microdiffusion, following CDC standard operating procedures. Household tap water fluoride was analyzed using an ion chromatography system with conductivity detection. All laboratory analyses underwent internal QC and external proficiency testing [22].

2.2. Statistical Analysis

To assess spatial patterns of naturally occurring fluoride in groundwater across the United States, we developed a county-wide choropleth map using groundwater fluoride data, depicting county-level variations in natural fluoride concentrations [23]. Counties were classified into four categories of mean water fluoride concentration: <0.2 mg/L, 0.2–<0.7 mg/L, 0.7–1.5 mg/L and >1.5 mg/L. We developed a county-level choropleth map using ArcGIS Pro 3.2. Groundwater fluoride concentrations were spatially joined to county boundaries using Federal Information Processing Series (FIPS) codes. Data were categorized into four concentration intervals (<0.2 mg/L, 0.2–<0.7 mg/L, 0.7–1.5 mg/L, >1.5 mg/L) and symbolized using a sequential color gradient. Public water fluoridation data from the CDC were overlaid as a second layer to visualize alignment between natural fluoride levels and fluoridation policy [12,24].

To evaluate the alignment of fluoridation policy with naturally occurring fluoride levels, we integrated county-level fluoridation data from the CDC on public water system fluoridation status [24]. Using GIS-based mapping, we overlaid these data sources with our choropleth map to identify how groundwater fluoride concentrations align with current water fluoridation practices [24]. We calculated the 10th, 25th, 50th, 75th, and 90th percentiles of water, plasma, and urine fluoride concentrations across age, sex, and race categories. We categorized water fluoride according to national and international guidelines: <1.5 mg/L and ≥1.5 mg/L (WHO guideline); ≤2.0 mg/L and >2.0 mg/L (EPA’s secondary non-enforceable standard); and ≤4.0 mg/L and >4.0 mg/L (EPA’s enforceable maximum contaminant level) [24]. Plasma fluoride was categorized as <1.0 µmol/L and 1.0–4.0 µmol/L, based on Mayo Clinic reference values [13]. Urinary fluoride was categorized as <0.2 mg/L, 0.2–<3.2 mg/L, and ≥3.2 mg/L based on the CDC reference range [12]. NHANES urinary fluoride concentrations are derived from spot urine samples [22]. No adjustments for urinary specific gravity or creatinine were made, consistent with NHANES laboratory reporting procedures for fluoride. We then examined the fluoride exposure categories in relation to participants’ characteristics, including race/ethnicity, sex, household poverty–income ratio, time living in the U.S., disability status, food insecurity, maternal age at childbirth, maternal smoking during pregnancy, and SNAP participation. Proportions of fluoride categories across participants’ characteristics were assessed using survey-weighted Rao–Scott Chi-square tests. Analyses incorporated NHANES sample weights, strata, and clustering variables to produce nationally representative estimates [22].

All analyses were performed using SAS software, version 9.4 (SAS Institute Inc., Cary, NC, USA). The NHANES-provided survey weights, strata, and primary sampling units were applied to account for the complex, multistage probability sampling design and to generate nationally representative estimates. Descriptive statistics were used to summarize biomarker distributions across subgroups, and the Rao–Scott chi-square test was applied to examine differences in categorical exposure groups. A two-sided p-value of <0.05 was considered statistically significant for all comparisons.

3. Results

Figure 1 suggests that most counties in the US have fluoride concentrations between 0.2 and 0.7 mg/L. Large regions in the Northeast, Midwest, and Southeast exhibited levels below 0.2 mg/L. Elevated concentrations exceeding 1.5 mg/L were observed in counties across the Southwest, including areas of West Texas and Idaho (Figure 1).

Public water fluoridation was prevalent across much of the eastern and southeastern United States, as well as portions of the Midwest and South (Figure 2). In contrast, fluoridation coverage was limited in many western counties, particularly in California, Nevada, Utah, Idaho, Montana, and parts of Texas and Oklahoma, where many systems did not fluoridate public water [25].

When both maps were overlaid, we found that counties with naturally low groundwater fluoride concentrations (<0.2 mg/L) were more likely to implement community water fluoridation programs, particularly across the Southeast and Midwest. In regions where groundwater fluoride levels were elevated (>1.5 mg/L), such as West Texas, parts of Arizona, and Idaho, public water systems were less frequently fluoridated. Several western counties demonstrated both low groundwater fluoride levels and limited fluoridation coverage [23,25].

The median water fluoride levels were consistent: 0.47 mg/L (95% CI: 0.31–0.64) for children under 3 years, 0.50 mg/L (95% CI: 0.36–0.64) for those aged 3–5 years, 0.51 mg/L (95% CI: 0.37–0.65) for those aged 6–8 years, 0.50 mg/L (95% CI: 0.36–0.63) for those aged 9–11 years, 0.50 mg/L (95% CI: 0.33–0.67) for those aged 12–14 years, 0.47 mg/L (95% CI: 0.31–0.63) for those aged 15–17 years, and 0.50 mg/L (95% CI: 0.36–0.64) for those aged 18–19 years. (

Table 1. Weighted quantiles (95% CIs) of water fluoride concentrations (mg/L) in the NHANES (2013–2014 & 2015–2026) study population in persons ≤ 19 years of age.

	Age	N	10th Percentile	25th Percentile	50th Percentile	75th Percentile	90th Percentile	Mean
All participants	All	8087	0.07 (0.04, 0.10)	0.18 (0.12, 0.23)	0.49 (0.35, 0.63)	0.72 (0.72, 0.76)	0.86 (0.75, 0.97)	0.50 (0.43, 0.57)
	<3	1783	0.07 (0.05, 0.09)	0.16 (0.11, 0.21)	0.47 (0.31, 0.64)	0.71 (0.67, 0.75)	0.85 (0.75, 0.95)	0.49 (0.42, 0.56)
	3–5	1187	0.07 (0.04, 0.10)	0.18 (0.11, 0.25)	0.50 (0.36, 0.64)	0.71 (0.67, 0.76)	0.86 (0.72, 0.99)	0.50 (0.43, 0.59)
	6–8	1311	0.07 (0.04, 0.10)	0.19 (0.13, 0.25)	0.51 (0.37, 0.65)	0.72 (0.67, 0.77)	0.89 (0.73, 1.04)	0.51 (0.43, 0.58)
	9–11	1223	0.07 (0.04, 0.10)	0.20 (0.13, 0.26)	0.50 (0.36, 0.63)	0.72 (0.66, 0.78)	0.89 (0.73, 1.05)	0.52 (0.44, 0.60)
	12–14	1028	0.07 (0.05, 0.09)	0.17 (0.12, 0.22)	0.50 (0.33, 0.67)	0.72 (0.67, 0.76)	0.83 (0.73, 0.92)	0.48 (0.42, 0.55)
	15–17	985	0.07 (0.04, 0.10)	0.16 (0.11, 0.21)	0.47 (0.31, 0.63)	0.72 (0.66, 0.79)	0.88 (0.77, 0.99)	0.49 (0.43, 0.57)
	18–19	570	0.07 (0.04, 0.10)	0.19 (0.12, 0.27)	0.50 (0.36, 0.64)	0.72 (0.68, 0.77)	0.82 (0.75, 0.90)	0.49 (0.43, 0.54)
Male	All	4108	0.07 (0.04, 0.10)	0.17 (0.12, 0.23)	0.50 (0.35, 0.64)	0.72 (0.67, 0.76)	0.87 (0.74, 0.99)	0.50 (0.43, 0.57)
	<3	898	0.05 (0.09, 0.15)	0.10 (0.20, 0.48)	0.33 (0.63, 0.71)	0.67 (0.75, 0.85)	0.75 (0.95, 1.00)	0.49 (0.42, 0.56)
	3–5	627	0.07 (0.05, 0.09)	0.17 (0.12, 0.23)	0.50 (0.33, 0.68)	0.71 (0.65, 0.76)	0.82 (0.71, 0.94)	0.50 (0.42, 0.58)
	6–8	670	0.07 (0.05, 0.09)	0.14 (0.09, 0.19)	0.44 (0.27, 0.61)	0.71 (0.64, 0.77)	0.88 (0.76, 1.00)	0.53 (0.44, 0.61)
	9–11	607	0.07 (0.02, 0.12)	0.19 (0.09, 0.29)	0.49 (0.33, 0.65)	0.73 (0.67, 0.79)	0.82 (0.70, 0.95)	0.53 (0.54, 0.61)
	12–14	535	0.04 (0.01, 0.17)	0.09 (0.24, 0.50)	0.35 (0.64, 0.71)	0.67 (0.75, 0.88)	0.74 (1.02, 0.94)	0.48 (0.41, 0.56)
	15–17	495	0.04 (0.01, 0.19)	0.12 (0.26, 0.53)	0.39 (0.67, 0.73)	0.65 (0.81, 0.93)	0.75 (1.10, 1.00)	0.48 (0.42, 0.55)
	18–19	276	0.03 (0.01, 0.19)	0.10 (0.28, 0.53)	0.40 (0.66, 0.74)	0.68 (0.79, 0.90)	0.62 (1.18, 0.95)	0.49 (0.43, 0.56)
Female	All	3979	0.07 (0.04, 0.10)	0.18 (0.12, 0.24)	0.49 (0.35, 0.63)	0.71 (0.67, 0.76)	0.85 (0.75, 0.95)	0.49 (0.43, 0.56)
	<3	885	0.05 (0.09, 0.16)	0.10 (0.22, 0.47)	0.29 (0.65, 0.71)	0.66 (0.76, 0.86)	0.75 (0.96, 0.97)	0.49 (0.41, 0.58)
	3–5	560	0.07 (0.02, 0.12)	0.20 (0.12, 0.28)	0.51 (0.37, 0.66)	0.71 (0.66, 0.77)	0.85 (0.68, 1.03)	0.51 (0.42, 0.60)
	6–8	642	0.07 (0.04, 0.10)	0.18 (0.12, 0.25)	0.50 (0.33, 0.66)	0.71 (0.66, 0.75)	0.82 (0.72, 0.92)	0.48 (0.42, 0.55)
	9–11	616	0.07 (0.04, 0.10)	0.20 (0.13, 0.27)	0.48 (0.32, 0.64)	0.70 (0.63, 0.77)	0.88 (0.76, 1.01)	0.50 (0.42, 0.59)
	12–14	493	0.07 (0.05, 0.09)	0.16 (0.10, 0.22)	0.49 (0.34, 0.64)	0.72 (0.66, 0.78)	0.83 (0.74, 0.93)	0.48 (0.42, 0.56)
	15–17	490	0.07 (0.04, 0.10)	0.19 (0.11, 0.26)	0.50 (0.36, 0.65)	0.73 (0.66, 0.80)	0.88 (0.77, 0.99)	0.50 (0.41, 0.58)
	18–19	294	0.07 (0.06, 0.08)	0.19 (0.10, 0.28)	0.51 (0.34, 0.67)	0.71 (0.66, 0.76)	0.82 (0.74, 0.89)	0.48 (0.41, 0.55)

). Sex-stratified percentiles for males were 0.07 mg/L (95% CI: 0.04, 0.10) at the 10th, 0.50 mg/L (95% CI: 0.35, 0.64) at the 50th, and 0.87 mg/L (95% CI: 0.74, 0.99) at the 90th percentile. Median water fluoride for the females was 0.07 mg/L (95% CI: 0.04, 0.10), 0.49 mg/L (95% CI: 0.35, 0.63), and 0.85 mg/L (95% CI: 0.75, 0.95) at the 10th, 50th, and 90th percentiles, respectively. For all participants, the 90th percentile was 0.86 mg/L (95% CI: 0.75, 0.97).

The median urinary fluoride concentration among children and adolescents aged 6–19 years was 0.52 mg/L (95% CI: 0.48, 0.56) (

Table 2. Weighted quantiles (95% CIs) of urine fluoride concentrations (mg/L) in the NHANES (2015–2026) study population in persons 6–19 years of age.

	Age	N	10th Percentile	25th Percentile	50th Percentile	75th Percentile	90th Percentile	Mean
All	All	2408	0.18 (0.16, 0.21)	0.3 (0.27, 0.34)	0.52 (0.48, 0.56)	0.81 (0.72, 0.89)	1.15 (0.99, 1.32)	0.63 (0.57, 0.69)
	6–8	609	0.20 (0.15, 0.24)	0.33 (0.28, 0.39)	0.59 (0.50, 0.68)	0.92 (0.83, 1.02)	1.18 (1.05, 1.31)	0.67 (0.61, 0.73)
	9–11	582	0.20 (0.15, 0.26)	0.33 (0.27, 0.39)	0.53 (0.46, 0.60)	0.84 (0.69, 0.98)	1.25 (0.95, 1.56)	0.67 (0.61, 0.68)
	12–14	490	0.19 (0.12, 0.25)	0.30 (0.26, 0.35)	0.50 (0.46, 0.55)	0.77 (0.67, 0.86)	1.10 (0.96, 1.24)	0.58 (0.51, 0.63)
	15–17	471	0.17 (0.13, 0.21)	0.28 (0.24, 0.32)	0.46 (0.41, 0.51)	0.77 (0.66, 0.89)	1.13 (0.91, 1.36)	0.58 (0.55, 0.65)
	18–19	256	0.16 (0.10, 0.21)	0.29 (0.22, 0.36)	0.51 (0.42, 0.60)	0.77 (0.63, 0.91)	1.23 (0.75, 1.71)	0.64 (0.56, 0.70)
Male	All	1223	0.22 (0.19, 0.25)	0.35 (0.30, 0.39)	0.56 (0.51, 0.62)	0.87 (0.77, 0.98)	1.25 (1.05, 1.44)	0.68 (0.62, 0.75)
	6–8	311	0.22 (0.12, 0.31)	0.41 (0.31, 0.50)	0.68 (0.60, 0.75)	0.99 (0.89, 1.09)	1.29 (1.17, 1.41)	0.74 (0.67, 0.81)
	9–11	284	0.24 (0.19, 0.29)	0.38 (0.31, 0.45)	0.64 (0.54, 0.73)	0.91 (0.74, 1.08)	1.27 (0.84, 1.70)	0.73 (0.68, 0.79)
	12–14	259	0.20 (0.13, 0.28)	0.33 (0.26, 0.40)	0.53 (0.47, 0.58)	0.77 (0.62, 0.92)	1.12 (0.92, 1.33)	0.61 (0.55, 0.67)
	15–17	234	0.20 (0.17, 0.23)	0.31 (0.25, 0.37)	0.50 (0.45, 0.54)	0.80 (0.63, 0.97)	1.29 (0.71, 1.87)	0.64 (0.59, 0.71)
	18–19	135	0.21 (0.14, 0.29)	0.31 (0.22, 0.40)	0.55 (0.40, 0.70)	0.78 (0.62, 0.94)	1.38 (0.89, 1.87)	0.67 (0.62, 0.73)
Female	All	1185	0.16 (0.12, 0.20)	0.28 (0.24, 0.31)	0.46 (0.41, 0.50)	0.75 (0.66, 0.83)	1.11 (0.98, 1.25)	0.57 (0.51, 0.64)
	6–8	298	0.18 (0.15, 0.21)	0.30 (0.27, 0.33)	0.48 (0.41, 0.54)	0.81 (0.67, 0.94)	1.13 (1.06, 1.20)	0.60 (0.55, 0.66)
	9–11	298	0.17 (0.11, 0.23)	0.30 (0.22, 0.38)	0.45 (0.37, 0.53)	0.69 (0.53, 0.86)	1.17 (0.82, 1.51)	0.61 (0.52, 0.62)
	12–14	231	0.10 (0.04, 0.16)	0.26 (0.20, 0.31)	0.47 (0.41, 0.54)	0.75 (0.67, 0.83)	1.05 (0.82, 1.28)	0.55 (0.50, 0.58)
	15–17	237	0.15 (0.11, 0.18)	0.23 (0.18.0.28)	0.40 (0.32, 0.47)	0.69 (0.58, 0.80)	1.02 (0.84, 1.21)	0.53 (0.50, 0.57)
	18–19	121	0.10 (0.05, 0.15)	0.27 (0.18, 0.36)	0.50 (0.38, 0.62)	0.76 (0.50, 1.02)	1.12 (0.08, 2.16)	0.61 (0.53, 0.68)

). Fluoride levels were the highest in younger children, reaching 0.59 mg/L (95% CI: 0.50–0.68) in those aged 6–8 years, 0.53 mg/L (95% CI: 0.46–0.60) in those aged 9–11 years, 0.50 mg/L (95% CI: 0.46–0.55) at ages 12–14, 0.46 mg/L (95% CI: 0.41–0.51) at ages 15–17, and 0.51 mg/L (95% CI: 0.42–0.60) at ages 18–19. In sex-stratified analyses, males had consistently higher concentrations (0.56 mg/L, 95% CI: 0.51–0.62) compared with females (0.46 mg/L, 95% CI: 0.41–0.50), with the greatest sex differences observed in mid-childhood (ages 6–11). At the upper distribution, the 90th percentile reached 1.25 mg/L (95% CI: 1.05–1.44) in males and 1.11 mg/L (95% CI: 0.98–1.25) in females.

The median plasma fluoride concentration was 0.34 µmol/L (95% CI: 0.32, 0.36) among children and adolescents aged 6–19 years (

Table 3. Weighted quantiles (95% CIs) of plasma fluoride concentrations (umol/L) in the NHANES (2013–2014 & 2015–2016) study population in persons 6–19 years of age.

	Age	N	10th Percentile	25th Percentile	50th Percentile	75th Percentile	90th Percentile	Mean
All	All	4470	0.18 (0.14, 0.22)	0.26 (0.21, 0.30)	0.34 (0.32, 0.36)	0.47 (0.44, 0.49)	0.64 (0.60, 0.68)	0.40 (0.38, 0.43)
	6–8	1047	0.18 (0.14, 0.22)	0.28 (0.26, 0.30)	0.37 (0.33, 0.40)	0.50 (0.46, 0.53)	0.66 (0.63, 0.69)	0.43 (0.40, 0.45)
	9–11	1048	0.18 (0.14, 0.22)	0.26 (0.22, 0.31)	0.34 (0.32, 0.36)	0.47 (0.44, 0.50)	0.63 (0.57, 0.69)	0.40 (0.38, 0.43)
	12–14	926	0.18 (0.14, 0.22)	0.24 (0.20, 0.28)	0.32 (0.30, 0.33)	0.43 (0.40, 0.45)	0.57 (0.53, 0.62)	0.37 (0.34, 0.39)
	15–17	912	0.18 (0.14, 0.22)	0.18 (0.14, 0.22)	0.32 (0.30, 0.35)	0.47 (0.42, 0.51)	0.64 (0.60, 0.69)	0.40 (0.37, 0.43)
	18–19	537	0.18 (0.13, 0.23)	0.27 (0.22, 0.33)	0.36 (0.32, 0.40)	0.49 (0.43, 0.55)	0.72 (0.59, 0.84)	0.44 (0.38, 0.49)
Male	All	2280	0.18 (0.14, 0.22)	0.27 (0.25, 0.28)	0.35 (0.33, 0.37)	0.48 (0.45, 0.50)	0.65 (0.60, 0.70)	0.41 (0.37, 0.44)
	6–8	551	0.18 (0.14, 0.22)	0.29 (0.26, 0.31)	0.38 (0.34, 0.42)	0.51 (0.48, 0.54)	0.68 (0.62, 0.73)	0.45 (0.41, 0.48)
	9–11	522	0.18 (0.14, 0.22)	0.28 (0.27, 0.30)	0.36 (0.34, 0.38)	0.49 (0.45, 0.52)	0.65 (0.59, 0.71)	0.42 (0.37, 0.45)
	12–14	484	0.18 (0.14, 0.22)	0.26 (0.21, 0.30)	0.33 (0.30, 0.35)	0.44 (0.40, 0.48)	0.60 (0.52, 0.67)	0.38 (0.33, 0.42)
	15–17	457	0.18 (0.14, 0.22)	0.18 (0.14, 0.22)	0.32 (0.29, 0.36)	0.45 (0.41, 0.50)	0.62 (0.56, 0.67)	0.39 (0.34, 0.45)
	18–19	266	0.18 (0.13, 0.23)	0.28 (0.23, 0.33)	0.37 (0.32, 0.41)	0.49 (0.40, 0.58)	0.73 (0.53, 0.92)	0.44 (0.38, 0.46)
Female	All	2190	0.18 (0.14, 0.22)	0.24 (0.20, 0.28)	0.33 (0.30, 0.35)	0.46 (0.43, 0.49)	0.63 (0.58, 0.68)	0.39 (0.35, 0.44)
	6–8	496	0.20 (0.13, 0.23)	0.28 (0.22, 0.33)	0.36 (0.32, 0.39)	0.49 (0.43, 0.54)	0.64 (0.60, 0.68)	0.40 (0.36, 0.44)
	9–11	526	0.20 (0.14, 0.22)	0.20 (0.16, 0.24)	0.32 (0.29, 0.35)	0.44 (0.41, 0.47)	0.61 (0.53, 0.69)	0.38 (0.32, 0.41)
	12–14	442	0.18 (0.02, 0.14)	0.22 (0.18, 0.14)	0.22 (0.30, 0.28)	0.32 (0.42, 0.39)	0.45 (0.55, 0.50)	0.60 (0.53, 0.64)
	15–17	455	0.18 (0.02, 0.14)	0.22 (0.18, 0.14)	0.22 (0.32, 0.29)	0.35 (0.48, 0.43)	0.53 (0.65, 0.56)	0.74 (0.67, 0.82)
	18–19	271	0.18 (0.02, 0.13)	0.23 (0.25, 0.20)	0.30 (0.35, 0.30)	0.40 (0.49, 0.42)	0.56 (0.68, 0.53)	0.83 (0.72, 0.89)

). Age-specific medians were slightly higher in younger children, 0.37 µmol/L (95% CI: 0.33–0.40) at ages 6–8 years, 0.34 µmol/L (95% CI: 0.32–0.36) at ages 9–11, 0.32 µmol/L (95% CI: 0.30–0.33) at ages 12–14, 0.32 µmol/L (95% CI: 0.30–0.35) at ages 15–17, and 0.36 µmol/L (95% CI: 0.32–0.40) in those aged 18–19. Sex-stratified medians were 0.35 µmol/L (95% CI: 0.33, 0.37) in males and 0.33 µmol/L (95% CI: 0.30, 0.35) in females. The 90th percentile was 0.65 µmol/L (95% CI: 0.60, 0.70) for males, 0.63 µmol/L (95% CI: 0.58, 0.68) for females, and 0.64 µmol/L (95% CI: 0.60, 0.68) for all participants.

99.96% (8084/8087) of children were within the EPA-enforced limit of 4.0 mg/L, while 99.05% (8010) were within the USEPA non-enforced limit of 2.0 mg/L, and 98.58% (7922/8087) were within the WHO-recommended limit of 1.5 mg/L of water fluoride (

Table 4. Water Fluoride levels, based on different Governing bodies.

Characteristics	EPA Enforced			EPA Non Enforced
	≤4	>4	p-Value	≤2	>2	p-Value	≤1.5	>1.5	p-Value
Overall	8084 (99.96)	3 (0.04)	−−	8010	77	−−	7922 (98.58)	164 (1.42)
Age 0–5 6 to 9 10 to 12 13 to 16 17 to 19	2970 (29.11) 1717 (20.25) 1157 (15.38) 1383 (21.97) 857 (13.29)	0 0 1 2 0	−−−	2935 (28.86) 1698 (20.09) 1144 (15.26) 1377 (21.90) 856 (13.27)	35 (0.24) 19 (0.15) 14 (0.13) 8 (0.08) 1 (0.01)	0.0038	2906 (28.63) 1680 (19.91) 1128 (15.09) 1365 (21.78) 844 (13.17)	64 (0.46) 37 (0.33) 30 (0.30) 20 (0.21) 13 (0.12)	0.0868
Male	4105 (51.07)	3 (0.02)	−−−	4066 (50.72)	42 (0.38)	0.0314	4021 (50.32)	87 (0.78)	0.3305
Race Black Hispanic White	1894 (13.77) 2705 (24.17) 2219 (51.49)	2 (0.02) 0 1 (0.02)	−−−	1894 (13.77) 2638 (23.69) 2213 (51.40)	2 (0.02) 67 (0.48) 7 (0.11)	<0.0001	1886 (13.71) 2589 (23.30) 2197 (51.13)	10 (0.08) 116 (0.87) 23 (0.38)	<0.0001
Annual household Income 10,000 to 24,999 25,000 to 54,999 55,000 to 74,999 75,000 to 99,999	1602 (16.05) 1345 (26.63) 2343 (27.82) 778 (11.72)	1 (0.01) 0 1 (0.01) 1 (0.01)		1598 (16.02) 1342 (26.61) 2316 (27.59) 757 (11.52)	5 (0.04) 3 (0.02) 28 (0.25) 22 (0.22)	<0.0001	1588 (15.91) 1330 (26.47) 2279 (27.23) 749 (11.42)	15 (0.15) 15 (0.17) 65 (0.61) 30 (0.31)	<0.0001
Born in the US	7567 (95.09)	3 (0.04)		7499 (94.56)	71 (0.56)	0.4634	7418 (93.79)	152 (1.33)	0.5775
Length of time in the US less than one year 1 to <5 years 5 to <10 10 to <15	86 (14.98) 179 (36.31) 115 (23.56) 81 (17.44)		−−−	84 (14.68) 179 (36.31) 112 (22.89) 81 (17.44)	2 (0.30) 3 (0.67)	−−−	84 (14.68) 178 (36.18) 109 (22.49) 80 (17.27)	2 (0.30) 1 (0.13) 6 (0.107) 1 (0.17)	0.0608
Have serious difficulty hearing	70 (0.90)	0	−−−	70 (0.90)	0	−−−	70 (0.90)	0	−−−
Have serious difficulty seeing	132 (1.63)	0	−−−	131 (1.62)	1 (0.01)	0.6556	130 (0.161)	2 (0.02)	0.7623
Have serious difficulty concentrating	618 (11.47)	0	−−−	616 (11.45)	2 (0.02)	0.1193	606 (11.32)	12 (0.15)	0.9373
Covered by Health Insurance	7442 (92.67)	2 (0.03)	0.1071	7375 (92.14)	69 (0.56)	0.7165	7294 (91.40)	150 (0.130)	0.7014
General health condition Excellent Very Good Good Fair Poor	375 (15.65) 884 (40.76) 906 (33.83) 270 (8.76) 32 (0.95)	1 (0.02) 1 (0.02) 0 0	−−−	373 (15.59) 880 (40.66) 904 (33.77) 269 (8.74) 32 (0.95)	2 (0.05) 5 (0.13) 3 (0.09) 0 5 (0.13)	−−−	369 (15.47) 870 (40.42) 894 (33.55) 268 (8.71) 32 (0.95)	6 (0.17) 15 (0.37) 13 (0.31) 2 (0.06) 0	−−−
Mother’s age when born 14 years or younger 15 to 19 20 to 25 26 to 35 36 to 44 45 or more	16 (0.21) 752 (9.15) 2105 (28.84) 3190 (51.11) 681 (10.46) 17 (0.21)	0 0 0 1 (0.02) 0 0	−−−	15 (0.20) 740 (9.04) 2085 (28.63) 3157 (50.79) 676 (10.42) 17 (0.21)	1 (0.01) 12 (0.11) 20 (0.20) 34 (0.34) 5 (0.04) 0	−−−	15 (0.20) 729 (8.94) 2057 (28.28) 3132 (50.47) 669 (10.36) 17 (0.21)	1 (0.01) 23 (0.21) 48 (0.55) 59 (0.66) 12 (0.10) 0	−−−
Mother smoked when pregnant	649 (10.60)	2 (0.03)	−−−	646 (10.57)	5 (0.06)	0.6075	642 (10.49)	9 (0.14)	0.799
Weight at birth, pounds 3 pounds of less 4 to 6 pounds 7 to 10 pounds 11 pounds or more	120 (1.53) 2452 (34.37) 4037 (63.85) 18 (0.22)	0 0 2 (0.03) 0	−−−	116 (1.49) 2425 (34.13) 3999 (63.44) 18 (0.22)	4 (0.04) 27 (0.23) 40 (0.44) 0	−−−	113 (1.47) 2408 (33.94) 3952 (62.86) 18 (0.22)	7 (0.06) 44 (0.42) 87 (1.02) 0	−−−
Child food security category full or marginal: 0 CH marginal: 1 CH low: 2–4 CH very low 5–8	6204 (83.35) 605 (6.33) 788 (8.60) 148 (1.68)	3 (0.04) 0 0 0	−−−	6151 (82.91) 603 (6.32) 776 (8.50) 141 (1.63)	56 (0.48) 2 (0.01) 12 (0.10) 7 (0.05)	0.0653	6075 (82.18) 596 (6.23) 774 (8.49) 141 (1.63)	132 (1.21) 9 (0.10) 14 (0.11) 7 (0.05)	0.7116
Food Stamp Benefit	4007 (41.36)	1 (0.02)	0.9559	3970 (41.09)	38 (0.28)	0.4022	3925 (40.62)	83 (0.76)	0.1784

−−− sample too small to calculate p value.

). Although statistically significant differences were observed across sociodemographic categories, the proportion of children exceeding the upper fluoride thresholds was extremely low. Significant subgroup differences emerged under the lower, non-enforceable standards. For the EPA 2.0 mg/L guideline, exceedances differed by age (p = 0.0038), sex (p = 0.0314), and race/ethnicity (p < 0.0001). For the WHO 1.5 mg/L guideline, exceedances also varied significantly by race/ethnicity (p < 0.0001) and household income (p < 0.0001).

According to CDC urine fluoride categories, 11.77% (289/2408) of the children had urine fluoride < 0.2 mg/L, 88.06% (2114/2408) had 0.2–<3.2 mg/L, and 0.17% (5) had ≥3.2 mg/L (

Table 5. Plasma fluoride concentrations (µmol/L) and urinary fluoride concentrations (mg/L).

Characteristics	Urine(mg/L) (CDC)					Plasma Fluoride (µmol/L) (Mayo Clinic)
	<0.02	0.2–<3.2	≥3.2	p-value	<1	≥1–4	p-value
Overall	29 (11.77)	2114 (88.06)	5 (0.17)		4370 (97.53)	100 (2.47)
Age 6 to 9 10 to 12 13 to 16 17 to 19	79 (2.75) 58 (2.30) 100 (4.67) 52 (2.06)	720 (24.39) 486 (19.13) 561 (28.56) 347 (15.99)	3 (0.06) 2 (0.10) 0 0	−−−	1348 (25.01) 997 (21.13) 1236 (31.37) 789 (20.02)	31 (0.58) 19 (0.42) 26 (0.82) 24 (0.65)	0.6247
Male	112 (3.38)	1109 (47.07)	2 (0.11)	<0.0001	2225 (50.34)	55 (1.47)	0.2324
Race Black Hispanic White	34 (0.80) 103 (3.02) 85 (6.22)	498 (12.81) 756 (21.30) 555 (45.53)	3 (0.06) 0 1 (0.08)	−−−	1015 (12.99) 1567 (24.31) 1138 (50.78)	16 (0.20) 31 (0.47) 35 (1.57)	0.3064
Annual household Income 0 to 9999 10,000 to 24,999 25,000 to 54,999 55,000 to 74,999 75,000 to 99,999 100,000 or more	16 (0.50) 36 (1.32) 59 (3.95) 101 (3.72) 31 (1.22) 23 (1.16)	132 (3.83) 338 (10.87) 349 (24.59) 624 (23.73) 261 (12.52) 204 (12.40)	1 (0.02) 1 (0.02) 1 (0.09) 0 1 (0.02) 1 (0.02)	−−−	282 (4.58) 819 (14.35) 728 (26.42) 1365 (28.90) 434 (11.67) 381 (11.63)	7 (0.12) 12 (0.28) 23 (0.81) 29 (0.61) 11 (0.36) 9 (0.27)	0.8202
Born in US	252 (10.77)	1938 (82.91)	5 (0.17)	−−−	3987 (91.65)	93 (2.31)	0.9295
Length of time in US 1 to <5 years 5 to <10 years 10 to <15 years >15 years	9 (4.88) 9 (3.44) 8 (3.41) 5 (2.55)	59 (30.29) 47 (20.63) 27 (15.44) 10 (7.64)	−−−	0.761	120 (31.45) 98 (26.45) 74 (21.17) 25 (7.97)	1 (0.26) 1 (0.19) 3 (1.97)	−−−
Disability
Have serious difficulty hearing	3 (0.16)	20 (0.64)	0		46 (0.98)	0
Have serious difficulty seeing	7 (0.24)	52 (1.78)	0		110 (2.02)	3 (0.08)	0.4334
Have serious difficulty concentrating	23 (1.11)	281 (12.01)	0		512 (11.82)	8 (0.14)	0.0221
Covered by Health Insurance	250 (10.50)	1929 (81.78)	5 (0.17)		3929 (89.21)	88 (2.23)	0.6445
General health condition Excellent Very Good Good Fair Poor	30 (2.36) 56 (4.76) 51 (3.62) 20 (1.46) 2 (0.10)	166 (15.91) 349 (34.69) 358 (28.75) 111 (7.45) 13 (0.91)		0.7508	336 (15.20) 791 (39.31) 838 (33.69) 246 (8.42) 31 (0.97)	2 (0.12) 19 (1.16) 25 (0.92) 3 (0.13) 1 (0.08)	0.2924
Mother’s age when born 14 years or younger 15 to 19 20 to 25 26 to 35 36 to 44 45 or more	0 17 (0.80) 63 (3.34) 102 (5.84) 23 (1.33) 0	8 (0.3) 215 (9.22) 535 (27.89) 711 (43.53) 117 (7.36) 4 (0.15)	0 0 1 (0.03) 3 (0.17) 1 (0.03) 0	−−−	11 (0.30) 403 (9.85) 1064 (30.26) 1443 (48.97) 258 (8.41) 9 (0.15)	0 7 (0.15) 22 (0.86) 32 (0.94) 3 (0.12) 0	−−−
Mother smoked when pregnant	19 (1.13)	153 (9.52)	0	−−−	318 (11.55)	5 (0.12)	0.0112
Weight at birth, pounds 3 pounds of less 4 to 6 pounds 7 to 10 pounds 11 pounds or more	3 (0.18) 62 (3.27) 133 (7.71) 1 (0.09)	37 (1.86) 621 (33.98) 881 (52.42) 5 (0.26)	0 1 (0.03) 4 (0.21) 0	−−−	54 (1.44) 1129 (33.21) 1904 (62.99) 10 (0.26)	1 (0.02) 13 (0.33) 49 (1.75) 0	−−−
Child food security full or marginal: 0 marginal: 1 low: 2–4	205 (9.42) 17 (0.67) 27 (0.99)	1475 (69.36) 170 (6.11) 274 (10.57)	4 (0.15) 1 (0.02) 0	−−−	3152 (79.72) 330 (6.14) 495 (9.57)	69 (1.89) 4 (0.06) 16 (0.29)	0.5661
Food Stamp Benefit	122 (4.49)	1150 (40.67)	1 (0.02)	0.0046	2200 (40.93)	38 (0.73)	0.1141

−−− sample too small to calculate p value.

). Males were significantly more likely than females to be in higher urinary fluoride categories (p < 0.0001). Receipt of food stamp benefits was associated with a small but statistically significant shift in urinary fluoride distributions (p = 0.0046). According to Mayo Clinic plasma fluoride categories, 97.53% (4370/4470) of children had plasma fluoride <1 µmol/L, and 2.47% (100/4470) had ≥1–4 µmol/L. Children whose mothers smoked during pregnancy had a higher likelihood of being above the Mayo Clinic threshold (p = 0.0112), and children reported to have serious difficulty concentrating also showed a higher prevalence (p = 0.0221). Despite these statistically significant associations, the proportion of participants in the upper exposure categories remained very small across all groups.

4. Discussion

We found that most children had fluoride exposure within recommended thresholds across all biomarkers. Drinking water concentrations were almost universally below the enforceable standard set by the USEPA, the non-enforceable guideline, and the WHO guideline. Plasma fluoride levels were overwhelmingly under the Mayo Clinic’s clinical threshold, and urinary fluoride values generally fell within the CDC’s reference ranges [12,24]. These findings suggest that, at the population level, U.S. children are not experiencing excessive fluoride exposure based on the current regulatory agencies’ recommendations. However, subgroup analyses did reveal significant differences by sex in urinary fluoride, as well as associations with maternal smoking and cognitive difficulty in plasma fluoride categories, underscoring the importance of monitoring vulnerable populations even when overall exposure is low. Public water fluoridation was widespread in the eastern U.S. but less common in many western states, and overlays of groundwater data indicate that fluoridation tends to be implemented where groundwater levels are low, while regions with higher groundwater levels rarely add fluoride in public water.

Median water fluoride concentrations were very consistent across age and sex groups. This stability likely reflects the fact that household tap water fluoride levels are determined primarily by community water fluoridation practices and naturally occurring fluoride in source water, both of which are not strongly influenced by individual characteristics [4,26]. Hence, fluoride concentrations are a random variable that is independent of individual-level characteristics.

In contrast, urinary fluoride varied more by age, with the highest medians in younger children (6–8 years) and lower levels in early adolescence (12–14 years). Urinary fluoride varied more by age: medians were highest in children aged 6–8 years and lowest for 12–14 years. This age-related pattern likely reflects higher water consumption relative to body weight among younger children, as well as greater unintentional ingestion of fluoride-containing dental products such as toothpaste during early childhood [27]. Sex differences for urinary fluoride levels were more pronounced: males had a higher median (0.56 mg/L) compared with females (0.46 mg/L), and this gap was most evident in mid-childhood (ages 6–11). This difference may be explained by higher water and caloric beverage intake among boys compared to girls, as documented in dietary surveys, as well as potential sex-specific differences in fluoride metabolism and renal excretion [28,29].

Age differences for plasma fluoride were modest: younger children (6–8 years: 0.37 µmol/L) had slightly higher medians than older adolescents (15–17 years: 0.32 µmol/L). This pattern likely reflects younger children’s greater fluoride intake relative to body weight and possible developmental differences in renal clearance during growth [18]. Males had slightly higher concentrations compared with females. Previous studies have reported that boys generally consume larger volumes of water and caloric beverages than girls, which could contribute to their higher urinary fluoride concentrations, and biological differences in renal handling of fluoride may also play a role [30,31].

Our geographic analyses revealed that groundwater fluoride levels vary substantially across the United States, with large regions of the Northeast, Midwest, and Southeast exhibiting very low concentrations (<0.2 mg/L) (Figure 1). In contrast, higher concentrations (>1.5 mg/L) were localized to parts of Texas, Arizona, and Idaho. Public water fluoridation coverage was extensive in the eastern U.S. but limited in many western States (Figure 2) [23]. Importantly, the overlay of Figure 1 and Figure 2 demonstrated that fluoridation policies tend to align with natural conditions: counties with naturally low groundwater fluoride were more likely to implement fluoridation, while regions with elevated natural levels rarely added supplemental fluoride [31]. Nevertheless, several Western counties showed both low natural fluoride and limited fluoridation coverage. These regional gaps highlight opportunities to strengthen public health policy, particularly in western states where population needs and infrastructure constraints intersect [4,23].

This study is strengthened by its use of nationally representative NHANES data combined with U.S. Geological Survey and CDC databases, allowing for a comprehensive assessment of fluoride exposure across multiple biological matrices and geographies. The integration of individual biomarker data with community-level water policies offers a unique perspective on both biomarkers of exposure and structural determinants of fluoride intake. Limitations include the cross-sectional nature of NHANES, which precludes causal inference, and reliance on spot urine and plasma samples, which may not fully capture long-term exposure variability [32]. Additionally, community-level data does not always reflect household water sources, particularly in rural areas relying on private wells [33].

This study provides important national-level evidence that fluoride exposure among U.S. children remains largely within recommended thresholds. From a public health perspective, the alignment between low natural groundwater fluoride levels and higher fluoridation coverage suggests policy responsiveness. However, challenges remain, including regional gaps in fluoridation coverage, lack of biomonitoring for children under six in urine/plasma datasets, and continued misinformation surrounding fluoridation safety. Future research should incorporate longitudinal biomarker data, assess developmental outcomes related to chronic low-level exposure, and evaluate equity gaps in access to optimally fluoridated water. Integration of environmental, behavioral, and clinical datasets will be essential for establishing more precise fluoride guidelines for vulnerable age groups.

5. Conclusions

In conclusion, based on our findings, we recommend that fluoride exposure among U.S. children generally remains within thresholds established by major regulatory and clinical bodies, including the EPA, CDC, WHO, and Mayo Clinic. However, to further improve whether these standards adequately protect vulnerable subgroups, future research should incorporate longitudinal designs that track fluoride exposure trajectories alongside developmental and health outcomes. Additionally, integrating geospatial data with biomarker measures will be essential for identifying local disparities and informing targeted, community-level interventions. Strengthening national surveillance systems to monitor fluoride biomarkers routinely may further enhance early detection of potential over- or under-exposure. Finally, these efforts will support evidence-based policies aimed at optimizing fluoride benefits while minimizing risks for all children.