Abstract

This retrospective practice audit explored iodine deficiency and halide levels in Brevard County, Florida, using patient data from Iron Direct Primary Care. The study analyzed random urine iodine concentrations from a combined cohort (N=116, excluding known high exogenous intake), serum iodine levels (N=49), and iodine challenge tests (N=36). The median urinary iodine concentration (UIC) for the non-exogenous cohort was 88.8 µg/L, indicating mild iodine deficiency by WHO standards. Overall, 57.8% of this cohort exhibited UIC below the WHO’s adequate threshold of 100 µg/L, with varying degrees of deficiency. Serum iodine analysis (N=49) revealed a median value of 46.6 µg/L, suggesting low iodine status. All 36 participants in the iodine challenge test excreted less than 90% of a 50mg iodine dose (mean excretion 63.0%), suggesting widespread iodine insufficiency and showing evidence of fluoride and bromide displacement. Gender-specific analysis of non-exogenous random urine iodine levels showed no statistically significant difference in mean concentrations between males and females (p=0.341). The study underscores the need for public health interventions, including consideration of iodine supplementation strategies and halide competition in assessing iodine status. The findings advocate for increased awareness to combat health risks associated with iodine deficiency and support public health policy interventions to limit exposure to iodine receptor competitors fluoride and bromide that the WHO standards for iodine sufficiency are too low.

Introduction

 Iodine, indispensable for thyroid hormone production, influences metabolism, growth, and neurodevelopment (Bonofiglio & Catalano, 2020). Despite the importance of maintaining optimal levels of iodine, iodine deficiency remains prevalent, potentially causing health issues such as goiter, hypothyroidism, developmental delays, fibrocystic breast diseases, and an increased risk of cancerous growths of the breast, thyroid, uterus, and prostate (Zimmerman et al., 2009). Moreover, comprehensive epidemiological data on iodine status within regions of the U.S. population have been relatively scarce since foundational national surveys such as those reported by Hollowell et al. (1998), highlighting the ongoing need for contemporary regional assessments. This study evaluated iodine status by analyzing results from random urine iodine tests, serum iodine tests, and iodine challenge tests from patients at a primary care practice in Brevard County, Florida, to determine the prevalence of iodine deficiency and explore halide interactions, discussing the implications for public health.

Methods

This study was conducted as a retrospective practice audit at Iron Direct Primary Care in Brevard County, Florida. Data were analyzed from patients who had undergone random urine iodine testing (LabCorp), serum iodine testing (LabCorp), and/or urine halide challenge testing (Doctors Data) between May 2021 and December 2024.

Results

Urinary Iodine Concentrations (Non-Exogenous Combined Cohort, N=116):
Analysis of the combined random and pre-challenge spot urine iodine samples (N=116), after excluding two presumed exogenous users (UIC > 600 µg/L), yielded the following:
Mean UIC: 121.91 µg/L
Median UIC: 88.8 µg/L
Standard Deviation: 98.23 µg/L
Range: 0.0 µg/L to 446.5 µg/L
IQR: 62.45 µg/L (25th percentile) to 150.95 µg/L (75th percentile). The median UIC of 88.8 µg/L indicates mild iodine deficiency in this cohort according to WHO standards.

Distribution of Iodine Levels (Non-Exogenous Combined Cohort, N=116) per WHO standards:
Severe Deficiency (<20 µg/L): 4 samples (3.4%)
Moderate Deficiency (20-49 µg/L): 21 samples (18.1%)
Mild Deficiency (50-99 µg/L): 42 samples (36.2%)
Total with Deficiency (100 µg/L): 67 samples (57.8%)
Adequate (100-199 µg/L): 24 samples (20.7%)
More than Adequate (200-600 µg/L): 25 samples (21.6%)

Gender Analysis (Non-Exogenous Combined Cohort Urine Iodine):
This dataset included 42 males and 41 females with available gender information.
Mean Iodine Males (N=42): 95.79 µg/L
Mean Iodine Females (N=41): 115.44 µg/L A two-sample t-test found no statistically significant difference in mean urine iodine concentrations between males and females (t = -0.958, p = 0.341; Levene test p=0.515).

Serum Iodine (N=49):
Mean Serum Iodine: 48.64 µg/L
Median Serum Iodine: 46.6 µg/L
Standard Deviation: 14.52 µg/L
Range: 27.5 µg/L to 107.0 µg/L
IQR: 40.8 µg/L to 52.9 µg/L

Iodine Challenge Test (N=36):
All 36 participants excreted less than 90% of the 50mg iodine/iodide load over 24 hours, indicating iodine insufficiency.
Mean Iodine Excretion: 63.0%
Median Iodine Excretion: 65.0%
Standard Deviation: 10.27%
Range: 44.0% to 80.0%

Pre-Challenge Urine Halides (N=36 cohort):
Iodine (N=35 valid pre-test samples):
Mean UIC: 182.7 µg/L (after conversion from µg/mL)
Median UIC: 140.0 µg/L (Note: This specific subgroup analysis for pre-challenge iodine includes individuals who might be on exogenous iodine; one patient had a pre-challenge value of 1800 µg/L).

Bromine (µg/mL, N=34 valid data):
Mean: 2.50; Median: 1.85; SD: 1.88; Range: 0.28 – 7.4

Fluoride (µg/mL, N=34 valid data):
Mean: 0.57; Median: 0.52; SD: 0.29; Range: 0.2 – 1.2

Post-Challenge Urine Halides (N=36 cohort):
Bromine (mg/24 hr, N=34 valid data):
Mean: 3.57; Median: 2.75; SD: 2.29; Range: 1.1 – 11.0

Fluoride (mg/24 hr, N=33 valid data):
Mean: 0.90; Median: 0.7; SD: 0.61; Range: 0.28 – 3.5. Observation of pre- and post-challenge halide levels suggests displacement occurred

Discussion

 This retrospective practice audit conducted in Brevard County, Florida, provides significant insights into local iodine nutritional status and the potential impact of competing halides. The analysis of 116 spot/random urine samples (excluding individuals with high exogenous iodine intake) revealed a median urinary iodine concentration (UIC) of 88.8 µg/L. This central tendency positions the studied cohort within the mild iodine deficiency range according to World Health Organization (WHO) criteria (WHO, 2024). Critically, 57.8% of these individuals exhibited UIC levels below the 100 µg/L threshold, indicating that a majority may not be achieving iodine adequacy. These findings are noteworthy and align with broader concerns about iodine status, as highlighted by research from Zimmerman et al. (2009) and Caldwell et al. (2011), which documented trends of suboptimal iodine levels even within developed nations.

Further supporting these observations, serum iodine data from 49 participants showed a median of 46.6 µg/L, indicative of low iodine status in this group, although serum iodine is recognized as a less sensitive measure for population assessment compared to UIC. The investigation into gender-based differences in non-exogenous urine iodine revealed no statistically significant disparity in mean UIC between males and females (p=0.341), suggesting that the observed patterns of iodine insufficiency are prevalent across genders within this patient sample.

The Iodine Challenge Test, performed on 36 participants, offered compelling evidence of iodine insufficiency. This test evaluates iodine status by quantifying the 24-hour urinary excretion of a 50mg oral iodine/iodide load; lower excretion (typically <90%) signifies bodily retention due to need. Strikingly, all 36 participants in this study excreted less than 90% of the administered dose, with a mean excretion of only 63.0%. Such universal retention underscores a widespread physiological demand for iodine among these individuals.

A key aspect of the Iodine Challenge Test is its utility in elucidating competitive halide dynamics. Following iodine loading, an increased urinary output of both bromide (mean pre-challenge 2.50 µg/mL vs. mean post-challenge 3.57 mg/24 hr) and fluoride (mean pre-challenge 0.57 µg/mL vs. mean post-challenge 0.90 mg/24 hr) was observed. While differences in pre- and post-challenge units make direct quantitative comparison of excretion rates challenging without pre-challenge 24-hour urine volumes, the pattern of increased halide detection in 24-hour post-load urine is suggestive of displacement by iodine. This finding is consistent with established mechanisms whereby halogens like fluoride and bromide competitively inhibit iodine uptake, particularly at the sodium-iodide symporter (NIS) in the thyroid gland, potentially impairing thyroid function (Waugh, 2019). The presence of these halides could therefore exacerbate existing iodine deficiencies or functionally increase an individual’s iodine requirement. This is particularly relevant given contemporary environmental exposures and local public health discussions, such as those concerning water fluoridation policies in Florida. Literature, such as the study by Kheradpisheh et al. (2018), has also indicated a negative impact of fluoride on thyroid hormone parameters even at standard concentrations.

Clinical observations from this primary care setting suggest that iodine supplementation, often at doses exceeding the standard RDA (e.g., 6-12mg daily or higher), is frequently well-tolerated and associated with patient-reported improvements in conditions sometimes linked to iodine deficiency, such as fibrocystic breast symptoms (Ghent et al., 1993), fatigue, and cognitive difficulties. These clinical experiences, while anecdotal to this audit, underscore the perceived importance of addressing iodine insufficiency. The occasional report of transient symptoms during initial iodine supplementation, possibly related to halide mobilization, is an area that merits further systematic investigation. The adjunctive use of selenium is often considered in iodine repletion protocols, reflecting its crucial roles in thyroid hormone conversion and antioxidant protection within the thyroid gland (Negro et al., 2007; Wichman et al., 2016).

The findings of widespread deficiency and insufficiency in a patient population reportedly consuming RDA levels of iodine lend credence to the hypothesis that current RDAs (e.g., 150 µg/day for most adults) may not be adequate for all individuals, particularly in environments with notable exposure to competing halides that can impair iodine absorption or utilization, as theorized by Waugh (2019).

The prevalence of iodine deficiency and insufficiency identified in this Brevard County cohort has notable public health implications. Iodine’s essentiality extends beyond thyroid hormone synthesis to encompass broad roles in metabolic regulation, neurodevelopment (critically for fetal and early childhood stages), and potentially in mitigating risks for certain hormone-sensitive cancers (Zimmerman et al., 2009; Bonofiglio & Catalano, 2020). These results highlight a need for enhanced awareness among healthcare providers and the public regarding optimal iodine nutrition. Potential strategies could involve dietary counseling, more targeted approaches to iodine supplementation (especially where halide exposure is a factor), and ongoing surveillance of iodine status within the community. The data also support broader public health considerations aimed at minimizing exposure to unnecessary environmental halides.

Acknowledgments

Stefan Hartmann extracted the lab values and was the primary author of the manuscript.
Isabella Hartmann contributed to the literature review and statistical analysis.
Pierre Cloutier offered guidance on the overall format and provided his extensive knowledge on the role of the elements and their role in human physiology.

References