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Impact of high iodine and fluoride intake on children’s IQ in rural China.
| European Journal of Nutrition | Xia Y, Ye Y, Liu M, Wang Y, Shang L, Wang P, Sun H. | 64(2):104.
China-IQ Iodine IQ Score Urine-F Human Study

Abstract

Background

Excessive intake of both fluorine and iodine can lead to various health effects. The potential influence of excessive fluorine and iodine intake on the intelligence of school-age children has become a notable concern.

Objectives

To investigate the relationship between urinary fluoride (UF) levels, urinary iodine (UI) levels, and intelligence quotient (IQ).

Methods

This study involved 711 children aged 8 to 12 from rural Jiangsu, China. Water iodine levels were measured using As3+-Ce4+ catalytic spectrophotometry, while UI levels were determined using inductively coupled plasma mass spectrometry. Fluoride levels in urine and drinking water were measured using the ion-selective electrode method. Children’s cognitive function, evaluated through IQ scores, was assessed using the Combined Raven’s Test. The results were considered significant at the P <0.05 level.

Results

The average IQ score was 107.6, the median UF was 281 µg/L, and the median UI was 1.39 mg/L. The correlation coefficient (B) and confidence interval (95%CI) for UF and UI on IQ were -3.34 (-4.14, -2.43) and -3.31 (-4.19, -2.41), respectively (P<0.001, P<0.001). UF>1.4 mg/L and UI>300 µg/L were negatively correlated with IQ scores in all school-age children (P<0.001, P<0.001), with B and 95% CIs of -3.59 (-5.45, -1.74), -4.06 (-5.91, -2.21), respectively. The interaction term (UF> 1.4 mg/L: UI >300 µg/L) was negatively correlated with IQ scores in all (P=0.041) and female school-age children (P=0.007), with B and 95%CIs of -4.43 (-8.66, -0.19) and -8.87 (-15.16, -2.40), respectively.

Conclusions

High levels of both fluoride and iodine intake negatively affect the IQ of school-age children. Monitoring and regulating these elements in children’s diets is essential to prevent cognitive impairment.

ABSTRACT ONLINE AT https://link.springer.com/article/10.1007/s00394-025-03617-w

References

  1. Jha SK, Singh RK, Damodaran T, et al (2013) Fluoride in Groundwater: Toxicological Exposure and Remedies. Journal of Toxicology and Environmental Health, Part B 16:52–66. https://doi.org/10.1080/10937404.2013.769420

  2. He X, Li P, Ji Y, et al (2020) Groundwater Arsenic and Fluoride and Associated Arsenicosis and Fluorosis in China: Occurrence, Distribution and Management. Expo Health 12:355–368. https://doi.org/10.1007/s12403-020-00347-8

  3. Shyam R, Bhadravathi Chaluvaiah M, Kumar A, et al (2020) Impact of dental fluorosis on the oral health related quality of life among 11- to 14-year-old school children in endemic fluoride areas of Haryana (India). International Dental Journal 70:340–346. https://doi.org/10.1111/idj.12567

  4. Augustsson A, Berger T (2014) Assessing the risk of an excess fluoride intake among Swedish children in households with private wells — Expanding static single-source methods to a probabilistic multi-exposure-pathway approach. Environment International 68:192–199. https://doi.org/10.1016/j.envint.2014.03.014

  5. Choi AL, Sun GF, Zhang Y, Grandjean P (2012) Developmental Fluoride Neurotoxicity: A Systematic Review and Meta-Analysis. Environmental Health Perspectives 120:1362–1368. https://doi.org/10.1289/ehp.1104912

  6. Yani SI, Seweng A, Mallongi A, et al (2021) The influence of fluoride in drinking water on the incidence of fluorosis and intelligence of elementary school students in Palu City. GAC SANIT 35:S159–S163. https://doi.org/10.1016/j.gaceta.2021.07.010

  7. Riddell JK, Malin AJ, Flora D, et al (2019) Association of water fluoride and urinary fluoride concentrations with attention deficit hyperactivity disorder in Canadian youth. Environment International 133:105190. https://doi.org/10.1016/j.envint.2019.105190

  8. Liu Y, Téllez-Rojo M, Hu H, et al (2019) Fluoride exposure and pubertal development in children living in Mexico City. Environ Health 18:26. https://doi.org/10.1186/s12940-019-0465-7

  9. Niu R, Xue X, Zhao Y, et al (2015) Effects of fluoride on microtubule ultrastructure and expression of Tub?1a and Tub?2a in mouse hippocampus. Chemosphere 139:422–427. https://doi.org/10.1016/j.chemosphere.2015.07.011

  10. Yuan J, Li Q, Niu R, Wang J (2019) Fluoride exposure decreased learning ability and the expressions of the insulin receptor in male mouse hippocampus and olfactory bulb. Chemosphere 224:71–76. https://doi.org/10.1016/j.chemosphere.2019.02.113

  11. Till C, Green R, Flora D, et al (2020) Fluoride exposure from infant formula and child IQ in a Canadian birth cohort. Environ Int 134:105315. https://doi.org/10.1016/j.envint.2019.105315

  12. Rahman MdM, Bodrud-Doza Md, Siddiqua MostT, et al (2020) Spatiotemporal distribution of fluoride in drinking water and associated probabilistic human health risk appraisal in the coastal region, Bangladesh. Science of The Total Environment 724:138316. https://doi.org/10.1016/j.scitotenv.2020.138316

  13. Kang MJ, Hwang IT, Chung HR (2018) Excessive Iodine Intake and Subclinical Hypothyroidism in Children and Adolescents Aged 6–19 Years: Results of the Sixth Korean National Health and Nutrition Examination Survey, 2013–2015. Thyroid 28:773–779. https://doi.org/10.1089/thy.2017.0507

  14. Bian J, Zhang M, Li F, et al (2022) The Effects of Long-Term High Water Iodine Levels in the External Environment on the Carotid Artery. Biol Trace Elem Res 200:2581–2587. https://doi.org/10.1007/s12011-021-02872-2

  15. Li P, Wu J (2022) Medical Geology and Medical Geochemistry: An Editorial Introduction. Expo Health 14:217–218. https://doi.org/10.1007/s12403-022-00479-z

  16. Liu H-L, Lam LT, Zeng Q, et al (2008) Effects of drinking water with high iodine concentration on the intelligence of children in Tianjin, China. Journal of Public Health 31:32–38. https://doi.org/10.1093/pubmed/fdn097

  17. Carvalho IP, Peixoto B, Caldas JC, et al (2022) Association between Elevated Iodine Intake and IQ among School Children in Portugal. Nutrients 14:4493. https://doi.org/10.3390/nu14214493

  18. Saeed M, Malik RN, Kamal A (2019) Fluorosis and cognitive development among children (6–14 years of age) in the endemic areas of the world: a review and critical analysis. Environ Sci Pollut Res 27:2566–2579. https://doi.org/10.1007/s11356-019-06938-6

  19. Wu J, Wang W, Liu Y, et al (2015) Modifying Role of GSTP1 Polymorphism on the Association between Tea Fluoride Exposure and the Brick-Tea Type Fluorosis. PLOS ONE 10:e0128280. https://doi.org/10.1371/journal.pone.0128280

  20. Carrieri M, Trevisan A, Bartolucci GB (2001) Adjustment to concentration-dilution of spot urine samples: correlation between specific gravity and creatinine. International Archives of Occupational and Environmental Health 74:63–67. https://doi.org/10.1007/s004200000190

  21. Wang H, Liu L, Li S, et al (2007) Determination of iodine ill drinking water by As3+-Ce4?+?catalytic spectrophotometry. Chin J Endemiol 26:333–336

  22. Sun H, Chen W, Wang D, et al (2015) Inverse association between intelligence quotient and urinary retinol binding protein in Chinese school-age children with low blood lead levels: Results from a cross-sectional investigation. Chemosphere 128:155–160. https://doi.org/10.1016/j.chemosphere.2015.01.036

  23. Pérez-Vázquez FJ, Gonz ?alez-Martell FJ, Fern ? andez-Macias JC (2021) Health risk assessment in children living in an urban area with hydrofluorosis: San Luis Potosí Mexico case study. Journal of Trace Elements in Medicine and Biology 7

  24. Bakhurji EA, Alqahtani YS (2018) Fluoride Concentration of Water Supply in Eastern Saudi Arabia: A Preliminary Study. Saudi J Med Med Sci 6:77–81. https://doi.org/10.4103/sjmms.sjmms_176_16

  25. Kassim IAR, Moloney G, Busili A, et al (2014) Iodine Intake in Somalia Is Excessive and Associated with the Source of Household Drinking Water1, 2, 3. The Journal of Nutrition 144:375–381. https://doi.org/10.3945/jn.113.176693

  26. Liu H, Zeng Q, Cui Y, et al (2014) The effects and underlying mechanism of excessive iodide on excessive fluoride-induced thyroid cytotoxicity. Environmental Toxicology and Pharmacology 38:332–340. https://doi.org/10.1016/j.etap.2014.06.008

  27. Liu S, Yu X, Xing Z, et al (2024) The Impact of Exposure to Iodine and Fluorine in Drinking Water on Thyroid Health and Intelligence in School-Age Children: A Cross-Sectional Investigation. Nutrients 16:2913. https://doi.org/10.3390/nu16172913

  28. Yu G, Sun D (2003) The significance of urinary fluoride content on the endemic fluorsis. Chinese Journal of Endemiology 80–82

  29. Ding Y, YanhuiGao, Sun H, et al (2011) The relationships between low levels of urine fluoride on children’s intelligence, dental fluorosis in endemic fluorosis areas in Hulunbuir, Inner Mongolia, China. Journal of Hazardous Materials 186:1942–1946. https://doi.org/10.1016/j.jhazmat.2010.12.097

  30. Jin T, Huang T, Zhang T, et al (2024) A Bayesian benchmark concentration analysis for urinary fluoride and intelligence in adults in Guizhou, China. Science of The Total Environment 925:171326. https://doi.org/10.1016/j.scitotenv.2024.171326

  31. Zimmermann MB, Aeberli I, Andersson M, et al (2013) Thyroglobulin is a sensitive measure of both deficient and excess iodine intakes in children and indicates no adverse effects on thyroid function in the UIC range of 100–299 ?g/L: a UNICEF/ICCIDD study group report. J Clin Endocrinol Metab 98:1271–1280. https://doi.org/10.1210/jc.2012-3952

  32. Veneri F, Vinceti M, Generali L, et al (2023) Fluoride exposure and cognitive neurodevelopment: Systematic review and dose-response meta-analysis. Environmental Research 221:115239. https://doi.org/10.1016/j.envres.2023.115239

  33. World Health Organization (2007) Assessment of iodine deficiency disorders and monitoring their elimination: a guide for programme managers. 1

  34. Ren S, Zhong Z (2014) Meta-analysis on the relationship between Chinese children’s intelligence and excessive iodine. Jounalofhygieneeseach 43:133–138. https://www.doi.org/DOI:10.19813/j.cnki.weishengyanjiu.2014.01.035

  35. Cui Y, Yu J, Zhang B, et al (2020) The relationships between thyroid-stimulating hormone and/or dopamine levels in peripheral blood and IQ in children with different urinary iodine concentrations. Neuroscience Letters 729:134981. https://doi.org/10.1016/j.neulet.2020.134981

  36. Jiang Y, Guo X, Sun Q, et al (2016) Effects of Excess Fluoride and Iodide on Thyroid Function and Morphology. Biol Trace Elem Res 170:382–389. https://doi.org/10.1007/s12011-015-0479-0

  37. Griebel-Thompson AK, Sands S, Chollet-Hinton L, et al (2023) A Scoping Review of Iodine and Fluoride in Pregnancy in Relation to Maternal Thyroid Function and Offspring Neurodevelopment. Advances in Nutrition 14:317–338. https://doi.org/10.1016/j.advnut.2023.01.003

  38. Meng Z, Liu M, Zhang Q, et al (2015) Gender and Age Impacts on the Association Between Thyroid Function and Metabolic Syndrome in Chinese. Medicine 94:e2193. https://doi.org/10.1097/MD.0000000000002193

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Acknowledgements

The project was funded by the Jiangsu Province Association of Endemic Diseases Scientific Research Project on Schistosomiasis, Parasitic Diseases, and Endemic Diseases (Grant No. x201824, x202119, x202325). We thank the staff of the Xuzhou, Fengxian, and Peixian CDCs for their support in the epidemiological investigation and laboratory work. We extend our gratitude to the schools and students who participated in this study.

Author information

Authors and Affiliations

  1. Department of Environment and Health (Endemic Disease Control and Prevention), Jiangsu Provincial Center for Disease Control and Prevention, 172 Jiangsu Road, Nanjing, 210009, Jiangsu, China

    Yuting Xia, Yunjie Ye, Mao Liu, Yang Wang, Li Shang, Peihua Wang & Hong Sun

Corresponding author

Correspondence to Hong Sun.