  Citation: García-Torres, E.; Pérez-Morales, R.; González-Zamora, A.; Calleros-Rincón, E.Y. Subclinical Hypothyroidism in Families Due to Chronic Consumption of Nitrate-Contaminated Water in Rural Areas with Intensive Livestock and Agricultural Practices in Durango, Mexico. Water 2022, 14, 282. https://doi.org/10.3390/w14030282 Academic Editor: Alessandra Marzadri Received: 1 December 2021 Accepted: 12 January 2022 Published: 18 January 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). water Article Subclinical Hypothyroidism in Families Due to Chronic Consumption of Nitrate-Contaminated Water in Rural Areas with Intensive Livestock and Agricultural Practices in Durango, Mexico Edgar García-Torres 1 , Rebeca Pérez-Morales 2 , Alberto González-Zamora 3 and Esperanza Yasmín Calleros-Rincón 1, * 1 Faculty of Chemical Sciences, Juarez University of the State of Durango, Av. Artículo 123 s/n. Fracc. Filadelfia, Gomez Palacio 35010, Mexico; edgar.garcia@ujed.mx 2 Cellular and Molecular Biology Laboratory, Faculty of Chemical Sciences, Juarez University of the State of Durango, Av. Artículo 123 s/n. Fracc. Filadelfia, Gomez Palacio 35010, Mexico; rebecapms@ujed.mx 3 Evolutionary Biology Laboratory, Faculty of Biological Sciences, Juarez University of the State of Durango, Av. Universidad s/n. Fracc. Filadelfia, Gomez Palacio 35010, Mexico; agzfc@ujed.mx * Correspondence: dra.ecallerosrincon@ujed.mx; Tel.: +52-871-715-88-10 Abstract: Nitrate is a widely disseminated water pollutant and has been linked to health disorders, including hypothyroidism. Here, we evaluated the relationship between thyroid function and chronic exposure to nitrates in rural zone families, in addition to the genetic and autoimmune factors. Expo- sure and effect biomarkers, thyroid hormones, and autoantibodies of tiroperoxidase were measured, as well the presence of two FOXE1 polymorphisms (rs965513, rs1867277). Pearson’s correlation, principal component analysis, Kruskal–Wallis, and chi-squared tests were used for statistical analysis. A total of 102 individuals were analyzed; 45% presented subclinical hypothyroidism, a negative correlation was observed between methemoglobin and the total T3 (r = -0.43, p = 0.001) and free T3 levels (r = -0.34, p = 0.001), as well as between TSH and the free T4 (r = -0.41, p = 0.0001) and total T4 (r = -0.36, p = 0.0001). A total of 15.7% had positive antithyroid ab-TPO, while the polymorphic genotype (AA) represented only 3% (rs965513) and 4% (rs1867277) among subjects with subclinical hypothyroidism. The high frequency of subclinical hypothyroidism in the population under study could be related, mainly, to chronic exposure through the consumption of nitrate-contaminated water. Keywords: subclinical hypothyroidism; nitrates; chronic exposure; contaminated water 1. Introduction Groundwater is the main source of drinking water, as well as a stable and reliable resource that meets the demand for human consumption [1]. Access to water is important to sustain the basic activities of all living beings and is closely related to the development of urban and rural areas. [2]. However, in recent years, the contamination of these has been conditioned by the increase in the levels of nitrogen compounds, specifically nitrate, as a result of leaching, mainly due to anthropogenic activities such as the use of soils for intensive agriculture [3], intensive livestock farming [4], the use of nitrogenated chemical fertilizers [5], the use of animal manure as an organic fertilizer, the production and disposal of urban wastewater [6], the disposal of septic waste and effluents from septic tanks or leaks that also contribute to pollution in settlement environments [7,8]. The latter, in conjunction with geological features [9], rainfall fluctuations [10], interactions with surface water [11], changes in water tables [12], and the presence of biological processes such as denitrification [13], can promote the variation of nitrate concentrations, thus exceeding Water 2022, 14, 282. https://doi.org/10.3390/w14030282 https://www.mdpi.com/journal/water