Carolina Gutiérrez-Repiso1, Natalia Colomo1, Gemma Rojo-Martinez2, Sergio Valdés2, Maria J Tapia3, Isabel Esteva2, Maria S Ruiz de Adana2, Elehazara Rubio-Martin1, Ana Lago-Sampedro1, Piedad Santiago4, Ines Velasco5, Eduardo Garcia-Fuentes6, Jose C Moreno7, Federico Soriguer2. 1. Unidad de Gestión Clínica de Endocrinología y Nutrición, Instituto de Investigaciones Biomédicas de Málaga (IBIMA), Hospital Regional Universitario, Málaga, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Instituto de Salud Carlos IIII, Málaga, Spain. 2. Unidad de Gestión Clínica de Endocrinología y Nutrición, Instituto de Investigaciones Biomédicas de Málaga (IBIMA), Hospital Regional Universitario, Málaga, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Instituto de Salud Carlos IIII, Málaga, Spain; CIBER de Fisiopatología Obesidad y Nutrición (CIBEROBN), Instituto de Salud Carlos III, Málaga, Spain. 3. Unidad de Gestión Clínica de Endocrinología y Nutrición, Instituto de Investigaciones Biomédicas de Málaga (IBIMA), Hospital Regional Universitario, Málaga, Spain. 4. Endocrinology and Nutrition Department, Complejo Hospitalario de Jaén, Jaén, Spain. 5. Unidad de Gestión Clínica Materno-Infantil, Hospital de Riotinto, Huelva, Spain. 6. Unidad de Gestión Clínica de Endocrinología y Nutrición, Instituto de Investigaciones Biomédicas de Málaga (IBIMA), Hospital Regional Universitario, Málaga, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Instituto de Salud Carlos IIII, Málaga, Spain. Electronic address: edugf1@gmail.com. 7. Molecular Thyroid Laboratory, INGEMM-Institute for Medical and Molecular Genetics, La Paz University Hospital, Madrid, Spain.
Abstract
BACKGROUND & AIMS: Few prospective cohort studies have evaluated dietary iodine intake and urinary iodine concentrations in the general adult population. We assess the evolution of urinary iodine excretion and factors that may influence it in an adult population followed for 11 years. METHODS: A population-based cohort study was undertaken in Pizarra (Spain). In the three study phases (baseline (n = 886), and 6 (n = 788) and 11 years later (n = 501)), participants underwent an interview and a standardized clinical examination that included a food questionnaire, and thyroid hormone and urinary iodine determinations. Subjects with thyroid dysfunction, palpable goiter or urinary iodine excretion >400 μg/L were excluded. RESULTS: Urinary iodine increased over the years (100.6 ± 70.0 μg/L at baseline vs. 125.4 ± 95.2 μg/L at 6 years and 141.6 ± 81.4 μg/L at 11 years; p < 0.0001). Urinary iodine was significantly higher in subjects who reported iodized salt consumption and in subjects with a higher intake of dairy products (p < 0.05). Consumption of iodized salt (Risk ratio (RR) = 1.23, 95% CI [1.01-2.05]) and dairy products (RR = 2.07, 95% CI [1.01-4.23]), and a baseline urinary iodine concentration ≥100 μg/L (RR = 1.26, 95% CI [1.04-1.53]) were significantly associated with urinary iodine concentrations ≥100 μg/L at 11 years. There is no correlation between thyroid function (TSH, free triiodothyronine or free thyroxine levels) and urinary iodine concentrations in conditions of iodine sufficiency. CONCLUSIONS: The increase in urinary iodine concentrations over eleven years is associated with an increase in iodized salt intake and with the dairy products intake, and possibly with a higher iodine content of dairy products. However, individual variability in urinary iodine excretion was not fully explained by dietary iodine intake alone; previous urinary iodine concentrations were also important.
BACKGROUND & AIMS: Few prospective cohort studies have evaluated dietary iodine intake and urinary iodine concentrations in the general adult population. We assess the evolution of urinary iodine excretion and factors that may influence it in an adult population followed for 11 years. METHODS: A population-based cohort study was undertaken in Pizarra (Spain). In the three study phases (baseline (n = 886), and 6 (n = 788) and 11 years later (n = 501)), participants underwent an interview and a standardized clinical examination that included a food questionnaire, and thyroid hormone and urinary iodine determinations. Subjects with thyroid dysfunction, palpable goiter or urinary iodine excretion >400 μg/L were excluded. RESULTS: Urinary iodine increased over the years (100.6 ± 70.0 μg/L at baseline vs. 125.4 ± 95.2 μg/L at 6 years and 141.6 ± 81.4 μg/L at 11 years; p < 0.0001). Urinary iodine was significantly higher in subjects who reported iodized salt consumption and in subjects with a higher intake of dairy products (p < 0.05). Consumption of iodized salt (Risk ratio (RR) = 1.23, 95% CI [1.01-2.05]) and dairy products (RR = 2.07, 95% CI [1.01-4.23]), and a baseline urinary iodine concentration ≥100 μg/L (RR = 1.26, 95% CI [1.04-1.53]) were significantly associated with urinary iodine concentrations ≥100 μg/L at 11 years. There is no correlation between thyroid function (TSH, free triiodothyronine or free thyroxine levels) and urinary iodine concentrations in conditions of iodine sufficiency. CONCLUSIONS: The increase in urinary iodine concentrations over eleven years is associated with an increase in iodized salt intake and with the dairy products intake, and possibly with a higher iodine content of dairy products. However, individual variability in urinary iodine excretion was not fully explained by dietary iodine intake alone; previous urinary iodine concentrations were also important.