Low urinary selenium levels are associated with iodine deficiency in Brazilian schoolchildren and adolescents

Background Selenium (Se) and iodine (Io) are important micronutrients for the proper functioning of the thyroid gland, as they are crucial for the synthesis and activation of the thyroid hormones (TH) triiodothyronine (T 3 ) and thyroxine (T 4 ). Objective To evaluate the Se and Io nutritional status among schoolchildren. Methodology Cross-sectional, descriptive and analytical study conducted in 982 schoolchildren aged 6–14 years from public schools in the state of Bahia, Brazil. Sociodemographic and anthropometric variables, as well as urinary Se (USC) and Io concentrations (UIC) using the inductively coupled plasma mass spectrometry (ICP-MS) method and thyroid-stimulating hormone (TSH) from filter paper blood collection, were evaluated. Results The median USC and UIC were 38.7 and 210.0 (IQR: 26.8–52.9 and 129.3–334.1 μg/L, respectively). The prevalence of iodine deficiency and excessive UIC were observed in 17.1% and 30.9% of schoolchildren, respectively. Concomitant low USC and IoD was found in 3.9% of schoolchildren. There was a positive correlation between USC and UIC ( r = 0.60; p = 0.00). The median TSH was 0.95 (IQR: 0.69–1.30 µUI/L). Conclusions This study demonstrates that USC is a good biomarker for assessing Se status, meantime more studies are needed to establish cutoff USC in child population. Despite adequate median intake, a subgroup of schoolchildren had IoD and low USC. The correlation between UIC and USC point at the importance of two micronutrients, raising the question whether measuring Se should be included in monitoring programs that address the prevention of nutritional disturbances.