Impact of lead exposure on the thyroid glands of individuals living in high- or low-lead exposure areas

Abstract

Ecuador was an endemic area for iodine deficiency; however, due to the population consumption of iodized table salt, the country is nowadays considered iodine sufficient. Despite the population consumption of iodized salt for more than 50 years, the prevalence of hypothyroidism has increased in recent years. A similar increment has been reported for thyroid cancer (TC) becoming the second most common cancer in women and seventh most common cancer in men. High blood lead (BPb) level is a controversial causal factor for impaired thyroid function as well as a debated environmental cause for the increased incidence of TC. To study the association between BPb and thyroid function, anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin (anti-Tg) antibodies, and the presence of benign and malignant thyroid nodules in Ecuadorian individuals living in high lead exposure (HE) areas compared with those living in low lead exposure (LE) area. We evaluated 197 euthyroid individuals: 70 from Esmeraldas (close to a petrol refinery) and 27 from La Victoria de Pujilí (Pb-glazing ceramics), considered HE areas, and 100 from Quito, considered the LE area. In parallel, we evaluated 187 patients with hypothyroidism (60, 27, and 100 patients from Esmeraldas, Pujilí, and Quito, respectively). BPb was detected using atomic absorption spectroscopy, while thyroid-stimulating hormone (TSH), free-thyroxine (FT4), and autoantibodies were measured using chemiluminescence assays. Thyroid ultrasonography was performed in 300 individuals and fine-needle aspiration biopsy (FNA) was performed only when required based on the guidelines of the American Thyroid Association. The BPb levels (mean ± SD) in the HE areas were increased (8.5 ± 7.4) than those in the LE area (3.2 ± 2.4, P < .001). No significant associations were observed between BPb and TSH, FT4, or thyroid antibody levels. Enlarged thyroid glands and larger thyroid nodules were primarily observed in HE areas. Just 1 TC was observed. High BPb levels detected in HE areas were not associated with thyroid function or thyroid autoantibodies; however, increased thyroid size and numbers of thyroid nodules were observed, demanding further actions to control lead contamination in these Ecuadorian areas.