Abstract
ObjectivesPerchlorate, nitrate, and thiocyanate are well-known inhibitors of the sodium-iodide symporter and may disrupt thyroid function. This exploratory study investigated the association among urinary perchlorate, nitrate, and thiocyanate concentrations and parathyroid hormone (PTH) levels in the general U.S. population.MethodsWe analyzed data on 4265 adults (aged 20 years and older) from the National Health and Nutrition Examination Survey in 2005 through 2006 to evaluate the relationship among urinary perchlorate, nitrate, and thiocyanate concentration and PTH levels and the presence of hyperparathyroidism cross-sectionally.ResultsThe geometric means and 95% confidence interval (95% CI) concentrations of urinary perchlorate, nitrate, and thiocyanate were 3.38 (3.15–3.62), 40363 (37512–43431), and 1129 (1029–1239) ng/mL, respectively. After adjusting for confounding variables and sample weights, creatinine-corrected urinary perchlorate was negatively associated with serum PTH levels in women (P = 0.001), and creatinine-corrected urinary nitrate and thiocyanate were negatively associated with serum PTH levels in both sex groups (P = 0.001 and P<0.001 for men, P = 0.018 and P<0.001 for women, respectively). Similar results were obtained from sensitivity analyses performed for exposure variables unadjusted for creatinine with urinary creatinine added as a separate covariate. There was a negative relationship between hyperparathyroidism and urinary nitrate and thiocyanate [odds ratio (95% CI) = 0.77 (0.60–0.98) and 0.69 (0.61–0.79), respectively].ConclusionsA higher urinary concentration of perchlorate, nitrate, and thiocyanate is associated with lower serum PTH levels. Future studies are needed to determine the pathophysiological background of the observation.
Highlights
Monovalent anions such as perchlorate, nitrate, fluoroborate, and thiocyanate are known to competitively inhibit iodide uptake and may disrupt thyroid function [1, 2]
A higher urinary concentration of perchlorate, nitrate, and thiocyanate is associated with lower serum parathyroid hormone (PTH) levels
A study showed that higher nitrate levels in public water supplies were associated with an increased risk of thyroid cancer, and higher intake of dietary nitrate was associated with an increased risk of thyroid cancer and hypothyroidism [7]
Summary
Monovalent anions such as perchlorate, nitrate, fluoroborate, and thiocyanate are known to competitively inhibit iodide uptake and may disrupt thyroid function [1, 2]. For U.S adults, vegetables and dairy products are major contributor of perchlorate in the diet [5]. The majority of nitrate intake comes from drinking water and food [6]. Thiocyanate enters the body from the diet (such as cruciferous vegetables) or is synthesized from cyanide by sulfur transferase enzymes. Smoking cigarettes is the major sources of cyanide exposure for those who do not work in cyanide-related industries. Thiocyanate level can be used as an indicator for tobacco smoke exposure, but there is a large overlap between smokers and nonsmokers because of numerous other sources for cyanide [8]. Risk assessment for perchlorate exposure should consider co-exposure to nitrate and thiocyanate [9]
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