Relationship between excess iodine, thyroid function, blood pressure, and blood glucose level in adults, pregnant women, and lactating women: A cross-sectional study.

High water iodine concentration in drinking water can lead to excessive iodine, which will affect normal thyroid function, blood glucose, and blood pressure, especially among pregnant and lactating women. The aim of the present study was to determine the relationship between iodine, thyroid function, blood pressure, and blood glucose level among adults, and pregnant and lactating women in areas that are iodine-adequate (IA) and iodine-excess (IE) with respect to iodine concentrations in drinking water. A cross-sectional survey was conducted involving 144 pregnant and 237 lactating women in Shanxi Province, and 828 adults in Shandong Province. Water iodine, urinary iodine, thyroid function, blood pressure, and blood glucose were measured. Compared with the IA area, the water iodine concentration (WIC) in the IE area was higher (adults, 325.00 µg/L vs. 71.40 µg/L; pregnant and lactating women, 464.80 µg/L vs. 57.50 µg/L). For adults, and pregnant and lactating women, in the IE area, the urinary iodine concentration (UIC), free thyroxine (FT4 [except for lactating women]), and systolic blood pressure (only adults 18-40 years of age) were significantly higher, while the blood glucose level and the prevalence of hyperglycemia (except for adults) was lower, and the free triiodothyronine (FT3), thyroid-stimulating hormone (TSH), thyroglobulin antibody (TgAb), thyroid peroxidase antibody (TPOAb), and hypertension-positive rates of the three populations were not significantly different. For adults, systolic and diastolic pressure were positively correlated with FT3 and FT4, respectively, while the blood glucose level were inversely associated with the WIC. For pregnant women, systolic pressure and the WIC, diastolic pressure and FT4, blood glucose level and FT3 were all positively correlated, while the blood glucose level was inversely associated with TSH, WIC and UIC. For lactating women, systolic pressure was positively correlated with WIC and UIC, while blood glucose level were inversely associated with WIC and UIC. Pregnant and lactating women in the IE area were at lower risk for an association with hyperglycemia. Collectively, our research showed that long-term exposure to high water iodine is a high-risk factor for abnormal blood pressure and a low-risk factor for abnormal blood glucose level, especially for special populations such as pregnant and lactating women. Moreover, enhanced monitoring of blood pressure and blood glucose level in people with abnormal thyroid function in areas with high water iodine is important.