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.

The present study aimed to evaluate the status of iodine nutrition and thyroid function in adults, to understand the distribution of thyroid disease in people with autoimmune thyroid disease (AITD) in different water iodine areas and to explore the relationship between serum iodine, urine iodine and thyroid function in people with AITD. A cross-sectional survey was conducted in areas of Shandong Province with different water iodine levels, and subsequently 1225 adults were enrolled from iodine-deficient (ID), iodine-adequate (IA) and iodine-excess (IE) areas. Urinary iodine, water iodine, salt iodine, serum iodine and thyroid function were measured. According to the urine iodine concentration, the ID and IA areas were defined as iodine sufficient and the IE area as iodine excessive. Urine iodine, serum iodine, free thyroxine (FT₄) and thyroid-stimulating hormone (TSH) levels were comparatively higher in the IE area. The positive rate of thyroglobulin antibody (19·1 %) and the prevalence of AITD (21·8 %) were higher in the ID areas; the prevalence of subclinical hypothyroidism was lowest in the ID areas (7·3 %) and highest in the IE area (16·3 %). Among the AITD population, urinary iodine concentration, free triiodothyronine, FT₄ and TSH had a non-linear correlation with serum iodine; abnormal TSH level, serum iodine concentration > 110 µg/l and goitre were risk factors for AITD in adults, especially females. Our data collectively suggest that universal salt iodisation has improved the iodine nutritional status of the population in ID areas in China. Non-step-by-step iodine fortification may induce the transformation of thyroid autoimmune diseases from recessive-to-dominant in susceptible people. Moreover, enhanced monitoring of thyroid function in people with AITD is important.

Iodine is important in both thyroid function and lipid metabolism. Some studies have explored the effect of thyroid hormones (THs) and urinary iodine concentration (UIC) on serum lipid levels. However, the association between iodine intake and dyslipidemia has not been well established. This study aimed to investigate the relationship between water iodine concentration (WIC) and dyslipidemia, including hypercholesterolemia, hypertriglyceridemia, low high-density lipoprotein cholesterol (HDL-C) and high low-density lipoprotein cholesterol (LDL-C). A cross-sectional survey was conducted involving 409, 390 and 436 adults (≥18 years) from the iodine-deficient (median water iodine, MWI < 10 µg/L), iodine-adequate (MWI between 40 and 100 µg/L) and iodine-excess (MWI > 100 µg/L) areas, respectively. WIC, total cholesterol (TC), triglyceride (TRIG), HDL-C and LDL-C were measured. The prevalence of dyslipidemia were calculated based on the level of WIC using the chi-square method. To further explore whether prevalence was associated with WIC, simple linear regressions and multiple logistic regression models were used. Compared to those with WIC of 40-100 µg/L, a WIC of >100 µg/L was found to be protective associated with against the occurrence of hypertriglyceridemia [adjusted odds ratio (AOR) = 0.649, 95% confidence interval (CI): 0.455-0.924] and low HDL-C (AOR = 0.429, 95% CI: 0.264-0.697). The prevalence of hypertriglyceridemia, low HDL-C and high LDL-C as a function of WIC was found to be an inverted U-shaped association with a zenith at a WIC of 40-100 µg/L. Collectively, our research showed that serum lipid levels are related to WIC. The benefit effect association between WIC and dyslipidemia appears in cases of iodine excess (>100 µg/L).