Effect of dietary iodine on thyroid hormones and energy blood metabolites in lactating goats

Association of urinary iodine concentration with prediabetes/diabetes in adults: Analysis of the NHANES 2005-2016

BACKGROUND & AIMS

Iodine is required for synthesizing thyroid hormones and regulating human metabolism. Iodine deficiency can lead to thyroid function abnormalities, which are closely associated with disturbances in glucose-insulin homeostasis. Research on the relationship between iodine and diabetes/prediabetes in adults was sparse and inconsistent. We assessed trends in urinary iodine concentration (UIC) and diabetes/prediabetes prevalence and focused on the association between iodine and diabetes/prediabetes among U.S. adults.

METHODS

We analyzed the National Health and Nutrition Examination Survey (NHANES) data from the 2005-2016 cycles. Linear regression was employed to evaluate UIC and prediabetes/diabetes prevalence trends over time. Both multiple logistic regression and restricted cubic splines (RCS) were performed to evaluate the association of UIC with diabetes/prediabetes.

RESULTS

A distinctly declining trend in median UIC and a significant increase in diabetes prevalence in U.S. adults from 2005 to 2016 were observed. The fourth quartile of UIC was associated with a 30% lower risk for prediabetes, compared with the first quartile (OR=0.70, 95% CI: 0.56-0.86, P_trend=0.001). However, UIC was not significantly associated with the prevalence of diabetes. The RCS model suggested a significant nonlinear relationship between UIC and the risk of diabetes (P for nonlinearity =0.0147). Stratification analysis showed that the negative associations of UIC with the risk of prediabetes were more pronounced in participants who were men, aged 46-65, overweight, light alcohol drinkers, and nonactive smokers.

CONCLUSIONS

Overall, the adults' median UIC in the U.S. population was a declining trend. However, diabetes prevalence increased significantly from 2005 to 2016. Higher UIC was associated with a lower risk of prediabetes.

Impact of urinary iodine concentration on blood glucose levels and blood pressure: a nationwide population-based study

PURPOSE

Iodine is a vital trace element for systemic metabolic control as well as thyroid hormone synthesis. Though iodine has significant antioxidant and anti-inflammatory effects, reports on its effects on metabolic disorders are limited and inconsistent.

METHODS

Impact of urinary iodine concentrations (UICs) on fasting blood glucose (FBG) levels and blood pressure (BP) in the general Korean population was evaluated adjusting for covariates including thyrotropin level and presence of thyroid diseases.

RESULTS

The median UIC was 302.3 μg/L in all participants and was significantly lower in those with dysglycemia (303.6 μg/L in normal participants, 285.1 μg/L in participants with FBG levels of 100-125 mg/dL, and 261.8 μg/L in participants with FBG levels ≥ 126 mg/dL; p = 0.002). Similarly, the UIC was lower in participants with higher BP (311.6 μg/L in normal participants, 288.7 μg/L in prehypertensive participants, and 265.8 μg/L in hypertensive participants; p < 0.001). The multiple linear regression model showed a negative correlation between the UIC and FBG levels (p = 0.002), and the UIC and systolic BP (p < 0.001). One standard deviation increase in the UIC showed odds ratios of 0.84 (95% confidence interval [CI] = 0.73-0.98) for elevated FBG levels (≥ 100 mg/dL) and 0.94 (95% CI = 0.88-0.99) for elevated SBP (≥ 120 mm Hg) after full adjustment.

CONCLUSION

Higher UICs were associated with lower FBG and BP levels, independent of thyroid function and other confounding factors in Korea, an iodine-replete country.

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.

Iodine nutrition status and its association with microvascular complications in urban dwellers with type 2 diabetes

Background

The principal function of iodine acts on thyroid function, but in recent years, the role of iodine deficiency in metabolism has also been gradually revealed. We aimed to investigate the current status of iodized salt consumption and urinary iodine concentration (UIC) in an urban Chinese population with type 2 diabetes, and to further explore whether UIC was associated with diabetic microvascular complications.

Methods

Four thousand five hundred fifty-nine subjects with diabetes from 7 communities in downtown Shanghai were enrolled in the cross-sectional Metal Study in 2018. UIC was detected using an inductively coupled plasma-mass spectrometer. Diabetic kidney disease (DKD) was defined as urinary albumin-to-creatinine ratio (UACR) > 30 mg/g or estimated glomerular filtration rate < 60 mL/min/1.73 m². Diabetic retinopathy (DR) was evaluated by high-quality fundus photographs and was remotely read by ophthalmologist.

Results

The median UIC of subjects with diabetes was 115.4 μg/L (78.9–170.8) in downtown Shanghai. Among all the subjects, 52.7% consumed non-iodized salt and 40.4% were iodine deficient. Iodine deficiency (UIC < 100 μg/L) was associated with an increased odds of DKD (OR 1.17; 95%CI 1.01–1.37) after adjustment for age, sex, education, current smokers, BMI, HbA1c, duration of diabetes, dyslipidemia, thyroid-stimulating hormone and free thyroxine. No association was observed between UIC and DR after multivariable adjustment.

Conclusions

A concerning number of subjects with diabetes consumed non-iodized salt and suffered from iodine deficiency in coastal regions of China. Low UIC might be a risk factor for DKD, which should be further confirmed by longitudinal prospective studies.

U-Shaped Associations Between Urinary Iodine Concentration and the Prevalence of Metabolic Disorders: A Cross-Sectional Study

Background: Iodine is important in both thyroid function and human metabolism. Studies have explored the effect of iodine on metabolic disorders through thyroid function. This study aimed to investigate the relationship between iodine status and metabolic disorders, such as metabolic syndrome (MetS), hypertension, impaired glucose metabolism, central obesity, and dyslipidemia. Methods: A total of 51,795 subjects aged ≥18 years from the TIDE (Thyroid Disorders, Iodine Status and Diabetes, a national epidemiological cross-sectional study) program were included. The prevalence of metabolic disorders and its related diseases was calculated based on the level of urinary iodine concentrations (UICs) using the chi-square method. To further explore whether the prevalence was associated with UIC, quadratic and UIC-stratified logistic regression models were used. Results: The prevalence of metabolic disorders as a function of UIC was found to be U-shaped with a lower prevalence of 76.0% at an UIC of 300-499 μg/L. Participants with an UIC of 300-499 μg/L showed an association with metabolic disorders (odds ratio [OR] = 0.857, 95% confidence interval [CI 0.796-0.922]) and hypertension (OR = 0.873 [CI 0.814-0.936]). An UIC of 300-799 μg/L was found to be associated with the occurrence of MetS and impaired glucose tolerance. An UIC of 500-799 μg/L was associated with the occurrence of prediabetes (OR = 0.883 [CI 0.797-0.978]). An UIC of ≥300 μg/L was associated with the occurrence of hypertriglyceridemia, hypercholesterolemia, and high levels of low-density lipoprotein cholesterol. Furthermore, an UIC of <100 μg/L showed an association with hypertension (OR = 1.097 [CI 1.035-1.162]) and hypercholesterolemia (OR = 1.178 [CI 1.117-1.242]). Conclusions: The association between UICs in adults and metabolic disorders and its related diseases is U-shaped. The association between UIC and metabolic disorders disappears in cases of iodine deficiency (<100 μg/L) or excess (≥500 μg/L).

The impact of dietary supplementation with guava (Psidium guajava L.) agroindustrial waste on growth performance and meat quality of lambs

The aim of this study was to evaluate the growth performance and meat quality of lambs (40 animals) fed with increasing levels (0; 7.5; 15.0; 22.5 and 30.0%) of guava agroindustrial waste (GAW). The pH, cooking loss, colour and chemical composition were measured in the Longissimus lumborum (LL) muscle. A sensory analysis was performed with a panel of eight trained testers using a quantitative descriptive method in order to define sensory descriptors and their intensities. The lambs obtained a mean weight gain of 316 g/day consuming 1.32 kg/day of dry matter. The inclusion of GAW in the diet of lambs did not affect pH, L*, a* and b*. However, significant difference (P < .05) among the treatments were obtained for the chemical composition of LL: moisture decreased, while ash increased and intramuscular fat increased until 15% and then decreased at 22.5% with the inclusion of GAW. However, the sensorial characteristics of lamb meat (lamb odour and flavour, tenderness and juiciness) were not affect by the inclusion of GAW. Therefore, GAW can be included up to 30% in lamb feed without compromising the performance, physic-chemical and sensory characteristics of meat.

Effects of Excessive Iodine Intake on Blood Glucose, Blood Pressure, and Blood Lipids in Adults

To understand the effects of excess iodine intake on blood glucose, blood pressure, and blood lipids in adults. We selected three villages from Shanxi Province to conduct cross-sectional survey: Maxi [median water iodine concentration (MWIC) 6.3 μg/L, median urinary iodine concentration (MUIC) 126.6 μg/L, 320 adults]; Xiwenzhuang (MWIC 79.8 μg/L, MUIC 221.2 μg/L, 264 adults); and Gaoche (MWIC 506.0 μg/L, MUIC 421.3 μg/L, 241 adults). According to the urinary iodine levels in adults, the three villages were defined as iodine-adequate, iodine-sufficient, and iodine-excess. Urinary iodine, water iodine, thyroid function, blood glucose, blood pressure, and blood lipids were measured. Compared with the iodine-adequate area, blood glucose and systolic and diastolic pressure of adults in iodine-sufficient and iodine-excess areas increased and high-density lipoprotein-cholesterol decreased (all P < 0.001). Urinary iodine, thyroid-stimulating hormone, and free thyroxine have a nonlinear correlation with blood glucose (R² = 0.8174, 0.8264, and 0.8520, respectively). Excessive iodine intake may result in elevated blood glucose and blood pressure and has some influence on blood lipids, and may increase the risk of hypertension and diabetes.

Dietary Iodine Affected the GSH-Px to Regulate the Thyroid Hormones in Thyroid Gland of Rex Rabbits

Iodine (I) is an essential trace element that can influence animal health and productivity. In this study, we investigated the effects of dietary iodine on the antioxidant indices of organ (liver and thyroid gland) and messenger RNA (mRNA) expression of glutathione peroxidase (GSH-Px) in Rex rabbits. A total of 120 4-month-old Rex rabbits (2235.4 ± 13.04 g BW) were divided into four equal groups, and their diets were supplemented with iodine (0, 0.2, 2, or 4 mg/kg dry matter (DM)). The iodine concentration in basal diet (control group) was 0.36 mg/kg DM. In most of measured parameters, supplemental iodine exerted no significant effect. Growth and slaughter performance and organ weight were not influenced significantly by iodine supplementation. Serum T₃ was significantly lower in 2-mg I group than in 0.2 and 4-mg I groups (P < 0.05). Superoxide dismutase (SOD), GSH-Px, methane dicarboxylic aldehyde (MDA), and thyroperoxidase (TPO) in the serum and liver were not influenced (P > 0.05). Conversely, serum catalase (CAT) was significantly reduced (P < 0.05). In the thyroid, GSH-Px was higher in the 2-mg I group than in the 0.2- and 4-mg I groups (P < 0.05). RT-PCR results showed that the mRNA expression level of GSH-Px in the liver was not significantly influenced (P > 0.05). In the thyroid gland, the mRNA expression level of GSH-Px was higher in the 2-mg I group than in the 4-mg I group (P < 0.05), which agreed with the activity of GSH-Px. In conclusion, iodine supplementation exerted no effect on the performance and antioxidant capacity of the body, but dietary iodine influenced serum T₃ or GSH-Px in the thyroid gland. Thus, on the basis of serum T₃ and GSH-Px levels in the thyroid gland, we hypothesized that GSH-Px secretion was increased by adding dietary iodine in the thyroid, which may inhibit the H₂O₂ generation and further influence the thyroid hormone synthesis.