Correlation between iodine intake and thyroid function in subjects with normal thyroid function

Effects of maternal iodine nutritional status on neurodevelopmental and cognitive function of rat offspring

Objectives

This study aimed to explore the effect of maternal iodine status on the brain development of offspring in rats. Since in human studies, the interference of environmental factors and other nutrients cannot be removed.

Materials and methods

A total of 48 female Wistar rats were randomly divided into four groups: low iodine (LI), normal iodine (NI), 10-fold high iodine (10HI), and 50-fold high iodine (50HI). The rats were killed on the 15th day of pregnancy and lactation after collecting 24-h urine. The iodine concentration in 24-h urine, blood, and placenta of pregnant rats, and 24-h urine, milk, blood, and mammary glands of lactating rats was determined by inductively coupled plasma mass spectrometry. The thyroid hormone of pregnant and lactating rats was detected by chemiluminescence. The offspring were subjected to the Morris water maze on the 10th day after birth. Serum was collected to detect the thyroid hormone of offspring. The protein expression of neuroendocrine-specific protein (NSP)-A and brain-derived neurotrophic factor (BDNF) in the offspring brain were studied.

Results

Iodine storage in the placenta during pregnancy and mammary glands during lactation was positively correlated with iodine intake, and iodine storage in the placenta and mammary glands in the 50HI group was significantly higher than that in the NI group (P = 0.045 and P = 0.040). Compared with the NI group, the offspring thyroid-stimulating hormone (TSH) level was significantly higher in the 10HI group (P = 0.046), and the FT4 level was significantly lower in the 50HI group (P = 0.032). The Morris water maze showed that LI and 50HI groups required longer time and distance to find the platform than the NI group (P < 0.001). The platform crossing numbers in the LI and 50HI groups decreased significantly (P < 0.001). The expression of NSP-A in offspring brain was lower in the 10HI and 50HI groups than in the NI group (P = 0.026 and P = 0,008). BDNF expression levels were significantly lower in the LI, 10HI, and 50HI groups than in the NI group (P < 0.001).

Conclusion

Maternal iodine intake affects iodine storage in the placenta and lactating mammary gland, which in turn affects thyroid function and BDNF and NSP-A expression in the offspring.

Associations of Habitual Mineral Intake with New-Onset Prediabetes/Diabetes after Acute Pancreatitis

Associations between habitual dietary intake of minerals and glucose metabolism have been extensively studied in relation to metabolic disorders. However, similar research has yet to be conducted in individuals after acute pancreatitis (AP). The main aim was to investigate the associations between habitual intake of 13 minerals and glycaemic status: new-onset prediabetes/diabetes after AP (NODAP), pre-existing prediabetes/type 2 diabetes (T2DM), and normoglycaemia after AP (NAP). Associations between the dietary intake of minerals and markers of glucose metabolism (glycated haemoglobin and fasting plasma glucose) were also studied. The EPIC-Norfolk food frequency questionnaire was used in a cross-sectional fashion to determine the habitual intake of 13 dietary minerals. ANCOVA as well as multiple linear regression analyses were conducted and five statistical models were built to adjust for covariates. The study included 106 individuals after AP. In the NODAP group, intake of 4 minerals was significantly less when compared with the NAP group: iron (B = -0.076, p = 0.013), nitrogen (B = -0.066, p = 0.003), phosphorous (B = -0.046, p = 0.006), and zinc (B = -0.078, p = 0.001). Glycated haemoglobin was significantly associated with iodine intake (B = 17.763, p = 0.032) and manganese intake (B = -17.147, p = 0.003) in the NODAP group. Fasting plasma glucose was significantly associated with manganese intake (B = -2.436, p = 0.027) in the NODAP group. Habitual intake of minerals differs between individuals with NODAP, T2DM, and NAP. Prospective longitudinal studies and randomised controlled trials are now warranted to further investigate the associations between mineral intake and NODAP.

Thyroid Profile and Factors Associated with Hypothyroidism Among Multidrug-Resistant Tuberculosis Patients Attending Saint Peter's Specialized Hospital Addis Ababa, Ethiopia

Background

The emergence of MDR-TB is a global public health problem. Hypothyroidism is one of the severe adverse drug reactions (ADRs) in MDR-TB patients on treatment. Representative data on hypothyroidism and its associated factors among MDR-TB patients are lacking.

Objective

To determine thyroid profiles and associated risk factors among multidrug-resistant TB patients during therapy with anti-MDR-TB regimen in Saint Peter Specialized Hospital Addis Ababa, Ethiopia from January to November 2020.

Methods

A cross-sectional study was conducted in MDR-TB patients in Addis Ababa, Ethiopia. A total of 162 patients, who were older than 18 years, had bacteriologically confirmed MDR-TB and on treatment for more than one month were enrolled consecutively from the TB registration book. However, critically sick patients and those who were receiving additional drugs known to cause severe ADRs were excluded. Simple descriptive statistics were used to present the socio-demographic and clinical characteristics of the patients. A logistic regression model was used to assess the association between independent and dependent variables. A p-value <0.05 was considered as statistically significant in all analyses.

Results

Mean age of the study participant was 35.9 ± 13.6 years. The prevalence of hypothyroidism was 32 (19.8%). The presence of co-morbidity, being underweight, and prothionamide use were significantly associated with hypothyroidism in MDR-TB patients on treatment.

Conclusion

Hypothyroidism occurs commonly among MDR-TB patients. Presence of co-morbidity, being underweight, and prothionamide drug use are the factors associated with hypothyroidism. Monitoring of thyroid function test during MDR-TB treatment and factors associated with hypothyroidism require attention to prevent complication.

Association of breastfeeding with thyroid function and autoimmunity in postmenopausal women

OBJECTIVE

Whether breastfeeding influences thyroid function and autoimmunity is not elucidated. We examined the association of history of breastfeeding with thyroid hormones and thyroperoxidase antibody (TPOAb).

DESIGN

Cross-sectional study of data from the 2013-2015 Korea National Health and Nutrition Examination Survey.

METHODS

A total of 816 postmenopausal women were stratified into three groups according to the duration of breastfeeding and number of breastfed children. Thyroid hormones levels, TPOAb titers, and the prevalence of hypothyroidism and TPOAb positivity were evaluated in each group.

RESULTS

Subjects with a history of prolonged breastfeeding had lower levels of thyrotropin (TSH) and TPOAb than the others. After adjusting for multiple confounding factors, the estimated means of TSH and TPOAb were associated with cumulative duration of breastfeeding. Duration of breastfeeding per child was associated with TSH levels, and number of breastfed children was associated with TPOAb titers. The odds ratio (OR) of hypothyroidism was significantly lower in group for ≥36 months of cumulative duration of breastfeeding, and the OR of TPOAb positivity was significantly lower in group with ≥3 breastfed children. In addition, duration of breastfeeding and the number of breastfed children were linearly correlated with log TSH and TPOAb each other in the multivariate model.

CONCLUSIONS

The present study showed that prolonged breastfeeding was inversely associated with TSH and the prevalence of hypothyroidism. Moreover, TPOAb and the prevalence of TPOAb positivity were inversely associated with number of breastfed children. These results indicate that breastfeeding may exert a protective effect on thyroid function and autoimmunity.

Association between urinary sodium levels and iodine status in Korea

BACKGROUND/AIMS

To evaluate the association between the urinary sodium concentration and iodine status in different age groups in Korea.

METHODS

This nationwide, population-based, cross-sectional study used data from the Korean National Health and Nutrition Examination Survey (VI 2-3, 2014 to 2015). We included 3,645 subjects aged 10 to 75 years with normal kidney function and without a history of thyroid disease. Adequate iodine intake was defined as a urinary iodine/creatinine (I/Cr) ratio of 85 to 220 µg/g. The urinary sodium/ creatinine (Na/Cr) ratios were classified as low (< 47 mmol/g), intermediate (47 to 114 mmol/g), or high (> 114 mmol/g).

RESULTS

The median urinary iodine concentration (UIC) was 292 µg/L (interquartile range [IQR], 157 to 672), and the median urinary I/Cr ratio was 195 µg/g (IQR, 104 to 478). Iodine deficiency (< 100 µg/L) and iodine excess (> 300 µg/L) were observed in 11.3% and 49.0% of subjects, respectively. The UIC was significantly associated with the urinary sodium concentration, and the urinary I/Cr ratio was significantly correlated with the urinary Na/Cr ratio (both p < 0.001). The distributions of UIC, urinary I/Cr ratio, and Na/Cr ratio varied among age groups. Low urinary I/Cr and Na/Cr ratios were most common in young adults (age, 19 to 29 years), while high urinary I/Cr and Na/Cr ratios were most common in elderly people (age, 60 to 75 years).

CONCLUSION

Iodine intake was significantly associated with sodium intake in the Korean population. Our study suggested that an adequately low salt intake might be helpful for preventing iodine excess in Korea.

Association between iodine intake and thyroid autoantibodies: a cross-sectional study of 7073 early pregnant women in an iodine-adequate region

PURPOSE

The association between iodine intake and thyroid autoimmunity has been debated, especially in pregnant women. This study aimed to investigate thyroid autoantibodies and their association with iodine intake and hypothyroidism in early pregnancy.

METHODS

7073 early pregnant women from an iodine-sufficient region participated in this study. Urinary iodine concentrations (UICs) were measured using an ammonium persulfate method. Serum thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb), thyroid-stimulating hormone (TSH), free thyroxine (FT4), and Tg were determined using an electrochemiluminescence immunoassay.

RESULTS

Iodine deficiency (UIC < 100 μg/L) was associated with higher risks of TPOAb positivity [adjusted odds ratio (aOR) = 1.64, 95% confidence interval [CI] (1.29-2.08)] and TgAb positivity [aOR = 1.44, 95% CI (1.16-1.80)]. Women with isolated TPOAb positivity, isolated TgAb positivity, or both TPOAb and TgAb positivity had a 14.64-fold, 7.83-fold, and 44.69-fold increased risk of overt hypothyroidism, and a 4.36-fold, 2.86-fold, and 6.26-fold increased risk of subclinical hypothyroidism, respectively. Moreover, the risks of overt and subclinical hypothyroidism in women with a high TPOAb titer were 16.99 and 4.80 times that in TPOAb-negative women, respectively. The risk of overt hypothyroidism in women with a high TgAb titer was 6.97 times that in TgAb-negative women.

CONCLUSIONS

Our work demonstrates that iodine deficiency during early pregnancy is an independent risk factor for both TPOAb positivity and TgAb positivity. Furthermore, positivity for both autoantibodies and a high thyroid autoantibody titer are associated with significantly higher risks of overt and subclinical hypothyroidism.

Association between Iodine Nutrition Status and Thyroid Disease-Related Hormone in Korean Adults: Korean National Health and Nutrition Examination Survey VI (2013-2015)

This study aimed to observe the relationship between iodine nutrition status (dietary iodine intake and estimated iodine intake based on urinary iodine concentration (UIC)) and thyroid disease-related hormones. This study involved 6090 subjects >19 years old with valid UIC, assessed between 2013 and 2015 by the Korean National Health and Nutrition Examination Survey, using a stratified, multistage, clustered probability-sampling design. The estimated iodine intake in participants was measured using UIC and urine creatinine. To examine the effect of iodine intake on thyroid disease, the iodine intake was divided into Korean Dietary Reference Intakes groups, and logistic regression analysis was performed via the surveylogistic procedure to obtain odds ratios (ORs) and 95% confidence intervals (CIs). The estimated iodine intake showed a significant positive correlation with dietary iodine intake (r = 0.021, p < 0.001), UIC (r = 0.918, p < 0.001), and thyroid-stimulating hormone (TSH) (r = 0.043, p < 0.001), but a significant negative correlation with free thyroxine (FT4) (r = -0.037, p < 0.001). Additionally, as the estimated iodine intake increased, age, TSH, and UIC increased, but FT4 decreased (p for trend < 0.0001). The risk of thyroid disease was higher in the "≥tolerable upper intake level (UL ≥ 2400 µg/day)" group than in the " Collapse

Key Words

• Korean
• epidemiologic studies
• iodine nutrition status
• thyroid disease
• thyrotropin
• urine iodine

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MESH Headings

• Adult
• Female
• Health Surveys
• Humans
• Iodine/administration & dosage
• Male
• Nutritional Status
• Republic of Korea/epidemiology
• Thyroid Diseases/epidemiology
• Thyroid Diseases/metabolism
• Thyroid Hormones
• Young Adult

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Affiliation(s)

Sohye Kim Department of Medical Nutrition, Graduate School of East-West Medical Science, Kyung Hee University, Yongin 17104, Korea; Nutrition Care Services, Seoul National University of Bundang Hospital, Seongnam 13620, Korea
Yong Seok Kwon F&D Communication, Gyeonggi 10433, Korea;
Ju Young Kim Department of Family Medicine, Seoul National University of Bundang Hospital, Seongnam 13620, Korea;
Kyung Hee Hong Department of Food Science and Nutrition, Dongseo University, Pusan 47011, Korea;
Yoo Kyoung Park Department of Medical Nutrition, Graduate School of East-West Medical Science, Kyung Hee University, Yongin 17104, Korea;

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Excessive Iodine Intake and Subclinical Hypothyroidism in Children and Adolescents Aged 6-19 Years: Results of the Sixth Korean National Health and Nutrition Examination Survey, 2013-2015

BACKGROUND

Iodine is an important element for the synthesis of thyroid hormone, and its deficiency or excessive intake is associated with various thyroid diseases. Little is known about the association between iodine status and thyroid function among children and adolescents living in iodine-rich areas. Therefore, this study analyzed this association using data from a nationwide survey.

METHODS

From the Korea National Health and Nutrition Examination Surveys VI (2013-2015) data, 1288 subjects (711 male) aged 6-19 years who underwent a urinary iodine concentration (UIC) test and 1000 subjects (564 male) aged 10-19 years who underwent a thyroid function test were included in this study. Serum levels of thyrotropin (TSH), free thyroxine (fT4), and thyroperoxidase antibodies (TPOAb) were analyzed. Subclinical hypothyroidism (SCH) was defined as TSH >5.5 μIU/mL with a normal fT4 level. Median daily iodine intake was calculated from the UIC. Daily sodium intake was derived from the nutritional survey data of 1181 subjects.

RESULTS

The median UIC was 449 μg/L (range 15-21,905 μg/L), and the prevalence rates of UIC ≥300 μg/L and ≥1000 μg/L were 64.9% and 25.0%, respectively. The prevalence rates of a sodium intake >2000 mg/day and iodine intake >2400 μg/day were 75.0% (885/1181) and 12.7% (164/1288), respectively. The prevalence rates of SCH and TPOAb >34 IU/mL were 7.2% (72/1000) and 2.3% (23/1000), respectively. The prevalence of SCH was significantly higher in the iodine deficient and iodine excess groups compared to those in the UIC 100-299.9 μg/L group (p = 0.038). Therefore, there was a U-shaped and inverted U-shaped correlation between serum levels of TSH and fT4 with UIC, respectively. These correlations were especially prominent when UIC was >1000 μg/L. There was no definite correlation between TPOAb and UIC.

CONCLUSIONS

Excess iodine was prevalent in Korean children and adolescents, and it may be associated with SCH. Therefore, monitoring the iodine status and education on adequate intake are needed in iodine-rich areas.

Assessment of thyroid function in children, adults and pregnant and lactating women after long-term salt iodisation measurements

Universal salt iodisation (USI) has been successfully implemented in China for more than 15 years. Recent evidence suggests that the definition of 'adequate iodine' (100-199 µg/l) be revised to 'sufficient iodine' (100-299 µg/l) based on the median urinary iodine concentration (MUI) in school-age children. The objective of this study was to determine the prevalence of thyroid dysfunction in populations after long-term salt iodisation and examine whether the definition of adequate iodine can be broadened to sufficient iodine based on the thyroid function in four population groups. A cross-sectional survey was conducted in six provinces in the northern, central and southern regions of China. Four population groups consisting of 657 children, 755 adults, 347 pregnant women and 348 lactating women were recruited. Three spot urinary samples were collected over a 10-d period and blood samples were collected on the 1st day. In the study, among the adults, pregnant women and lactating women, the prevalence rates of elevated thyroglobulin antibody and thyroid microsomal antibody levels were 12·4, 8·5 and 7·8 %, and 12·1, 9·1 and 9·1 %, respectively. Abnormally high thyroid dysfunction prevalence was not observed after more than 15 years of USI in China because the thyroid dysfunction rates were all <5 %. The recommended range should be cautiously broadened from adequate iodine to sufficient iodine according to the MUI of school-age children considering the high levels of hormones and antibodies in the other populations. Adults, particularly pregnant women positive for thyroid antibodies, should be closely monitored.

Gestational Age-specific Cut-off Values Are Needed for Diagnosis of Subclinical Hypothyroidism in Early Pregnancy

During the first trimester of pregnancy, thyroid-stimulating hormone (TSH) >2.5 mIU/L has been suggested as the universal criterion for subclinical hypothyroidism. However, TSH levels change continuously during pregnancy, even in the first trimester. Therefore the use of a fixed cut-off value for TSH may result in a different diagnosis rate of subclinical hypothyroidism according to gestational age. The objective of this study was to obtain the normal reference range of TSH during the first trimester in Korean gravida and to determine the diagnosis rate of subclinical hypothyroidism using the fixed cut-off value (TSH >2.5 mIU/L). The study population consisted of pregnant women who were measured for TSH during the first trimester of pregnancy (n=492) and nonpregnant women (n=984). Median concentration of TSH in pregnant women was lower than in non-pregnant women. There was a continuous decrease of median TSH concentration during the first trimester of pregnancy (median TSH concentration: 1.82 mIU/L for 3+0 to 6+6 weeks; 1.53 mIU/L for 7+0 to 7+6 weeks; and 1.05 mIU/L for 8+0 to 13+6 weeks). Using the fixed cut-off value of TSH >2.5 mIU/L, the diagnosis rate of subclinical hypothyroidism decreased significantly according to the gestational age (GA) at TSH (25% in 3+0 to 6+6 weeks, 13% in 7+0 to 7+6 weeks, and 9% for 8+0 to 13+6 weeks, P<0.001), whereas the diagnosis rate was 5% in all GA with the use of a GA-specific cut-off value (P=0.995). Therefore, GA-specific criteria might be more appropriate for the diagnosis of subclinical hypothyroidism.

Effects of potassium iodide in concentrations of TSH, tT3 and tT4 in serum of subjects with sporotrichosis

The saturated potassium iodide solution (SSKI) as treatment for sporotrichosis may cause hypothyroidism by suppressing the synthesis of thyroid hormones (tT3 and tT4 ) and the iodine excess could lead to thyrotoxicosis. Evaluating the changes in serum levels of TSH, tT3 and tT4 in euthyroid patients with sporotrichosis treated with SSKI. For the selection of euthyroid patients, TSH, tT3 and tT4 concentrations were measured for those adults and children diagnosed with sporotrichosis. Each paediatric patient was administered SSKI orally in increasing doses of 2-20 drops/3 times/day and 4-40 drops/3 times/day in adults. Serum concentrations of TSH, tT3 and tT4 were measured 20 days after started the treatment and 15 days posttreatment. Eight euthyroid patients aged between 2 to 65 years old were included. After 20 days of treatment, two suffered subclinical hypothyroidism, one developed subclinical hyperthyroidism, and one hyperthyroxinaemia euthyroid. At 15 days posttreatment only four patients were evaluated and all serum levels of TSH, tT3 and tT4 were normal. Some euthyroid patients with sporotrichosis can develop hyperthyroidism or subclinical iodine-induced hypothyroidism, during the administration of 3 or 6 g SSKI/day.

Iodine and thyroid function

Severe iodine deficiency causes hypothyroidism that results in impaired somatic growth and motor development in children. Mild and moderate iodine deficiencies cause multifocal autonomous growth of thyroid, which results in thyrotoxicosis. On the other hand, iodine excess is associated with the development of hypothyroidism and thyroid autoimmunity. In areas of iodine deficiency, a sudden increase in iodine intake is associated with transient hyperthyroidism. Recent studies demonstrated that long-term thyroid function of subjects who experienced both iodine deficiency and iodine excess during childhood tended to be abnormal despite optimization of their current iodine intake. Iodine status in the Korean Peninsula is very unique because people in the Republic of Korea have been shown to have predominantly excessive iodine levels, whereas the Democratic People's Republic of Korea is known to be an iodine-deficient area. Further research is warranted to verify the optimal ranges of iodine intake and to clarify the effects of iodine intake on thyroid disorders in the Korean Peninsula.

Longitudinal trends in thyroid function in relation to iodine intake: ongoing changes of thyroid function despite adequate current iodine status

OBJECTIVE

Several cross-sectional studies on populations with iodine deficiency showed that TSH-levels are negatively associated with age, while in populations with high iodine intake TSH is positively associated with age. The question is whether such an age-thyroid function relation is an ongoing process apparent also in longitudinal studies and whether it reflects an actual iodine deficiency or an iodine insufficiency in the past.

METHODS

In an area with a borderline iodine status in the past, we studied 980 participants of the Nijmegen Biomedical Study. We measured serum TSH, free thyroxine (FT₄), total triiodothyronine (T₃), peroxidase antibodies, and the urine iodine and creatinine concentration 4 years after our initial survey of thyroid function, in which we reported a negative association between TSH and age.

RESULTS

within 4 years, TSH decreased by 5.4% (95% ci 2.58.3%) and FT₄ increased by 3.7% (95% ci 2.94.6%). median urinary iodine concentration was 130 μg/l. estimated 24-h iodine excretion was not associated with TSH, T₃, change of TSH, or FT₄ over time or with the presence of antibodies against thyroid peroxidase. Only FT₄ appeared to be somewhat higher at lower urine iodine levels: a 1.01% (95% CI 0.17-1.84%) higher FT₄ for each lower iodine quintile.

CONCLUSIONS

In this longitudinal study, we found an ongoing decrease in TSH and increase in FT₄ in a previously iodine insufficient population, despite the adequate iodine status at present. This suggests that low iodine intake at young age leads to thyroid autonomy (and a tendency to hyperthyroidism) that persists despite normal iodine intake later in life.

Effect of maternal excessive iodine intake on neurodevelopment and cognitive function in rat offspring

Background

Iodine deficiency and iodine excess are both associated with adverse health consequences. Iodine deficiency during pregnancy leads to insufficient maternal thyroid hormone, subsequently causing irreversible adverse effects on the neurological and cognitive functions of the offspring. The results of our previous epidemiological study suggested that mild iodine excess might increase the prevalence of subclinical hypothyroidism. In the present study, female Wistar rats maintained on low-iodine grain were randomly assigned to three groups based on iodated water concentration: low iodine (LI, 1.2 μg/d), normal iodine (NI, 5–6 μg/d), and 3-fold high iodine (3HI, 15–16 μg/d). The present study investigated whether higher-than-normal iodine intake (3HI) by rats from before pregnancy until breastfeeding affects the postnatal (PN) neurodevelopment (PN7 and PN45) of their offspring during particularly sensitive periods in brain development.

Results

After 12 weeks of treatment (before pregnancy), iodine concentrations in urine and thyroid tissue and circulating thyroxine of adult females correlated with iodine intake. Brain-derived neurotrophic factor (BDNF) expression in the hippocampi of pups on PN7 and PN45 was decreased in 3HI group compared to the NI controls (P < 0.05, all) On PN7 and PN45, the BDNF levels of the 3HI pups were 83.5% and 88.8%, respectively, that of the NI pups. In addition, the 3HI group had a higher neuroendocrine-specific protein A (NSP-A) level than the NI controls on PN7 (P < 0.05). NSP-A levels of the 3HI pups were 117.0% that of the NI pups. No significant difference was observed in the expressions of c-Fos or c-Jun in the hippocampal CA1 region of the 3HI group compared to the controls (P > 0.05). Results from the Morris water maze test revealed that pups of the 3HI group had mild learning and spatial memory deficits.

Conclusions

The neurodevelopmental and cognitive deficits of the 3HI pups were mild and temporary, likely related to the changes in hippocampal protein expressions of BDNF and NSP-A.