The influence of extended fasting on thyroid hormone: local and differentiated regulatory mechanisms.

The hypometabolism induced by fasting has great potential in maintaining health and improving survival in extreme environments, among which thyroid hormone (TH) plays an important role in the adaptation and the formation of new energy metabolism homeostasis during long-term fasting. In the present review, we emphasize the potential of long-term fasting to improve physical health and emergency rescue in extreme environments, introduce the concept and pattern of fasting and its impact on the body's energy metabolism consumption. Prolonged fasting has more application potential in emergency rescue in special environments. The changes of THs caused by fasting, including serum biochemical characteristics, responsiveness of the peripheral and central hypothalamus-pituitary-thyroid (HPT) axis, and differential changes of TH metabolism, are emphasized in particular. It was proposed that the variability between brain and liver tissues in THs uptake, deiodination activation and inactivation is the key regulatory mechanism for the cause of peripheral THs decline and central homeostasis. While hypothalamic tanycytes play a pivotal role in the fine regulation of the HPT negative feedback regulation during long-term fasting. The study progress of tanycytes on thyrotropin-releasing hormone (TRH) release and deiodination is described in detail. In conclusion, the combination of the decrease of TH metabolism in peripheral tissues and stability in the central HPT axis maintains the basal physiological requirement and new energy metabolism homeostasis to adapt to long-term food scarcity. The molecular mechanisms of this localized and differential regulation will be a key research direction for developing measures for hypometabolic applications in extreme environment.

The correlation between the thyroid function and urinary iodine/creatinine ratio of pregnant women attending a tertiary hospital in Beijing, China, during different trimesters.

OBJECTIVE: This study investigated the correlation between thyroid function and urinary iodine/creatinine ratio (UI/Cr) in pregnant women during different trimesters and explored potential influencing factors. METHODS: In this cross-sectional study, serum levels of thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4), and UI/Cr were measured in 450 pregnant women. Correlations were analyzed using Pearson's correlation coefficient and multiple linear regression. Subgroup analyses were performed based on age, body mass index (BMI), parity, gestational age, education, occupation, and family history of thyroid disorders. RESULTS: UI/Cr was positively correlated with FT4 levels in the first and second trimesters, particularly in women with older age, higher BMI, multiparity, higher education, and employment. No significant correlations were found between UI/Cr and TSH or FT3 levels. CONCLUSION: UI/Cr is positively correlated with FT4 levels in early pregnancy, especially in women with certain risk factors. Regular monitoring of iodine status and thyroid function is recommended for pregnant women to ensure optimal maternal and fetal health.

Age-Related Features of the Function of the Hypothalamic-Pituitary-Thyroid (HPT) Axis in Nonhuman Primates under Constant Lighting.

We studied the features of the functioning of the hypothalamic-pituitary-thyroid (HPT) axis under conditions of constant (4 weeks) lighting (LED lamps intended for office and residential premise) on a translational model of young adult and old female rhesus monkeys, in particular taking into account their behavior. Constant lightning had no significant effect on the levels of thyroid-stimulating hormone, thyroxine, and triiodothyronine under basal conditions in all animals, regardless of age and behavioral characteristics, but induced a decrease in thyroid function under conditions of its activation with thyrotropin-releasing hormone, mainly in old animals.

Fetal sexual dimorphism of maternal thyroid function parameters during pregnancy, a single center retrospective real-world study.

Introduction: Thyroid function during pregnancy fluctuates with gestational weeks, seasons and other factors. However, it is currently unknown whether there is a fetal sex-specific thyroid function in pregnant women. The purpose of this study was to investigate the fetal sex differences of maternal thyroid-stimulating hormone (TSH) and free thyroxine (FT4) in pregnant women. Methods: This single-center retrospective real-world study was performed by reviewing the medical records of pregnant women who received regular antenatal health care and delivered liveborn infants in Shanghai First Maternity and Infant Hospital (Pudong branch), from Aug. 18, 2013 to Jul. 18, 2020. Quantile regression was used to evaluate the relationship between various variables and TSH and FT4 concentrations. The quantile regression also evaluated the sex impact of different gestational weeks on the median of TSH and FT4. Results: A total of 69,243 pregnant women with a mean age of 30.36 years were included. 36197 (52.28%) deliveries were boys. In the three different trimesters, the median levels (interquartile range) of TSH were 1.18 (0.66, 1.82) mIU/L and 1.39 (0.85, 2.05) mIU/L, 1.70 (1.19, 2.40) mIU/L; and the median levels (interquartile range) of FT4 were 16.63 (15.16, 18.31) pmol/L, 14.09 (12.30, 16.20) pmol/L and 13.40 (11.52, 14.71) pmol/L, respectively. The maternal TSH upper limit of reference ranges was decreased more in mothers with female fetuses during gestational weeks 7 to 12, while their FT4 upper limit of the reference ranges was increased more than those with male fetuses. After model adjustment, the median TSH level was 0.11 mIU/L lower (P <0.001), and FT4 level was 0.14 pmol/L higher (P <0.001) for mothers with female fetuses than those with male fetuses during gestational weeks 9 to 12. Discussion: We identified sexual dimorphism in maternal thyroid function parameters, especially during 9-12 weeks of pregnancy. Based on previous research, we speculated that it may be related to the higher HCG levels of mothers who were pregnant with girls during this period. However, longitudinal studies are needed to determine if fetal sex differences impact the maternal thyroid function across pregnancy.

Relationship of Thyroid Volume and Function with Ankle-Brachial Index, Toe-Brachial Index, and Toe Pressure in Euthyroid People Aged 18-65.

Background and Objectives: The interrelationship between thyroid function and the state of the cardiovascular system has been investigated both in preclinical and human studies. However, it remains unclear whether there is any association between thyroid hormones and features of subclinical cardiovascular dysfunction in euthyroid patients. Material and Methods: This study involved 45 people (females: 57.8%) with no thyroid disease who, during planned hospitalization, underwent thyroid ultrasound, determination of biochemical parameters of thyroid function, and measurement of ankle-brachial index (ABI) and toe-brachial index (TBI). People with signs of acute illness or a deterioration of their health were excluded. Results: Significant correlations were found between free triiodothyronine (FT3) and several parameters of both ABI (R = 0.347; p = 0.019 for the mean ABI taken from right side and left side values) and TBI (R = 0.396; p = 0.007 for the mean TBI taken from right side and left side values), as well as the maximal toe pressure (TP) taken from right side and left side values (R = 0.304; p = 0.045). Thyrotropin (TSH) was shown to be significantly correlated only with the maximal TBI value (taken from right side and left side values) (R = 0.318; p = 0.033), whereas free thyroxin (FT4) was shown to be significantly correlated only with the minimal TBI value (taken from right side and left side values) (R = 0.381; p = 0.01). Thyroid volume (TV) was shown to be correlated with TP (R = 0.4; p = 0.008 for the mean TP taken from right side and left side values) and some parameters of TBI value (R = 0.332; p = 0.028 for the mean TBI taken from right side and left side values), but no significant correlations were found between TVand ABI parameters. Patients with a mean ABI value ≤ 1.0 or a mean TBI value ≤ 0.75 have lower TSH, FT3, FT4, and TV than the rest of the study population, but the difference was statistically significant only for FT3. Conclusions: Even in a population of euthyroid patients with no diagnosed thyroid disease, there are some significant correlations between the volume and function of the thyroid gland and the selected features of subclinical cardiovascular dysfunction such as ABI and TBI.

Establishment of reference intervals of thyroid-related hormones for adults with normal liver function in Zhejiang Province by indirect method.

Objective: Thyroid disorders are prevalently diagnosed yet face significant challenges in their accurate identification in China. Predominantly, the reference intervals (RIs) currently in use across Chinese medical facilities derive from company-provided data, lacking stringent scientific validation. This practice underscores the urgent necessity for establishing tailored RIs for thyroid-related hormones, specifically tailored to the coastal area populations. Such refined RIs are imperative for empowering clinicians with the precise tools needed for the accurate diagnosis of both overt and subclinical thyroid conditions. Methods: This investigation analyzed the medical histories of 6021 euthyroid individuals mainly from East coastal area of China between June 2019 and December 2020. The cohort comprised residents of coastal areas, focusing on extracting insights into the regional specificity of thyroid hormone levels. A thorough examination protocol was implemented, encompassing inquiries into thyroid health history, ultrasound screenings, palpations during thyroid surgery, detections of thyroid antibodies, and reviews of medication histories. Adherence to the CLSI C28-A3 guidelines facilitated the derivation of RIs for thyroid-related hormones, subsequently juxtaposed against those provided by commercial entities. Results: The study delineated the following gender- and age-specific RIs for Thyroid-Stimulating Hormone (TSH): for males under 50 years, 0.57-3.37; males over 50 years, 0.51-4.03; females under 50 years, 0.53-3.91; and females over 50 years, 0.63-4.31. Further analysis revealed the RIs for Free Thyroxine (FT4), Free Triiodothyronine (FT3), Total Thyroxine (TT4), and Total Triiodothyronine (TT3) amongst males and females, with notable distinctions observed between the two genders and across age brackets. These findings are in stark contrast to the standardized intervals provided by manufacturers, particularly highlighting differences in TT3 and FT3 levels between genders and a tendency for TSH levels to increase with age. Conclusion: This research successfully establishes refined RIs for thyroid-related hormones within the Chinese coastal area populations, taking into account critical demographic factors such as gender and age. These tailored RIs are anticipated to significantly enhance the diagnostic accuracy for thyroid diseases, addressing the previously noted discrepancies with manufacturer-provided data and underscoring the importance of regionally and demographically adjusted reference intervals in clinical practice.

The Role of Nutrition on Thyroid Function.

Thyroid function is closely linked to nutrition through the diet-gut-thyroid axis. This narrative review highlights the influence of nutritional components and micronutrients on thyroid development and function, as well as on the gut microbiota. Micronutrients such as iodine, selenium, iron, zinc, copper, magnesium, vitamin A, and vitamin B12 influence thyroid hormone synthesis and regulation throughout life. Dietary changes can alter the gut microbiota, leading not just to dysbiosis and micronutrient deficiency but also to changes in thyroid function through immunological regulation, nutrient absorption, and epigenetic changes. Nutritional imbalance can lead to thyroid dysfunction and/or disorders, such as hypothyroidism and hyperthyroidism, and possibly contribute to autoimmune thyroid diseases and thyroid cancer, yet controversial issues. Understanding these relationships is important to rationalize a balanced diet rich in essential micronutrients for maintaining thyroid health and preventing thyroid-related diseases. The synthetic comprehensive overview of current knowledge shows the importance of micronutrients and gut microbiota for thyroid function and uncovers potential gaps that require further investigation.

Delta check limits for thyroid function tests adjusted for clinical settings.

BACKGROUND: This study aimed to determine practical delta check limits (DCLs) for thyroid function tests (TFTs) to detect sample misidentifications across various clinical settings. METHODS: Between 2020 and 2022, 610,437 paired TFT results were collected from six university hospitals. The absolute DCL (absDCL) was determined using the 95th percentile for each clinical setting from a random 60 % of the total data. These absDCLs were then tested within and across different settings using the remaining 40 % of the data, alongside mix-up datasets for result and sample comparisons. The sensitivities of absDCL were calculated within and across groups in the mix-up datasets. RESULTS: Health screening absDCLs were notably lower than in other settings (2.58 vs. 5.93-7.08 for thyroid-stimulating hormone; 4.12 vs. 8.24-10.04 for free thyroxine; 0.49 vs. 0.82-0.91 for total triiodothyronine). The proportion of results exceeding absDCL of health screening differed from those of other clinical settings. Furthermore, sensitivity between health screening and other clinical settings was significantly different in both the result mix-up and sample mix-up datasets. CONCLUSIONS: This study determined practical DCLs for TFTs and highlighted differences in absDCLs between health screening and other settings. These findings emphasize the importance of tailored DCLs in improving the accurate reporting of TFTs.

Retrospective Cross-Sectional Study of the Relationship of Thyroid Volume and Function with Anthropometric Measurements, Body Composition Analysis Parameters, and the Diagnosis of Metabolic Syndrome in Euthyroid People Aged 18-65.

Background and Objectives: The thyroid is a key endocrine gland for the regulation of metabolic processes. A body composition analysis (BCA) is a valuable complement to the assessment of body mass index, which is derived only from body weight and height. This cross-sectional retrospective study aimed to investigate the relationships between thyroid volume (TV) and thyroid function parameters, anthropometric measurements, BCA parameters, and the presence of metabolic syndrome (MetS) in adults without clinically overt thyroid disease. Material and Methods: This study involved 45 people (females: 57.8%; MetS: 28.9%) hospitalized for planned diagnostics without signs of acute illness or a deterioration of their health and without thyroid disease, who underwent thyroid ultrasound scans, biochemical tests to assess their thyroid function, MetS assessments, anthropometric measurements, and BCAs using the bioelectrical impedance method. Results: The TV was significantly larger in people with MetS compared to people without MetS. The TV was significantly higher and the serum thyrotropin (TSH) concentration was significantly lower in overweight and obese people than in normal and underweight people. The free triiodothyronine (FT3) serum concentration and TV were correlated with waist circumference and some parameters of the BCA, and the FT3 concentration was also correlated with the body mass index, waist-hip ratio, and waist-height ratio. No significant correlations were found between the FT4 and TSH and the results of the anthropometric and BCA measurements. Conclusions: Even in a population of euthyroid patients without clinically overt thyroid disease, there were some significant relationships between the volume and function of the thyroid gland and the results of their anthropometric parameters, BCAs, and the presence of MetS features.

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OBJECTIVES: To investigate the influencing factors and reference ranges for thyroid function in preterm infants at the age of 7 days, with the aim of avoiding unnecessary clinical reexamination and intervention. METHODS: A retrospective analysis was performed for the data of 685 preterm infants from January 2020 to January 2023. According to gestational age and birth weight, they were divided into a high-risk group (gestational age <34 weeks or birth weight<2 000 g; 228 infants) and a low-risk group (gestational age ≥34 weeks and birth weight ≥2 000 g;457 infants). The influencing factors for thyroid function were analyzed, and 95% reference range was calculated. RESULTS: Gestational age, birth weight, birth season, sex, and assisted reproduction were the influencing factors for thyroid function (P<0.05). For the preterm infants in the high-risk group, the reference ranges of free triiodothyronine (FT3), free thyroxine (FT4), total triiodothyronine (TT3), total thyroxine (TT4), and thyroid stimulating hormone (TSH) were 2.79-5.40 pmol/L, 8.80-25.64 pmol/L, 0.80-2.15 nmol/L, 50.06-165.09 nmol/L, and 0.80-18.57 µIU/mL, respectively. For those in the low-risk group, the reference ranges of these indicators were 3.08-5.93 pmol/L, 11.17-26.24 pmol/L, 1.02-2.27 nmol/L, 62.90-168.95 nmol/L, and 0.69-13.70 µIU/mL, respectively. FT3, FT4, TT3, and TT4 were positively correlated with gestational age (P<0.05); FT3, FT4, TT3, and TT4 were positively correlated with birth weight (P<0.05); TSH was negatively correlated with birth weight (P<0.05). CONCLUSIONS: Thyroid function in preterm infants at the age of 7 days is affected by the factors such as gestational age and birth weight, and the reference ranges of thyroid function in preterm infants at the age of 7 days should be established based on gestational age and birth weight.

Iodine nutritional status and its associations with thyroid function of pregnant women and neonatal TSH.

Introduction: Iodine serves as a crucial precursor for the synthesis of thyroid hormones and plays an import role in both pregnant women and their offspring. The relationships between iodine nutritional status and maternal thyroid function and neonatal outcomes remain inconclusive in areas with adequate iodine nutrition. This study aims to investigate their correlations. Methods: Blood, morning urine and 24-hour urine were collected from the pregnant women to measure thyroid functions, serum iodine concentration (SIC), morning urine iodine concentration (UIC) and 24-hour urine iodine excretion (24-hour UIE). Indicators of their offspring's neonatal indexes were recorded. Results: A total of 559 pregnant women were enrolled in this study. The iodine indicators including Tg, 24-hour UIE and morning UIC were significantly different among the euthyroid pregnant women and those with different thyroid disorders. The levels of FT3, FT4, and SIC exhibited a gradual decline and the concentration of TSH exhibited a gradual increase trend throughout the progression of pregnancy in euthyroid pregnant women. There were no significant differences in neonatal outcomes and neonatal TSH values among euthyroid pregnant women and thyroid disorders pregnant women. SIC had a significant impact on maternal FT4 levels throughout all three trimesters, with varying degrees of importance observed in each trimester. TSH level emerged as the primary determinant of FT4 during the first trimester, while SIC exerted a predominant influence on FT4 levels in the second and third trimesters. The prevalence of thyroid disorders in pregnant women was the lowest when the SIC of pregnant women was probable in the range of 60~70 µg/L, 24-hours UIE was in the range of 250~450 µg, and Tg was in the range of 9~21 µg/L. Maternal TSH exhibited a notable influence on neonatal TSH levels, particularly at the 50th and 75th quantiles. Among the iodine nutritional indicators, SIC and morning UIC demonstrated higher AUC values for abnormal FT4 and TSH, respectively. Discussion: The iodine nutrition status of pregnant women exerts an impact on their thyroid function and prevalence of thyroid disorders, and neonatal TSH was affected by maternal TSH. SIC may be a better indicator for iodine nutritional assessment than other indexes.

Thyroid function and iodine intake: global recommendations and relevant dietary trends.

Iodine is a micronutrient that is essential for thyroid hormone production. Adequate iodine intake is especially important during pregnancy and early life, when brain development is dependent on thyroid hormones. Iodine intake recommendations vary around the world, but most recommendations generally reflect the increased requirements during pregnancy and lactation, although adequate iodine intake before pregnancy is also important. Tremendous progress has been made in improving iodine intake across the world over the past 30 years, mainly through salt-iodization programmes. However, in countries without strong iodine fortification programmes, and with shifts in dietary patterns, a need has arisen for health organizations, governments and clinicians to ensure that adequate iodine is consumed by everyone in the population. For example, in countries in which adequate iodine intake depends on individual food choice, particularly of iodine-rich milk and dairy products, intake can be highly variable and is also vulnerable to changing dietary patterns. In this Review, iodine is considered in the wider context of the increasing prevalence of overweight and obesity, the dietary trends for salt restriction for cardiovascular health and the increasing uptake of plant-based diets.

Thyroid function variations within the reference range and cognitive function: A two-sample Mendelian randomization study.

BACKGROUND: The causal relationship between thyroid function variations within the reference range and cognitive function remains unknown. We aimed to explore this causal relationship using a Mendelian randomization (MR) approach. METHODS: Summary statistics of a thyroid function genome-wide association study (GWAS) were obtained from the ThyroidOmics consortium, including reference range thyroid stimulating hormone (TSH) (N = 54,288) and reference range free thyroxine (FT4) (N = 49,269). GWAS summary statistics on cognitive function were obtained from the Social Science Genetic Association Consortium (SSGAC) and the UK Biobank, including cognitive performance (N = 257,841), prospective memory (N = 152,605), reaction time (N = 459,523), and fluid intelligence (N = 149,051). The primary method used was inverse-variance weighted (IVW), supplemented with weighted median, Mr-Egger regression, and MR-Pleiotropy Residual Sum and Outlier. Several sensitivity analyses were conducted to identify heterogeneity and pleiotropy. RESULTS: An increase in genetically associated TSH within the reference range was suggestively associated with a decline in cognitive performance (ß = -0.019; 95%CI: -0.034 to -0.003; P = 0.017) and significantly associated with longer reaction time (ß = 0.016; 95 % CI: 0.005 to 0.027; P = 0.004). Genetically associated FT4 levels within the reference range had a significant negative relationship with reaction time (ß = -0.030; 95%CI:-0.044 to -0.015; P = 4.85 × 10-5). These findings remained robust in the sensitivity analyses. CONCLUSIONS: Low thyroid function within the reference range may have a negative effect on cognitive function, but further research is needed to fully understand the nature of this relationship. LIMITATIONS: This study only used GWAS data from individuals of European descent, so the findings may not apply to other ethnic groups.

Association between physical activity and thyroid function in American adults: a survey from the NHANES database.

OBJECTIVE: Physical activity (PA) is closely related to our lives, and the effects of PA on thyroid function have not been elucidated. METHODS: Using data from the National Health and Nutrition Examination Survey (NHANES) 2007-2012, we included 5877 participants and analyzed the associations of thyroid function with weekly physical activity (PAM, expressed in metabolic equivalents of task) and physical activity time (PAT) in American adults. Univariate and multivariate logistic analyses were used to demonstrate the associations of PAM and PAT with the primary outcome. Linear regression analysis was performed to determine the associations between thyroid biochemical indicators/diseases and PAM/PAT. RESULTS: Our study revealed noticeable sex differences in daily PA among the participants. The odds ratio of the fourth versus the first quartile of PAM was 3.07 (confidence interval, CI [1.24, 7.58], p = 0.02) for overt hypothyroidism, 3.25 (CI [1.12, 9.45], p = 0.03) for subclinical hyperthyroidism in adult men. PAT in the range of 633-1520 min/week was found to be associated with the occurrence of subclinical hyperthyroidism [p < 0.001, OR (95% CI) = 5.89 (1.85, 18.80)], PAT of the range of > 1520 min/week was found to be associated with the occurrence of overt hypothyroidism [p < 0.001, OR (95% CI) = 8.70 (2.80, 27.07)] and autoimmune thyroiditis (AIT) [p = 0.03, OR (95% CI) = 1.42 (1.03, 1.97)] in adult men. When PAM < 5000 MET*minutes/week or PAT < 1000 min/week, RCS showed an L-shaped curve for TSH and an inverted U-shaped curve for FT4. The changes in FT3 and TT3 in men were linearly positively correlated with PAM and PAT, while TT4 is linearly negatively correlated. CONCLUSION: The amount of daily physical activity of American adults is strongly associated with changes in thyroid function, including thyroid hormone levels and thyroid diseases. Thyroid hormone levels were varied to a certain extent with changes in PAM and PAT.

The relationship between dietary total flavonoids and thyroid function in U.S.adults, NHANES 2007-2010.

BACKGROUND: Although small studies have shown that flavonoids can affect thyroid disease, few epidemiological studies have explored the relationship between dietary total flavonoids (TFs) intake and serum thyroid function. The aim of this research was to evaluate the relationship between TFs and serum thyroid function. METHODS: Our study included 4,949 adults from the National Health and Nutrition Examination Survey (NHANES) 2007-2010. Multivariable linear regression, subgroup analyses, and interaction terms were used to explore the relationships between TFs and thyroid function. And we also used restricted cubic splines (RCS) to investigate possible nonlinear relationships. RESULTS: After adjusting for covariates, we found that log10-transformated dietary total flavonoids intake (LgTFs) was negatively associated with total thyroxine (TT4) (ß = -0.153, 95% CI = -0.222 to -0.084, P<0.001). Subgroup analyses revealed a stronger and statistically supported association in subjects with high annual family income (ß = -0.367, P<0.001, P for interaction = 0.026) and subjects with high poverty to income ratio (PIR) (ß = -0.622, P<0.001, P for interaction = 0.042). And we found a U-shaped curve association between LgTFs and free triiodothyronine (FT3) (inflection point for LgTFs: 2.063). CONCLUSION: The results of our study demonstrated that a higher intake of total flavonoids in the diet was negatively associated with a lower TT4. Furthermore, the associations were more pronounced in high annual family income and high PIR adults. And we found a U-shaped relationship between LgTFs and FT3. These findings provided guidance for future thyroid dysfunction diet guidelines.

A Horizontal and Longitudinal Study on the Changes of Aging Thyroid Function in Elderly Male Population.

OBJECTIVES: There are few follow-up studies on thyroid function in the same group for many years. Therefore, the purpose of this study was to retrospectively analyze the changes of thyroid function in a group of people for 8 years and to explore the changes of thyroid function in elderly men with normal thyroid function with age. METHODS: Reviewing the records of elderly men who underwent physical examination in the Beijing Hospital physical examination center from 2013 to 2020, 354 subjects were included in the study. According to age, they are divided into 4 groups. The differences in thyrotropin (TSH), anti-triiodothyronine (rT3), free triiodothyronine (FT3), and free thyroid hormone (FT4) among different age groups in initial time (2013) were compared. Longitudinal comparison of changes of thyroid function in the same age group for 8 years was compared too. RESULTS: At the initial time, age was negatively correlated with FT3 (r = 0.349, p < 0.001), positively correlated with rT3 and TSH (r = 0.182, p < 0.001, r = 0.212, p < 0.001), but not correlated with FT4. The results of eight years of analysis show that, for TSH, during the whole follow-up period, the TSH of the >80 years group was higher than that of the <60 years and 60-69 years groups, and the difference was statistically significant. The 70-79 age group was higher than the <60 years group at different time points, except for the age group <60 years. The other three groups showed an increasing trend with age, especially in the group of ≥80 years. For FT3, in 2013, the age ≥80 years group was significantly lower than that of the 70-79 years, 60-69 years, and <60 years old groups (p < 0.05). The analysis results at different time points in each age group showed a downward trend and then an upward trend. For FT4, there was no significant difference in FT4 among different age groups in 2013. Still, during the follow-up period, the age group ≥80 was lower than other age groups in 2019 and lower than the <60 years groups in 2014, 2015, 2019, and 2020, and the difference was statistically significant. The change rule of FT4 with the increase of age was not clear. For rT3, during the whole follow-up period, the rT3 of the >80 years group was higher than that of the <60 years and 60-69 years groups, and the difference was statistically significant. The analysis results at different time points in each age group showed a trend of rising first, then falling, and finally rising. After 2017, the rT3 of the 70-79 years and ≥80 years groups increased with age. CONCLUSIONS: The thyroid function index of elderly men changes with age. In transverse analysis, the value of TSH is the highest, and FT3 is the lowest in the group ≥80 years old. There are differences between the changes in the longitudinal analysis and the results of the horizontal analysis. Therefore, the law of thyroid function changing with age in different individuals is not the same as that of the same individual with age, which should be paid more attention in medical research and clinical diagnosis and treatment.

Assessment of iodine nutritional status and gestational thyroid function reference ranges during the first trimester of pregnancy in Taiwan.

BACKGROUND: Iodine nutrition is critical for fetal neurodevelopment in the first trimester of pregnancy, a period associated with dramatic changes in thyroid function. The aim of this study was to evaluate iodine nutritional status and thyroid function reference ranges in the first trimester in Taiwan. METHODS: Pregnant women aged 20 years and above in the first trimester were recruited in Taipei Veterans General Hospital, Taiwan from March 2019 to July 2022. Each participant provided a spot urine sample for measurement of urinary iodine concentration (UIC) and a blood sample for checkup of thyroid function and thyroid autoantibodies. A simple food frequency questionnaire was also completed. RESULTS: A total of 209 women with a mean age of 32.9 ± 4.4 years were enrolled. The median UIC was 160.9 µg/L (interquartile range [IQR]: 105.0-246.2 µg/L), indicating overall iodine sufficiency. The gestational thyroid function reference ranges were: thyroid stimulating hormone (TSH) (median: 0.93 [0.007-2.9] µIU/mL), free T4 (1.3 [0.93-2.2] ng/dL), free T3 (3.0 [2.3-5.0] ng/dL), total T4 (9.9 [6.4-16.9] ng/dL), and total T3 (135 [88-231] ng/dL). If the nonpregnant reference range of serum TSH was used, eight women (4.8%) would be misclassified as having subclinical hyperthyroidism, and two women (1.2%) with subclinical hypothyroidism would be missed. In multivariate analysis, nulliparous (adjusted odds ratio [OR] from model 1-3: 2.02, 2.05, 2.02; 95% CI, 1.08-3.77, 1.10-3.81, 1.11-3.66; p = 0.027, 0.023, 0.022, respectively) and multivitamin nonusers (adjusted OR from model 1-3: 1.86, 1.85, 1.78; 95% CI, 1.04-3.34, 1.03-3.32, 1.004-3.71; p = 0.038, 0.039, 0.049, respectively) had increased odds of having lower UIC levels <150 µg/L. CONCLUSION: The iodine nutritional status in the first trimester is adequate in Taiwan; however, certain subgroups such as nulliparous and multivitamin nonusers are still at risk for iodine deficiency. Gestational thyroid function reference ranges are needed for correct diagnosis of thyroid dysfunction in pregnancy.

Reference intervals for thyroid function from the fifth to seventh day of life in twin-pregnancy preterm neonates: an 8-year retrospective study.

PURPOSE: The immature and developing hypothalamic-pituitary-thyroid axis leads to different levels of thyroid function in twin neonates, including free thyroxine (FT4), free triiodothyronine (FT3), and thyroid stimulating hormone (TSH) levels. No reference intervals for twins have been established until now. To compensate for this lack, we collected data and established this standard across different gestational ages (GAs) and sexes. METHODS: A total of 273 pairs of neonates admitted to the NICU in Southeast China from 2015 to 2022 were included. Each pair was divided into Neonate A (relatively heavy birth weight (BW)) and Neonate B (relatively light BW). Their thyroid functions were analyzed to establish reference intervals and comparisons were made stratified by GA and sex. RESULTS: The FT3, FT4, and TSH reference intervals in twin neonates with a GA of 26-36 weeks were as follows: Neonate A and B: 3.59 ± 0.99 and 3.57 ± 1.00 pmol/L; Neonate A and B: 17.03 ± 5.16 and 16.77 ± 5.29 pmol/L; and Neonate A and B: 4.097 ± 3.688 and 4.674 ± 4.850 mlU/L, respectively. There were significant differences between serum FT3 and FT4 reference intervals and GA (p < 0.05). The serum FT3 and FT4 reference intervals for male neonates were lower than those for female neonates in the 29-32-week group (p < 0.05). CONCLUSION: This was the first study, to our knowledge, to establish reference intervals for thyroid function in twin neonates from the fifth to seventh day of life, which will be beneficial for the diagnosis and management of congenital hypothyroidism.

The paradox of spring: Thyroid and glucocorticoid responses to cold temperatures and food availability in free living Carneddau ponies.

In seasonal environments, maintaining a constant body temperature poses challenges for endotherms. Cold winters at high latitudes, with limited food availability, create opposing demands on metabolism: upregulation preserves body temperature but depletes energy reserves. Examining endocrine profiles, such as thyroid hormone triiodothyronine (T3) and glucocorticoids (GCs), proxies for changes in metabolic rate and acute stressors, offer insights into physiological trade-offs. We evaluated how environmental conditions and gestation impact on faecal hormone metabolites (fT3Ms and fGCMs) from late winter to spring in a free-living population of Carneddau ponies. Faecal T3Ms were highest in late February and March, when temperatures were lowest. Then, fT3Ms concentrations decreased throughout April and were at the lowest in May before increasing towards the end of the study. The decline in fT3M levels in April and May was associated with warmer weather but poor food availability, diet diversity and diet composition. On the other hand, fGCM levels did not display a clear temporal pattern but were associated with reproductive status, where pregnant and lactating females had higher fGCM levels as compared to adult males and non-reproductive females. The temporal profile of fT3Ms levels highlights metabolic trade-offs in a changing environment. In contrast, the ephemeral but synchronous increase in fGCM concentrations across the population suggest a shared experience of acute stressors (i.e., weather, disturbance or social). This multi-biomarker approach can evaluate the role of acute stressors versus energy budgets in the context of interventions, reproduction, seasonality and environmental change, or across multiple scales from individuals to populations.