Circulating thyroid hormone levels in children

Association between polychlorinated biphenyl exposure and thyroid hormones: a systematic review and meta-analysis

Purpose: To conduct a comprehensive meta-analysis investigating the association between polychlorinated biphenyl (PCB) exposure and serum thyroid hormone levels among adults. Methods: Eleven studies met inclusion criteria for analysis following systematic search of PubMed, Embase, and Scopus databases. Of these, 7 studies measured exposure by the total sum of PCB congeners (∑PCB), 1 study measured individual PCB congener levels, and 3 studies measured both ∑PCB levels and PCB congener levels. Correlation coefficients (r) were extracted from each study. Summary estimates were calculated for ∑PCB levels and PCB congeners reported by 2 or more studies: PCB 28, 52, 101, 105, 118, 138, 153, and 180, using random effects model. Results: Significant negative correlation was found between ∑PCBs and T3 (r: -0.09; 95% CI: -0.17, -0.02) and FT3 (r: -0.24; 95% CI: -0.36, -0.12). Congener-specific analysis found T3 to be negatively correlated with PCB-153 (r: -0.19; 95% CI: -0.34, -0.03) and PCB-180 (r: -0.14; 95% CI: -0.26, -0.01), whereas TSH was positively correlated with PCB-105 (r: 0.15; 95% CI: 0.02, 0.28). Conclusions: The present study is the first meta-analysis to investigate the association between PCB exposure and thyroid hormone dysfunction among adults. Results suggest a significant association between PCB exposure and thyroid hormone dysregulation.

The associations of urinary DEHP metabolite levels, serum thyroid hormones, and thyroid-related genes among the adolescent students from China: a cross-sectional study

Our study aimed to investigate the associations between DEHP exposure and serum thyroid hormone levels in 347 adolescents and young adults. We measured DEHP metabolites including mono(2-ethylhexyl) phthalate (MEHP), mono(2-ethyl-5-oxohexyl) phthalate (MEOHP), mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono(2-ethyl-5-carboxypentyl) phthalate (MECPP), and mono(2-carboxymethyl)hexyl phthalate (MCMHP) in their urine. Total thyroxine (TT4), total triiodothyronine, free triiodothyronine, free thyroxine (FT4), thyroid-stimulating hormone and the mRNA levels of thyroid peroxidase (TPO), thyroglobulin (TG), sodium iodide symporter (NIS), thyroid transcription factor 1 (TTF-1), and paired box gene 8 (PAX-8) in serum were measured. The results of statistical analysis showed that urinary DEHP metabolites were generally negatively associated with TT4 levels in serum. In the males, the FT4 levels showed positive associations with urinary MEHP, MECPP, MCMHP, and ∑DEHP. The mRNA level of TG was significantly positively correlated with the levels of MECPP, MCMHP, and ∑DEHP, while the levels of TTF-1 and PAX-8 mRNA were significantly positively correlated with the levels of DEHP metabolites. Taken together, DEHP may affect the synthesis of TG by altering the normal transcription of TTF-1 and PAX-8, leading to decreased TT4 levels in Chinese adolescents.

Applications for non-invasive thyroid hormone measurements in mammalian ecology, growth, and maintenance

Thyroid hormones (THs) play a pivotal role in the regulation of metabolic activity throughout all life stages. Cross-talk with other hormone systems permits THs to coordinate metabolic changes as well as modifications in growth and maintenance in response to changing environmental conditions. The scope of this review is to explain the relevant basics of TH endocrinology, highlight pertinent topics that have been investigated so far, and offer guidance on measuring THs in non-invasively collected matrices. The first part of the review provides an overview of TH biochemistry, which is necessary to understand and interpret the findings of existing studies and to apply non-invasive TH monitoring. The second part focuses on the role of THs in mammalian ecology, and the third part highlights the role of THs in growth and maintenance. The fourth part deals with the advantages and difficulties of measuring THs in non-invasively collected samples. This review concludes with a summary that considers future directions in the study of THs.

Thyroid hormones and changes in body weight and metabolic parameters in response to weight loss diets: the POUNDS LOST trial

BACKGROUND

The role of thyroid hormones in diet-induced weight loss and subsequent weight regain is largely unknown.

OBJECTIVES

To examine the associations between thyroid hormones and changes in body weight and resting metabolic rate (RMR) in a diet-induced weight loss setting.

SUBJECTS/METHODS

Data analysis was conducted among 569 overweight and obese participants aged 30-70 years with normal thyroid function participating in the 2-year Prevention of Obesity Using Novel Dietary Strategies (POUNDS) LOST randomized clinical trial. Changes in body weight and RMR were assessed during the 2-year intervention. Thyroid hormones (free triiodothyronine (T3), free thyroxine (T4), total T3, total T4 and thyroid-stimulating hormone (TSH)), anthropometric measurements and biochemical parameters were assessed at baseline, 6 months and 24 months.

RESULTS

Participants lost an average of 6.6 kg of body weight during the first 6 months and subsequently regained an average of 2.7 kg of body weight over the remaining period from 6 to 24 months. Baseline free T3 and total T3 were positively associated, whereas free T4 was inversely associated, with baseline body weight, body mass index and RMR. Total T4 and TSH were not associated with these parameters. Higher baseline free T3 and free T4 levels were significantly associated with a greater weight loss during the first 6 months (P<0.05) after multivariate adjustments including dietary intervention groups and baseline body weight. Comparing extreme tertiles, the multivariate-adjusted weight loss±s.e. was -3.87±0.9 vs -5.39±0.9 kg for free T3 (P_trend=0.02) and -4.09±0.9 vs -5.88±0.9 kg for free T4 (P_trend=0.004). The thyroid hormones did not predict weight regain in 6-24 months. A similar pattern of associations was also observed between baseline thyroid hormones and changes in RMR. In addition, changes in free T3 and total T3 levels were positively associated with changes in body weight, RMR, body fat mass, blood pressure, glucose, insulin, triglycerides and leptin at 6 months and 24 months (all P<0.05).

CONCLUSIONS

In this diet-induced weight loss setting, higher baseline free T3 and free T4 predicted more weight loss, but not weight regain among overweight and obese adults with normal thyroid function. These findings reveal a novel role of thyroid hormones in body weight regulation and may help identify individuals more responsive to weight loss diets.

Effects of high di(2-ethylhexyl) phthalate (DEHP) exposure due to tainted food intake on pre-pubertal growth characteristics in a Taiwanese population

On May 23, 2011, a major scandal involving the illegal use of phthalates as clouding agents in food products was reported. Specifically, di(2-ethylhexyl) phthalate (DEHP) was purposefully added to foods as a substitute emulsifier. The purpose of this study was to examine the effects of DEHP exposure on the growth characteristics of the child victims of this scandal. Eighty-eight victims, originating from northern, central, and southern Taiwan and ranging in age from 6.0 to 10.5 years, were invited to participate in this study during clinic visits. The participants underwent follow-up health examinations from August 2012 to February 2013. We collected information on each participant's history of exposure to tainted food products using a questionnaire, and we analyzed their urinary concentrations of DEHP metabolites using high-performance liquid chromatography/tandem mass spectrometry. These data were then used to estimate their daily DEHP intake (DIAll) during the scandal. We also measured physical development parameters (height, weight, and bone age) and hormone levels (thyroid, sex and growth hormones) to evaluate their overall growth characteristics. The average (SD) duration of DEHP intake from tainted nutrition supplements was 1.39 (1.01) years. The median DIAll values were 19.93 and 20.69μg/kg bw/day for boys and girls, respectively. Among the enrolled children, the DIAll values of 46.9% of boys and 51.3% of girls exceeded the reference dose (RfD) of 20μg/kg bw/day established by the US Environmental Protection Agency. Our results demonstrate that DIAll is negatively associated with the height percentile, weight percentile, bone age/chronological age, and insulin-like growth factor 1 (IGF-1) levels but not with IGF binding protein 3 (IGF-BP3) level, IGF-1/IGF-BP3, sex hormones, or thyroid hormone levels. The DEHP DIAll value exceeded the RfD at high rates among children of both genders. Our results suggest that high levels of DEHP exposure due to the consumption of tainted food products are negatively associated with body weight, height, bone age, and IGF-1 levels in children. The likelihood of delayed puberty among the affected children is therefore a reasonable concern, and further follow-up is required.

Thyroid hormone levels in obese children and adolescents with non-alcoholic fatty liver disease

OBJECTIVE

We aimed to determine the association of thyroid functions with the components of metabolic syndrome (MS) and non-alcoholic fatty liver disease (NAFLD) in pediatric obese patients.

METHODS

The study included 109 obese children (aged 9-15 years) and a control group of 44 healthy age and gender-matched children of normal weight. NAFLD was diagnosed by conventional ultrasound examination. We assessed the anthropometric data and serum biochemical parameters including lipid profile, alanine aminotransferase (ALT), fasting glucose and insulin levels and thyroid stimulating hormone (TSH), free thyroxine (fT4) and free triiodothyronine (fT3) levels. The homeostasis model assessment of insulin resistance (HOMA-IR) was calculated as a measure of IR.

RESULTS

The mean age and gender distributions in the groups were similar (p=0.23). The mean body mass index (BMI) z-scores of obese children with grade 2-3 NAFLD were significantly higher than those of the obese children without hepatic steatosis (p<0.001). Mean ALT, triglyceride (TG) and LDL cholesterol increased and HDL-cholesterol significantly decreased as the hepatic steatosis increased (p<0.05). HOMA-IR levels in obese subjects with grade 2-3 NAFLD were significantly higher than those in both obese children without NAFLD and grade 1 NADFL (p=0.05 and 0.001, respectively). In the obese subjects, TSH levels were increased significantly as the degree of steatosis increased (p=0.04) but fT3 and fT4 levels were not different. In correlation analysis, TSH was significantly correlated with ALT, BMI SDS and the degree of steatosis.

CONCLUSIONS

Obese children demonstrate an increase in TSH levels as the degree of steatosis increased.

Thyroid hormone concentrations in relation to age, sex, pregnancy, and perinatal loss in bottlenose dolphins (Tursiops truncatus)

This study evaluated circulating concentrations of thyroid hormones in relation to age, sex, pregnancy status, and perinatal loss in bottlenose dolphins (Tursiops truncatus) under human care. A total of 373 blood samples were collected from 60 individual dolphins housed at nine aquariums/oceanariums. Serum concentrations of total and free thyroxine (T4) and triiodothyronine (T3) were analyzed with commercial RIA kits validated for use with dolphins. While the effect of age was indicated by higher (P<0.0001) concentrations of total and free T4 and T3 in juveniles than adults, the effect of sex on thyroid hormones was inconclusive. The effect of pregnancy was indicated by higher (P<0.035) total and free T4 and T3 during early pregnancy compared to non-pregnancy. For both successful and unsuccessful pregnancy outcomes, maternal concentrations of thyroid hormones were highest during early, intermediate during mid, and lowest during late pregnancy (P<0.07 to P<0.0001). Compared to live and thriving births, concentrations of total and free T4 and total T3 were lower (P<0.08 to P<0.001) in dolphins with perinatal loss. Lower concentrations ranged from 10% to 14% during early, 11% to 18% during mid, and 23% to 37% during late pregnancy. In conclusion, the effects of age, reproductive status and stage of pregnancy on thyroid hormone concentrations are necessary factors to take into account when assessing thyroid gland function. Since perinatal loss may be associated with hypothyroidism in dolphins, analysis of serum T4 and T3 should be considered for those dolphins that have a history of pregnancy loss.

Thyroid disrupting chemicals in plastic additives and thyroid health

The globally escalating thyroid nodule incidence rates may be only partially ascribed to better diagnostics, allowing for the assessment of environmental risk factors on thyroid disease. Endocrine disruptors or thyroid-disrupting chemicals (TDC) like bisphenol A, phthalates, and polybrominated diphenyl ethers are widely used as plastic additives in consumer products. This comprehensive review studied the magnitude and uncertainty of TDC exposures and their effects on thyroid hormones for sensitive subpopulation groups like pregnant women, infants, and children. Our findings qualitatively suggest the mixed, significant (α = 0.05) TDC associations with natural thyroid hormones (positive or negative sign). Future studies should undertake systematic meta-analyses to elucidate pooled TDC effect estimates on thyroid health indicators and outcomes.

Relationship between urinary phthalate and bisphenol A concentrations and serum thyroid measures in U.S. adults and adolescents from the National Health and Nutrition Examination Survey (NHANES) 2007-2008

BACKGROUND

Limited animal, in vitro, and human studies have reported that exposure to phthalates or bisphenol A (BPA) may affect thyroid signaling.

OBJECTIVE

We explored the cross-sectional relationship between urinary concentrations of metabolites of di(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), and BPA with a panel of serum thyroid measures among a representative sample of U.S. adults and adolescents.

METHODS

We analyzed data on urinary biomarkers of exposure to phthalates and BPA, serum thyroid measures, and important covariates from 1,346 adults (ages ≥ 20 years) and 329 adolescents (ages 12-19 years) from the National Health and Nutrition Examination Survey (NHANES) 2007-2008 using multivariable linear regression.

RESULTS

Among adults, we observed significant inverse relationships between urinary DEHP metabolites and total thyroxine (T4), free T4, total triiodothyronine (T3), and thyroglobulin, and positive relationships with thyroid-stimulating hormone (TSH). The strongest and most consistent relationships involved total T4, where adjusted regression coefficients for quintiles of oxidative DEHP metabolites displayed monotonic dose-dependent decreases in total T4 (p-value for trend < 0.0001). Suggestive inverse relationships between urinary BPA and total T4 and TSH were also observed. Conversely, among adolescents, we observed significant positive relationships between DEHP metabolites and total T3. Mono(3-carboxypropyl) phthalate, a secondary metabolite of both DBP and di-n-octyl phthalate, was associated with several thyroid measures in both age groups, whereas other DBP metabolites were not associated with thyroid measures.

CONCLUSIONS

These results support previous reports of associations between phthalates-and possibly BPA--and altered thyroid hormones. More detailed studies are needed to determine the temporal relationships and potential clinical and public health implications of these associations.

Induction of a hypothyroid state during juvenile development delays pubertal reactivation of the neuroendocrine system governing luteinising hormone secretion in the male rhesus monkey (Macaca mulatta)

The present study aimed to determine the influence of thyroid status on the timing of the pubertal resurgence in gonadotrophin-releasing hormone pulse generator activity [tracked by circulating luteinising hormone (LH) levels] in male rhesus monkeys. Six juvenile monkeys were orchidectomised and then treated with the antithyroid drug, methimazole, from 15-19 months until 36 months of age, at which time thyroxine (T(4)) replacement was initiated. Four additional agonadal monkeys served as controls. Blood samples were drawn weekly for hormonal assessments. Body weight, crown-rump length and bone age were monitored at regular intervals. By 8 weeks of methimazole treatment, plasma T(4) had fallen sharply, and the decline was associated with a plasma thyroid-stimulating hormone increase. In controls, plasma LH levels remained undetectable until the pubertal rise occurred at 29.3 +/- 0.2 months of age. This developmental event occurred in only half of the methimazole-treated animals before 36 months of age when T(4) replacement was initiated. The hypothyroid state was associated with a profound arrest of growth and bone maturation, but increased body mass indices and plasma leptin levels. T(4) replacement in methimazole-treated monkeys was associated with the pubertal rise in LH in the remaining three animals and accelerated somatic development in all six animals. Although pubertal resurgence in LH secretion occurred at a later chronological age in methimazole-treated animals compared to controls, bone age, crown-rump length and body weight at that time did not differ between groups. There were no long-term differences in plasma prolactin between groups. We conclude that juvenile hypothyroidism in male primates causes a marked delay in the pubertal resurgence of LH secretion, probably occasioned at the hypothalamic level. Whether this effect is meditated by an action of thyroid hormone directly on the hypothalamus or indirectly as a result of the concomitant deficit in somatic development remains to be determined.

Age-related changes in serum free thyroxine during childhood and adolescence

The purposes of this study were to reevaluate age-related changes in the concentration of serum free thyroxine (T4) between early infancy and adulthood, and to study the relationship of serum thyrotropin to these changes in free T4. Five hundred thirty-six healthy infants, children, adolescents, and adults between 1 day and 45 years of age were studied. Serum free T4 was determined by direct equilibrium dialysis, thyrotropin by a sensitive immunoassay, and total T4 by radioimmunoassay. Free T4 concentrations were age dependent and differed significantly (p < 0.001) at 1 to 4 days, 2 to 20 weeks, 5 to 24 months, 2 to 7 years, 8 to 20 years, and 21 to 45 years of age. Corresponding free T4 concentrations (mean +/- SEM) were 48.1 +/- 1.5, 20.3 +/- 0.6, 17.0 +/- 0.4, 19.9 +/- 0.4, and 21.2 +/- 0.4 pmol/L (3.74 +/- 0.12, 1.58 +/- 0.05, 1.32 +/- 0.03, 1.55 +/- 0.03, 1.32 +/- 0.03, and 1.65 +/- 0.03 ng/dl), respectively. Age-related reference ranges were determined. Changes in the relationship between serum thyrotropin and free T4 were complex, indicating age-related changes in pituitary thyroid regulation. No correlation existed between concentrations of free T4 and total T4 after the first 13 days of life (r2 < 0.01). We conclude that (1) pediatric free T4 concentrations and free T4-thyrotropin relationships differ from those in adults and (2) age-related changes in total T4 do not indicate age-related changes in either free T4 or thyroid function, after 13 days of age.

Management of patients with congenital hypothyroidism

The biochemical state and treatment of 73 children and 44 adults up to the age of 40 with proved congenital hypothyroidism were assessed in a regional study in the north of England. The findings showed that a substantial proportion of the patients were having inappropriate treatment or were not taking their treatment regularly and that in some of these there were clinical effects.

Primary hypothyroidism and the low T3 syndrome in thalassaemia major

Basal thyroid function was assessed from the serum thyroxine, triiodothyronine, and thyroid-stimulating hormone concentrations in 114 patients (mean age 13·6 years), designated group 1, with thalassaemia major. Forty of these patients were further evaluated (group 2) for serum-free thyroxine, and free and reverse triiodothyronine concentrations. The response of thyroid-stimulating hormone to thyrotrophin-releasing hormone was measured in 25 patients from this subgroup. Results were compared with those from 53 control subjects. Primary hypothyroidism, defined by a raised thyroid-stimulating hormone level above the upper range limit of 6·5 μIU/ml of the controls, was present in 17·5% of the 114 patients. In group 2 patients, a spectrum of thyroid disease spanning uncompensated and compensated primary hypothyroidism and decreased thyroid reserve was evident. The presence of primary hypothyroidism (uncompensated and compensated) was associated with an age of at least 10 years, an increased incidence of iron toxicity-related systemic complications, and an increased transfusion iron load, but not with an increased serum ferritin level. In the total 114 patients there were 9 who had the low triiodothyronine (sick euthyroid) syndrome. Primary hypothyroidism occurs in a significant proportion of thalassaemia major patients in the absence of obvious clinical signs of hypothyroidism; the low triiodothyronine syndrome associated with non-thyroidal disease is not uncommon.

Hypothyroidism and growth failure in diabetes mellitus

The prevalence of thyroid disease in 134 children, adolescents, and young adults with diabetes mellitus beginning in childhood is described. Clustering of a family history of thyroid disease and the presence of thyrogastric antibodies in some patients supports the concept of familial autoimmunity. In 4 children a diagnosis of hypothyroidism had already been made, one of whom had shown marked faltering of growth. In a further 3 there was evidence of previously unrecognised subclinical hypothyroidism but the growth of 2 of them had been good. The findings of this study indicate that while subclinical hypothyroidism should be considered in a diabetic whose growth is faltering, it is rarely a cause of such growth failure.

Goitre and hypothyroidism in the newborn after cutaneous absorption of iodine

Iodine goitre and hypothyroidism in 5 newborn infants in an intensive care unit were induced by cutaneous absorption of iodine, after numerous skin applications of iodine alcohol. The infant's skin permeability allows severe iodine overloading of the thyroid, resulting in goitre and hypothyroidism. Ioduria should always be sought in a newborn infant showing hypothyroidism. Iodine should not be used as a skin disinfectant in young infants.