Seasonal variation in thyroid size in healthy males

Seasonal variations in levels of human thyroid-stimulating hormone and thyroid hormones: a meta-analysis

Seasonal dynamics in biological functions of mammals is regulated by melatonin-mediated circannual fluctuations in the secretion of thyroid-stimulating hormone (TSH) and thyroid hormones. Most anatomical and molecular structures responsive to photoperiod and melatonin secretion changes and the associated receptors are preserved in modern humans. This work aimed to determine the seasonal dynamics of TSH and thyroid hormone levels (total triiodothyronine (T3), free triiodothyronine (FT3), thyroxine (T4), free thyroxine (FT4) and to investigate the dependence of these variations on gender, age and amplitude of meteorological fluctuations. A meta-analysis of 13 panel and 7 cross-sectional studies was performed using Review Manager 5.3 (Cochrane Library). We found that circulating TSH levels were higher in winter than in other seasons, and FT4 levels were higher in autumn than in winter. T4 level had no pronounced seasonal dynamics. The level of circulating T3 was significantly higher in winter than in summer and FT3 levels were lower in summer than in autumn and spring. In addition, analysis of TSH seasonal dynamics (winter vs summer) accounting for gender differences showed pronounced increases in TSH levels during winter in women, but not in men; and also significant increases in FT4 levels during summer in men, but not in women. Seasonal dynamics of FT3 and T4 did not depend on gender. Seasonal dynamics of TSH did not change with respect to age. We also found that the extent of the seasonal dynamics of TSH is influenced by the extent of the annual dynamics of the partial density of oxygen in the air, as well as the magnitude of the annual dynamic of meteorological factors that determine it (atmospheric pressure and relative humidity).

SCREENED: A Multistage Model of Thyroid Gland Function for Screening Endocrine-Disrupting Chemicals in a Biologically Sex-Specific Manner

Endocrine disruptors (EDs) are chemicals that contribute to health problems by interfering with the physiological production and target effects of hormones, with proven impacts on a number of endocrine systems including the thyroid gland. Exposure to EDs has also been associated with impairment of the reproductive system and incidence in occurrence of obesity, type 2 diabetes, and cardiovascular diseases during ageing. SCREENED aims at developing in vitro assays based on rodent and human thyroid cells organized in three different three-dimensional (3D) constructs. Due to different levels of anatomical complexity, each of these constructs has the potential to increasingly mimic the structure and function of the native thyroid gland, ultimately achieving relevant features of its 3D organization including: 1) a 3D organoid based on stem cell-derived thyrocytes, 2) a 3D organoid based on a decellularized thyroid lobe stromal matrix repopulated with stem cell-derived thyrocytes, and 3) a bioprinted organoid based on stem cell-derived thyrocytes able to mimic the spatial and geometrical features of a native thyroid gland. These 3D constructs will be hosted in a modular microbioreactor equipped with innovative sensing technology and enabling precise control of cell culture conditions. New superparamagnetic biocompatible and biomimetic particles will be used to produce "magnetic cells" to support precise spatiotemporal homing of the cells in the 3D decellularized and bioprinted constructs. Finally, these 3D constructs will be used to screen the effect of EDs on the thyroid function in a unique biological sex-specific manner. Their performance will be assessed individually, in comparison with each other, and against in vivo studies. The resulting 3D assays are expected to yield responses to low doses of different EDs, with sensitivity and specificity higher than that of classical 2D in vitro assays and animal models. Supporting the "Adverse Outcome Pathway" concept, proteogenomic analysis and biological computational modelling of the underlying mode of action of the tested EDs will be pursued to gain a mechanistic understanding of the chain of events from exposure to adverse toxic effects on thyroid function. For future uptake, SCREENED will engage discussion with relevant stakeholder groups, including regulatory bodies and industry, to ensure that the assays will fit with purposes of ED safety assessment. In this project review, we will briefly discuss the current state of the art in cellular assays of EDs and how our project aims at further advancing the field of cellular assays for EDs interfering with the thyroid gland.

Seasonal Changes in Serum Thyrotropin Concentrations Observed from Big Data Obtained During Six Consecutive Years from 2010 to 2015 at a Single Hospital in Japan

BACKGROUND

This study analyzed big data for serum thyrotropin (TSH), free triiodothyronine (fT3), and free thyroxine (fT4) concentrations in patients who had attended the outpatient clinic of Ito Hospital (Tokyo, Japan) during a recent six-year period (between January 1, 2010, and December 31, 2015) in order to investigate for seasonal changes.

METHODS

The serum TSH concentrations were reviewed for all 135,417 patients aged >20 years. Patients with any thyroid diseases were included, irrespective of whether they were receiving drug therapy. In total 1,637,721 serum samples were analyzed for TSH, 1,626,269 for fT3, and 1,669,381 for fT4.

RESULTS

It was observed that the TSH concentrations showed annual changes during the six-year period. They decreased during the summer, while they increased during the winter. The TSH concentrations were negatively correlated with the daily temperatures (Spearman rank correlation coefficient -0.4486; p < 0.0001). The same applied for the correlation between fT3 concentrations and daily temperatures.

CONCLUSIONS

The fact that the TSH concentrations show annual changes in areas where the temperature ranges during the year are rather wide should be borne in mind for interpretation of results.

Circadian and Circannual Rhythms in Thyroid Hormones: Determining the TSH and Free T4 Reference Intervals Based Upon Time of Day, Age, and Sex

BACKGROUND

Establishing the reference interval for thyrotropin (TSH) and free thyroxine (T4) is clinically important because a number of disease states have been linked to alterations in TSH and free T4 concentrations that are within the 95% confidence interval for normal thyroid hormone values. Age, sex, time of day, and ethnicity are known to affect circulating levels of TSH and free T4 but have not been used to establish reference intervals. The purpose of this study was to define the reference interval for TSH and free T4 taking into account age, sex, ethnicity, and circadian and circannual variability.

METHODS

We performed a retrospective analysis of 465,593 TSH and 112,994 free T4 measurements from subjects ages 1-104 years with no thyroid disease using a single TSH and free T4 immunoassay method. Boundaries for the central 95% of patient values, taking into account hour of day, day of year, sex, and age were calculated.

RESULTS

Females had significantly higher TSH and free T4 levels than males; the magnitude of these differences did not exceed 0.1 mIU/L or 0.1 ng/dL respectively. Although the 2.5% TSH reference interval remains constant through the day, date, and age ranges, the upper limit (97.5%) of the TSH reference interval increases from 6.45 to 7.55 mIU/L with age, due primarily to a progressive increase in the amplitude of the nocturnal TSH surge. Additionally, significant ethnic differences in TSH circadian periodicity occur between African American, Pacific Island, and Caucasian populations.

CONCLUSIONS

The reference interval for TSH varies significantly by age, sex, hour of day, and ethnicity. Time of year does not affect the TSH reference interval, and age, sex, hour of day and time of year do not affect the free T4 reference interval.

Seasonal variation of neonatal transient hyperthyrotropinemia in Tehran province, 1998-2005

Seasonal aggregation and the monthly rate of neonatal transient hyperthyrotropinemia (THT) were assessed. From November 1998 to April 2005, neonates of gestational age ≥37 wks, birth weight 2500-4000 g, birth length 45-55 cm, and 1st min Apgar score >3, who had thyrotropin (TSH) ≥20 mU/L in their cord dried-blood specimen, but without congenital hypothyroidism, were enrolled in the study. The recall rate equals the rate of THT occurrence in this study. Of 47,945 neonates, 555 had THT (recall rate: 1.2%). The aggregated seasonal recall rate (recall for further assessment to rule out congenital hypothyroidism) was significantly higher in winter (January, February, and March) than the other seasons (p < .0001). Winter had higher recall rate in each year as compared to other seasons, but the overall rate of recalls decreased in 2001 and 2002. Excluding the first 6 months (due to erratic variations), the remaining 72 months revealed a relatively sinusoidal pattern in monthly recall rates; indeed, there was an initial 11-month high recall rates (1.7%), followed by a 33-month decrease (0.7%), a 19-month increase (1.9%), and a final 9-month decrease (0.8%). The recall rate of each of these time intervals was significantly different from that of the next time interval (p < .0001). The monthly recall rates were best fitted to cubic curve estimation and then autoregressive integrated moving average (ARIMA) (0, 1, 1) models. THT occurs significantly more in winter than in other seasons, and this suggests a possible role for time-varying factor(s) contributing to its seasonal preponderance.

Assessing the bioequivalence of analogues of endogenous substances ('endogenous drugs'): considerations to optimize study design

BACKGROUND

Assessment of the bioequivalence of generic versions of certain reference drugs is complicated by the presence of endogenous levels of said compounds which cannot be distinguished from externally derived compound levels following drug administration. If unaccounted for, the presence of endogenous compound biases towards equivalence in bioequivalence studies of these drugs. Bioequivalence assessments may be complicated further as disposition of the exogenous analogue can be subject to various endogenous processes resulting in nonlinear pharmacokinetics. To overcome these inherent biases a number of different strategies have been employed.

AIMS

To critically review methods used to overcome confounding biases in bioequivalence studies of 'endogenous' drugs.

METHODS

A literature search of the EMBASE and PubMed databases was performed.

RESULTS

The following strategies were identified: ablation/modulation of baseline endogenous substance levels; recruitment of 'substance-deficient' populations; restriction of dietary intake of the relevant substance; standardization of conditions with the potential to affect relevant homeostatic mechanisms; correction for baseline substance levels; and administration of supra-therapeutic drug doses.

CONCLUSIONS

On the basis of this review key study design concepts, intended to optimize the design of future bioequivalence studies of these so-called 'endogenous drugs', are described. The dual stable isotope method, which could be used in a specific context, is also discussed.

Assessment of Levothyroxine Sodium Bioavailability

BACKGROUND

Assessment of dosage form performance in delivering endogenous compounds, such as hormones, in vivo requires a specific approach.

OBJECTIVES

Assessment of relative bioavailability of levothyroxine sodium (L-T4) from eight solid preparations, compared with a liquid formulation, by using pharmacological doses, and critical evaluation of trial methodology based on the pooled analysis of individual data.

DESIGN

Eight open-label, randomised, single-dose, crossover phase I studies using eight solid L-T4 dosage forms (25, 50, 75, 100, 125, 150, 175, 200 microg per tablet; administered total doses 600, 625 or 700 microg) and a liquid formulation; assessment of relative bioavailability by 90% confidence intervals for the relative area under the concentration-time curve (AUC) of total thyroxine (TT4), i.e. protein-bound plus free thyroxine, calculated by using the recommended log AUC four-way analysis of variance models for crossover designs. For the pooled analysis, general linear models were applied to assess the validity of model assumptions, to identify potential sources of effect modification, to discuss alternative modelling approaches with respect to endogenous hormone secretion and to give recommendations for future designs and sample sizes.

PARTICIPANTS

One hundred and sixty-nine healthy males; 29 of these individuals participating in two studies.

INTERVENTIONS

Single oral doses of L-T4 tablets and the liquid formulation administered after fasting, separated by at least 6 weeks; a total of 396 drug exposures.

MAIN OUTCOME MEASURES

TT4 AUC from 0 to 48 hours and peak plasma concentration with and without baseline correction.

RESULTS

Each study demonstrated equivalence of the tablets to the drinking solution, independent of the chosen analysis model. Sequence effects that could devalidate the chosen crossover approach were not found. Period effects with changing directions that could best be explained by seasonal variation were detected. While the pre-specified method of baseline correction of simply subtracting individual time-zero TT4 values was disadvantageous, the analysis of total AUC could be improved considerably by covariate adjustment for baseline TT4. With this approach, sample sizes could have been substantially reduced or, alternatively, the recommended equivalence ranges could be reduced to +/-6%.

CONCLUSION

Using a single pharmacological dose of L-T4 in two-period crossover designs is a safe and reliable procedure to assess L-T4 dosage form performance. With an adequate statistical modelling approach, the design is efficient and allows general conclusions with moderate sample sizes.

Acclimation of a non-indigenous sub-Arctic population: seasonal variation in thyroid function in interior Alaska

Total, as well as free, T4 and T3 levels were obtained over four seasons for young male infantry soldiers assigned to interior Alaska. Significant seasonal variations were found in both T3 and T4. Total T4 and T3 levels were highest in winter, while free T4 and T3 levels were highest in early spring. Correlations with melatonin levels from a concurrent study showed an association between late day (17.00) mean spot melatonin levels during the preceding summer and T3 levels in winter and spring. Differences in seasonal T4 and T3 levels between indigenous and newly arrived people in the sub-Arctic may be related not only to cold acclimation but also to light.

Thyroid disease in pustulosis palmoplantaris

An increased frequency of thyroid autoantibodies has been reported in patients with palmar and plantar pustulosis (PPP). This study was undertaken to determine the frequency and type of thyroid disease in 32 patients with this disease compared with a control group. Thyroid disease was demonstrated in 53% of the patients with PPP as compared to 16% in the matched control group. Fourteen patients with PPP had an enlarged thyroid and in six there were thyroid autoantibodies. There appears to be an increased incidence of goitre and thyroid autoantibodies in PPP with a decrease in the level of the thyroid hormones.