Effects of Altering Levothyroxine Dose on Energy Expenditure and Body Composition in Subjects Treated With LT4

Are resting metabolic rate and clinical symptoms affected by variation of serum thyroid stimulating hormone levels within the normal range in healthy and women with hypothyroidism? A case-control study

BACKGROUND

It is unclear whether variation in thyroid stimulating hormone (TSH) levels within the reference range affect energy expenditure and clinical symptoms and even within the normal range of TSH levels, resting energy expenditure may alter. The aim of the present study was to determine whether treated hypothyroid subjects and healthy subjects with a low-normal TSH range (0.3-2.3 mIU/L) have better clinical outcomes and increased energy expenditure than those with a high-normal TSH range (2.3-4.3 mIU/L).

METHODS

This was a case-control study of 160 overweight/obese women with TSH levels across the reference range of 0.3-4.3 mU/l. Subjects were paired in four groups: healthy subjects with low-normal target TSH (n = 40), healthy subjects with high-normal target TSH (n = 40), subjects with treated hypothyroidism with low-normal target TSH (n = 40), and subjects with treated hypothyroidism with high-normal target TSH (n = 40). Resting energy expenditure (RMR), dietary intake, body composition, physical activity, and biochemical markers were assessed.

RESULTS

Subjects with low-normal (≤2.3 mU/L) and high-normal (>2.3 mU/L) TSH levels did not differ in terms of RMR, serum T3 levels, and clinical symptoms except fatigue (P = 0.013). However, serum fT4 levels were found to be significantly different between the study groups (P = 0.002). Serum fT4 concentration was the highest in subjects with treated hypothyroidism with low-normal target TSH.

CONCLUSION

Variation in serum TSH levels within the reference range did not significantly affect REE and clinical symptoms except fatigue in healthy and women with hypothyroidism.

Critical Approach to Hypothyroid Patients With Persistent Symptoms

Hypothyroidism is a common condition, and numerous studies have been published over the last decade to assess the potential risks associated with this disorder when inappropriately treated. The standard of care for treatment of hypothyroidism remains levothyroxine (LT4) at doses to achieve biochemical and clinical euthyroidism. However, about 15% of hypothyroid patients experience residual hypothyroid symptoms. Some population-based studies and international population-based surveys have confirmed dissatisfaction with LT4 treatment in some hypothyroid patients. It is well established that hypothyroid patients treated with LT4 exhibit higher serum thyroxine:triiodothyronine ratios and can have a persistent increase in cardiovascular risk factors. Moreover, variants in deiodinases and thyroid hormone transporter genes have been associated with subnormal T3 concentrations, persistent symptoms in LT4-treated patients, and improvement in response to the addition of liothyronine to LT4 therapy. The American (ATA) and European Thyroid Association (ETA) guidelines have recently evolved in their recognition of the potential limitations of LT4. This shift is reflected in prescribing patterns: Physicians' use of combination therapy is prevalent and possibly increasing. Randomized clinical trials have recently been published and, while they have found no improvement in treating hypothyroid patients, a number of important limitations did not allow generalizability. Meta-analyses have reported a preference rate for combination therapy in 46.2% hypothyroid patients treated with LT4. To promote discussions about an optimal study design, the ATA, ETA, and British Thyroid Association have recently published a consensus document. Our study provides a useful counterpoint on the controversial benefits of treating hypothyroid patients with combination therapy.

Serum Thyrotropin and Triiodothyronine Levels in Levothyroxine-treated Patients

CONTEXT

Small adjustments in levothyroxine (LT4) dose do not appear to provide clinical benefit despite changes in thyrotropin (TSH) levels within the reference range. We hypothesize that the accompanying changes in serum total triiodothyronine (T3) levels do not reflect the magnitude of the changes in serum TSH.

OBJECTIVE

This work aims to characterize the relationships of serum free thyroxine (FT4) vs T3, FT4 vs TSH, and FT4 vs the T3/FT4 ratio.

METHODS

This cross-sectional, observational study comprised 9850 participants aged 18 years and older treated with LT4 from a large clinical database from January 1, 2009, to December 31, 2019. Patients had been treated with LT4, subdivided by serum FT4 level. Main outcome measures included model fitting of the relationships between serum FT4 vs TSH, FT4 vs T3, and FT4 vs T3/FT4. Mean and median values of TSH, T3, and T3/FT4 were calculated.

RESULTS

The relationships T3 vs FT4 and TSH vs FT4 were both complex and best represented by distinct, segmented regression models. Increasing FT4 levels were linearly associated with T3 levels until an inflection point at an FT4 level of 0.7 ng/dL, after which a flattening of the slope was observed following a convex quadratic curve. In contrast, increasing FT4 levels were associated with steep declines in TSH following 2 negative sigmoid curves. The FT4 vs T3/FT4 relationship was fit to an asymptotic regression curve supporting less T4 to T3 activation at higher FT4 levels.

CONCLUSION

In LT4-treated patients, the relationships between serum FT4 vs TSH and FT4 vs T3 across a range of FT4 levels are disproportionate. As a result, dose changes in LT4 that robustly modify serum FT4 and TSH values may only minimally affect serum T3 levels and result in no significant clinical benefit.

In silico dose adjustment of levothyroxine after total thyroidectomy using fuzzy logic methodology: A proof-of-concept study

Thyroid hormone replacement therapy is used to raise undesirably low concentrations of natural thyroid hormones, commonly by administrating levothyroxine (LT4). Finding the appropriate LT4 dose regime, particularly for patients undergone thyroidectomy, is still demanding more effort, and much research has been conducted. Providing a new fuzzy logic system, a useful control algorithm, we aim to introduce a proper LT4 dosing regimen for every thyroidectomized patient in a computerized environment. Consequently, we contrast the differences between our proposed dose regime and conventional monotherapy methods using THYROSIM, a thyroid simulation application. Considering our nine defined comparative criteria, results reveal that the FLS dose regime is dominant in terms of six indexes, while the discrepancies are not noticeable in the other three indexes. A great superiority of FLS dose regime is its ability to reduce the time to reach desirable thyrotropin (Thyroid Stimulating Hormone, TSH) serum concentration to 6 days post-thyroidectomy, and keep the T4, T3, and TSH values in the normal window afterward. The proposed FLS could be an applicable decision support system for physicians as they can define their intended Individual Target Value of TSH for each patient to optimize LT4 dose adjustment.

The Influence of Levothyroxine on Body Composition and Physical Performance in Subclinical Hypothyroidism

Levothyroxine is commonly used to treat hypothyroidism. This study investigates how far the intake of L-T4 influences body composition, energy expenditure, respiratory quotient as well as strength, endurance and mobility in premenopausal women who suffer from subclinical hypothyroidism. Twenty-five women (27.36±5.77 years) with subclinical hypothyroidism were included in the study. The intake of levothyroxine was assumed. Subjects were examined immediately after study inclusion, after two months of levothyroxine use, and after TSH was fully adjusted to the reference range. In all measurements TSH, fT3 and fT4 were determined, body weight, body composition, energy expenditure and the respiratory quotient were measured, and a test battery was performed to identify strength, mobility and endurance capacity. TSH decreased from 5.95±0.99 μIU/ml at study inclusion to 1.2±0.33 μIU/ml after final trial. No change in weight, BMI, muscle mass, fat mass, energy expenditure and respiratory quotient was observed (p>0.05). A significant improvement in chest press (p=0.002), leg extension (p<0.001), right-hand grip strength (p=0.009) shoulder mobility (p<0.001), hip mobility (p=0.07), explosive strength (p=0.041) and the anaerobic threshold (p=0.13) was identified. Likewise, a non-significant (p=0.298) increase in left-hand grip strength could be detected.In summary, although levothyroxine does not positively affect body composition, energy expenditure and respiratory quotient, it can improve strength, mobility and endurance performance. For this reason, treatment with levothyroxine is recommended to improve exercise capacity in subclinical hypothyroidism.

Higher thyroid hormone has a negative association with lower limb lean body mass in euthyroid older adults: Analysis from the Baltimore Longitudinal study of aging

Background: Hyperthyroidism is associated with lower lean body mass, as a result of catabolic actions of thyroid hormone. Therefore, higher thyroid hormone levels could be a factor in the development of sarcopenia and age associated functional decline. The relationship between thyroid hormone and muscle mass in ambulatory, euthyroid older adults is not known. Method: We used mixed-effects models to estimate the cross-sectional relationships (accounting for inter-person variability) between thyroid axis hormone measures and lower limb composition or sarcopenia at visits in the Baltimore Longitudinal Study of Aging (BLSA) at which DEXA scans were available and both thyrotropin (TSH) and free thyroxine (FT4) were in the reference range. Analyses were adjusted for levothyroxine use, age, race, sex, BMI, smoking, alcohol intake, cholesterol, and systolic blood pressure. Results: 1442 euthyroid participants (median age 68, 50% female, and 69% white) contributed to 5306 visits from 2003 to 2019. FT4 was negatively associated with lower limb lean mass (beta: 88.49; 95% Confidence Interval (CI): 122.78, -54.20; p < 0.001) and positively associated with sarcopenia (OR: 1.11%, 95% CI: 1.01, 1.22) in the whole cohort. Additionally, higher FT4 was associated with lower leg lean mass (beta: 66.79; 95% CI: 102.24, -31.33; p < 0.001) and sarcopenia (OR:1.09%, 95% CI:1.01, 1.18) in older adults, but not in younger adults alone. Conclusion: In euthyroid older adults, higher FT4 is associated with lower leg lean mass and higher odds of sarcopenia. Understanding the relationship between thyroid hormone and sarcopenia is needed to improve clinical decision-making and avoid functional decline from excess thyroid hormone use in older adults.

Restoration of euthyroidism with levothyroxine: implications of etiology of hypothyroidism and the degree of residual endogenous thyroid function

There are many thyroid-related factors that combine with non-thyroid-related factors in order to affect the patient response to treatment of hypothyroidism, in terms of their satisfaction with therapy. Some of the thyroid-derived factors include the etiology of the hypothyroidism and the amount of residual thyroid function that the patient retains. These two factors may be intertwined and affected by a third influence, the presence of thyroid peroxidase antibodies. The downstream consequences of the interactions between these three factors may influence both free thyroxine and free triiodothyronine levels, TSH concentrations, and various thyroid biomarkers. Evidence of the widespread importance of thyroid hormones can be inferred from the multiple genes that are regulated, with their regulation affecting multiple serum biomarkers. Thyroid biomarkers may extend from various well-known serum markers such as lipids and sex hormone-binding globulin to serum levels of thyroid hormone metabolites. Moreover, the interplay between thyroid hormones and biomarkers and their relative ratios may be different depending on the hypothyroidism etiology and degree of residual thyroid function. The ultimate significance of these relationships and their effect on determining patient-reported outcomes, quality of life, and patient satisfaction is, as yet, poorly understood. However, identification of better biomarkers of thyroid function would advance the field. These biomarkers could be studied and correlated with patient-reported outcomes in future prospective studies comparing the impact of various thyroid hormone therapies.

Optimal Thyroid Hormone Replacement

Hypothyroidism is a common endocrinopathy, and levothyroxine is frequently prescribed. Despite the basic tenets of initiating and adjusting levothyroxine being agreed on, there are many nuances and complexities to consistently maintaining euthyroidism. Understanding the impact of patient weight and residual thyroid function on initial levothyroxine dosage and consideration of age, comorbidities, thyrotropin goal, life stage, and quality of life as levothyroxine is adjusted can be challenging and continually evolving. Because levothyroxine is a lifelong medication, it is important to avoid risks from periods of overtreatment or undertreatment. For the subset of patients not restored to baseline health with levothyroxine, causes arising from all aspects of the patient's life (coexistent medical conditions, stressors, lifestyle, psychosocial factors) should be broadly considered. If such factors do not appear to be contributing, and biochemical euthyroidism has been successfully maintained, there may be benefit to a trial of combination therapy with levothyroxine and liothyronine. This is not supported by the majority of randomized clinical trials, but may be supported by other studies providing lower-quality evidence and by animal studies. Given this discrepancy, it is important that any trial of combination therapy be continued only as long as a patient benefit is being enjoyed. Monitoring for adverse effects, particularly in older or frail individuals, is necessary and combination therapy should not be used during pregnancy. A sustained-release liothyronine preparation has completed phase 1 testing and may soon be available for better designed and powered studies assessing whether combination therapy provides superior therapy for hypothyroidism.

Patients with rare endocrine conditions have corresponding views on unmet needs in clinical research

PURPOSE

European Reference Network on Rare Endocrine Conditions' (Endo-ERN) mission is to reduce and ultimately abolish inequalities in care for patients with rare endocrine conditions in Europe. This study assesses which themes related to rare endocrine conditions are prioritized by patients for clinical research.

METHODS

A survey was developed, translated into 22 different European languages, and distributed to patients with rare endocrine conditions. Patients were asked to give priority scores to listed prespecified topics: fertility, heritability, tiredness, daily medicine intake, sleep quality, physical discomfort, and ability to work, partake in social life, and sports. They were also asked to suggest further important areas for research in open fields.

RESULTS

After data cleaning, 1378 survey responses were analyzed. Most responses were received from Northern (47%) and Western Europeans (39%), while Southern (11%) and Eastern Europe (2%) were underrepresented. Respondents were most interested in research concerning ability to participate in social life and work. Patients suggested key areas to work: long-term side effects of medical treatments and quality of life. Some priorities differed between disease groups, both for prespecified and open topics and reflected aspects of patients' individual conditions.

CONCLUSIONS

With this large survey, Endo-ERN gained insight into patients' unmet needs in scientific research. Patients prioritized research on ability to work and participation in social activities, though needs differ between the disease groups. Clinical experts should incorporate the results of this survey into the design of future studies on rare endocrine conditions. We aim to utilize these results in designing patient-reported outcome measures for the disease areas covered by Endo-ERN.

Weight Gain After Thyroidectomy: A Systematic Review and Meta-Analysis

CONTEXT

Weight gain is a major driver of dissatisfaction and decreased quality of life in patients with hypothyroidism. Data on the changes in body weight following thyroidectomy are conflicting.

OBJECTIVE

To perform a systematic review of the literature and a meta-analysis of weight changes following total thyroidectomy.

DATA SOURCES

Literature search on PubMed.

STUDY SELECTION

Studies in English published between September 1998 and May 2018 reporting post-thyroidectomy weight changes.

DATA EXTRACTION

Data were reviewed and compared by 3 investigators; discrepancies were resolved by consensus. Meta-analyses were performed using fixed and random effect models. Univariable and multivariable meta-regression models for weight change were implemented against study follow-up, gender, and age. Exploratory subgroup analyses were performed for indication for surgery.

DATA SYNTHESIS

Seventeen studies (3164 patients) with 23.8 ± 23.6 months follow-up were included. Severe heterogeneity across studies was observed. Using a random effect model, the estimated overall weight change was a gain of 2.13 kg, 95% confidence interval (CI; 0.95, 3.30). Age was negatively associated with weight change (β = -0.238, P < 0.001). In subgroup analyses, weight gain was more evident in patients undergoing thyroidectomy for hyperthyroidism: 5.19 kg, 95% CI (3.21, 7.17) vs goiter or malignancy 1.55 kg, 95% CI (0.82, 2.27) and 1.30 kg, 95% CI (0.45, 2.15), respectively.

CONCLUSIONS

Patients undergoing thyroidectomy experience possible mild weight gain, particularly younger individuals and those with hyperthyroidism as the indication for surgery. Prospective studies directed to assess the pathophysiology of weight gain post-thyroidectomy, and to test novel treatment modalities, are needed to better characterize post-thyroidectomy weight changes.

Levothyroxine Replacement in Obese Adults: The Role of Metabolic Variables and Aging on Thyroid Testing Abnormalities

CONTEXT

General rates of over- and underreplacement in levothyroxine (LT4) users with primary hypothyroidism are variably high. No information on LT4 adequacy exists in obesity.

OBJECTIVE

We explored rates and factors relating to LT4 adequacy in obese patients with primary hypothyroidism.

SETTING

Tertiary care center.

DESIGN

Among 4954 consecutive obese patients admitted between 2011 and 2014, 691 hypothyroid patients receiving LT4 therapy and 691 body mass index (BMI)-, age-, and sex-matched euthyroid controls underwent analysis of thyroid function, glucolipid profile, body composition, and indirect calorimetry. LT4 users were classified into low TSH (<0.27 mU/L), euthyroid (0.27 to 4.2 mU/L), and high TSH (>4.2 mU/L).

RESULTS

LT4 users constituted 13.9% of the incident population. TSH was low in 7.5%, high in 17.2%, and normal in 75.2% of LT4 users. Overtreatment decreased with aging and more LT4 users ≥65 years of age had normal TSH than those <65 years of age (P < 0.05). Compared with the euthyroid obese group, LT4 users showed higher adiposity, similar insulin resistance, but a healthier lipid profile. In multivariable analyses, LT4 dose was predicted by fat-free mass, hypothyroidism cause, and sex (P < 0.0001 to < 0.05). Risk of LT4 overreplacement increased with younger age (OR 0.96; 95% CI 0.94 to 0.99), higher LT4 dose (OR 2.98; 95% CI 1.44 to 6.14), and lower BMI (OR 0.93; 95% CI 0.88 to 0.99). Male sex increased the likelihood of LT4 underreplacement (OR 2.37; 95% CI 1.10 to 5.11).

CONCLUSIONS

Obesity is associated with milder rates of inadequate LT4 treatment compared with nonobese populations. LT4 adequacy increases with aging. Age, body composition, and sex are main determinants of LT4 requirements in obesity.

T4 + T3 combination therapy: any progress?

Guidelines on T4 + T3 combination therapy were published in 2012. This review investigates whether the issue is better understood 7 years later. Dissatisfaction with the outcome of T4 monotherapy remains high. Persistent symptoms consist mostly of fatigue, weight gain, problems with memory and thinking and mood disturbances. T4 monotherapy is associated with low serum T3 levels, which often require TSH-suppressive doses of L-T4 for normalization. Peripheral tissue thyroid function tests during T4 treatment indicate mild hyperthyroidism at TSH < 0.03 mU/L and mild hypothyroidism at TSH 0.3-5.0 mU/L; tissues are closest to euthyroidism at TSH 0.03-0.3 mU/L. This is explained by the finding that whereas T4 is usually ubiquinated and targeted for proteasomal degradation, hypothalamic T4 is rather stable and less sensitive to ubiquination. A normal serum TSH consequently does not necessarily indicate a euthyroid state. Persistent symptoms in L-T4 treated patients despite a normal serum TSH remain incompletely understood. One hypothesis is that a SNP (Thr92Ala) in DIO2 (required for local production of T3 out of T4) interferes with its kinetics and/or action, resulting in a local hypothyroid state in the brain. Effective treatment of persistent symptoms has not yet realized. One may try T4 + T3 combination treatment in selected patients as an experimental n = 1 study. The 2012 ETA guidelines are still valid for this purpose. More well-designed randomized clinical trials in selected patients are key in order to make progress. In the meantime the whole issue has become rather complicated by commercial and political overtones, as evident from skyrocketing prices of T3 tablets, aggressive pressure groups and motions in the House of Lords.

Subclinical Hypothyroidism: A Review

IMPORTANCE

Subclinical hypothyroidism, defined as an elevated serum thyrotropin (often referred to as thyroid-stimulating hormone, or TSH) level with normal levels of free thyroxine (FT4) affects up to 10% of the adult population.

OBSERVATIONS

Subclinical hypothyroidism is most often caused by autoimmune (Hashimoto) thyroiditis. However, serum thyrotropin levels rise as people without thyroid disease age; serum thyrotropin concentrations may surpass the upper limit of the traditional reference range of 4 to 5 mU/L among elderly patients. This phenomenon has likely led to an overestimation of the true prevalence of subclinical hypothyroidism in persons older than 70 years. In patients who have circulating thyroid peroxidase antibodies, there is a greater risk of progression from subclinical to overt hypothyroidism. Subclinical hypothyroidism may be associated with an increased risk of heart failure, coronary artery disease events, and mortality from coronary heart disease. In addition, middle-aged patients with subclinical hypothyroidism may have cognitive impairment, nonspecific symptoms such as fatigue, and altered mood. In the absence of large randomized trials showing benefit from levothyroxine therapy, the rationale for treatment is based on the potential for decreasing the risk of adverse cardiovascular events and the possibility of preventing progression to overt hypothyroidism. However, levothyroxine therapy may be associated with iatrogenic thyrotoxicosis, especially in elderly patients, and there is no evidence that it is beneficial in persons aged 65 years or older.

CONCLUSIONS AND RELEVANCE

Subclinical hypothyroidism is common and most individuals can be observed without treatment. Treatment might be indicated for patients with subclinical hypothyroidism and serum thyrotropin levels of 10 mU/L or higher or for young and middle-aged individuals with subclinical hypothyroidism and symptoms consistent with mild hypothyroidism.

Reference intervals in the diagnosis of thyroid dysfunction: treating patients not numbers

Although assigning a diagnosis of thyroid dysfunction appears quite simple, this is often not the case. Issues that make it unclear whether thyroid function is normal include transient changes in thyroid parameters, inter-individual and intra-individual differences in thyroid parameters, age-related differences, and ethnic variations. In addition, a statistically calculated distribution of thyroid analytes does not necessarily coincide with intervals or cutoffs that have predictive value for beneficial or adverse health outcomes. Based on current clincial trial data, it is unclear which individuals with mild thyroid-stimulating hormone elevations will benefit from levothyroxine treatment. For example, only a small number of patients with thyroid-stimulating hormone values of more than 10 mIU/L have been studied in a randomised manner. Even if therapy is initiated for abnormal thyroid function, not all treated individuals are maintained at the desired treatment target, and therefore might still be at risk. The consequence of this is that each patient's thyroid function needs to be assessed on an individual basis with the entire clinical picture in mind. Monitoring also needs to be vigilant, and the targets for treatment reassessed continually.

Thyroid Hormone Action and Energy Expenditure

Energy metabolism is one of the most recognized targets of thyroid hormone action, which indeed plays a critical role in modulating energy expenditure in all of its components. This is because thyroid hormone receptors are ubiquitous, and thyroid hormones interact and influence most metabolic pathways in virtually all systems throughout the entire life of the organism. The pleiotropic actions of thyroid hormone are the results of interaction between the local availability of T3 and the signal transduction machinery, which confer in physiologic conditions time and tissue specificity of the hormonal signal despite negligible variations in circulating levels. Historically, the measurement of energy expenditure has been used as the gold standard for the clinical assessment of the hormonal action until the advent of the immunoassays for TSH and thyroid hormone, which have since been used as proxy for measurement of thyroid hormone action. Although the clinical correlates between thyroid hormone action and energy expenditure in cases of extreme dysfunction (florid hyperthyroidism or hypothyroidism) are well recognized, there is still controversy on the effects of moderate, subclinical thyroid dysfunction on energy expenditure and, ultimately, on body weight trajectory. Moreover, little information is available on the effects of thyroid hormone replacement therapy on energy expenditure. This mini review is aimed to define the clinical relevance of thyroid hormone action in normal physiology and functional disorders, as well the effects of thyroid hormone therapy on energy expenditure and the effects of changes in energy status on the thyroid hormone axis.

Can We Link Thyroid Status, Energy Expenditure, and Body Composition to Management of Subclinical Thyroid Dysfunction?

We discuss the study of Samuels et al., focusing on the effect that levothyroxine treatment has on energy expenditure and body composition in subclinical hypothyroidism.