Treatment with levothyroxin in subclinical hypothyroidism is associated with increased mortality in the elderly

Hypothyroidism and metabolic cardiovascular disease

Cardiovascular disease (CVD) remains the leading cause of death worldwide, representing a major health issue of social and economic relevance. Both hyperthyroidism and hypothyroidism are very common in the adult population, and both disorders may contribute to the onset and progression of CVD. After a brief description of the role of thyroid hormones (THs) on the physiology of the cardiovascular system and the potential mechanism that links THs alterations with changes in cardiac function, blood pressure, endothelial function, and lipid levels, we review updated data about the clinical impact of overt hypothyroidism (OH) and subclinical hypothyroidism (SCH) on CV risk, CVD, and mortality. Furthermore, we summarize the current evidence for treating SCH with levothyroxine (L-T4). Several guidelines of distinguished endocrine societies recommend treatment for SCH with TSH higher than 10 mIU/L, where the benefit of L-T4 therapy is more evident for younger people, but still controversial in those aged over 65 years. Based on current knowledge, more research efforts are needed to better address the clinical management of CV risk and CVD in the elderly affected by SCH.

Cardiovascular and bone health outcomes in older people with subclinical hypothyroidism treated with levothyroxine: a systematic review and meta-analysis

BACKGROUND

Thyroid dysfunction is common in older people, with females at higher risk. Evidence suggests that thyroid-stimulating hormone (TSH) levels naturally increase with age. However, as uniform serum TSH reference ranges are applied across the adult lifespan, subclinical hypothyroidism (SCH) diagnosis is more likely in older people, with some individuals also being commenced treatment with levothyroxine (LT4). It is unclear whether LT4 treatment in older people with SCH is associated with adverse cardiovascular or bone health outcomes.

METHODS

A systematic review and meta-analysis were performed to synthesise previous studies evaluating cardiovascular and bone health outcomes in older people with SCH, comparing LT4 treatment with no treatment. PubMed, Embase, Cochrane Library, MEDLINE, and Web of Science databases were searched from inception until March 13, 2023, and studies that evaluated cardiovascular and bone health events in people with SCH over 50 years old were selected.

RESULTS

Six articles that recruited 3853 participants were found, ranging from 185 to 1642 participants, with the proportion of females ranging from 45 to 80%. The paucity of data resulted in analysis for those aged over 65 years only. Additionally, a study with 12,212 participants aged 18 years and older was identified; however, only data relevant to patients aged 65 years and older were considered for inclusion in the systematic review. Of these 7 studies, 4 assessed cardiovascular outcomes, 1 assessed bone health outcomes, and 2 assessed both. A meta-analysis of cardiovascular outcomes revealed a pooled hazard ratio of 0.89 (95% CI 0.71-1.12), indicating no significant difference in cardiovascular risk between older individuals with SCH treated with LT4 compared to those without treatment. Due to overlapping sub-studies, meta-analysis for bone health outcomes was not possible.

CONCLUSIONS

This systematic review and meta-analysis found no significant association between LT4 use and cardiovascular and bone health outcomes in SCH participants over 65 years.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42022308006.

Assessing the cardiovascular effects of levothyroxine use in an ageing United Kingdom population (ACEL-UK) protocol: a cohort and target trial emulation study

BACKGROUND

Subclinical hypothyroidism is diagnosed when serum thyroid stimulating hormone levels are higher whilst free thyroxine levels remain within their respective reference ranges. These reference ranges are uniformly applied in all adults, despite serum thyroid stimulating hormone levels naturally increasing with age. Research has found that mildly elevated thyroid stimulating hormone levels may be associated with some benefits in ageing patients, including reduced mortality and better cardiorespiratory fitness. Levothyroxine is typically prescribed to patients with hypothyroidism, but no conclusive evidence exists on whether levothyroxine therapy is beneficial or detrimental in older subclinical hypothyroid patients. Despite this, prescriptions for levothyroxine are increasing year-on-year. This study aims to determine if receiving levothyroxine affects the cardiovascular and bone health outcomes of subclinical patients in primary care aged 50 years and over.

METHODS

This project includes a retrospective cohort analysis and a target trial emulation study using electronic patient records collected between 2006 and 2021 and recorded in The Health Improvement Network database. The primary outcome of this study is to compare the cardiovascular outcomes of subclinical hypothyroid patients aged over 50 years treated with levothyroxine compared to those untreated. Secondary outcomes are bone health and all-cause mortality outcomes. Descriptive and inferential statistics will both be employed to analyse the data. Secondary analysis will explore confounding factors, including age, sex, smoking status, body mass index, co-morbidities, and levothyroxine dosage.

DISCUSSION

There needs to be a greater understanding of the potential risks of the current treatment for older patients with subclinical hypothyroidism in a primary care setting. We will investigate the clinical importance of this issue and whether older subclinical hypothyroid patients have poorer outcomes when treated. Clarifying this concern may help address the healthcare resource implications of ageing patients being misclassified as having mild hypothyroidism, as these patients are more likely to repeat their blood tests. This could reduce prescription wastage and improve patient outcomes and quality of life in the ageing population.

TRIAL REGISTRATION

Not applicable.

Management of thyroid dysfunction and thyroid nodules in the ageing patient

Thyroid dysfunction is a common endocrine disorder in the general population, with a reported prevalence of 10-15%. However, this rate is even higher in older adults, with an estimated prevalence of ≈25% in some populations. Since elderly patients usually present more comorbidities than younger individuals, thyroid dysfunction may carry a synergistic negative health impact, mainly due to increased cardiovascular disease risk. Moreover, thyroid dysfunction in the elderly can be more difficult to diagnose due to its subtle or even asymptomatic clinical presentation, and the interpretation of thyroid function tests may be affected by drugs that interfere with thyroid function or by the coexistence of several diseases. On the other hand, thyroid nodules are also a prevalent condition in older adults, and its incidence increases with age. The assessment and management of thyroid nodules in the ageing patient should take into account several factors, as risk stratification, thyroid cancer biology, patient´s overall health, comorbidities, treatment preferences, and goals of care. In this review article, we summarize the current knowledge on the pathophysiology, diagnosis, and therapeutic management of thyroid dysfunction in elderly patients and we also review how to identify and manage thyroid nodules in this population.

Age-Related Hormones Changes and Its Impact on Health Status and Lifespan

The increase in life expectancy is accompanied with an increased consultation of age-related pathologies including endocrine disorders. Two main areas are focusing the attention of medical and social research in older population: the diagnosis and care of this heterogeneous population, and the interventional measures potentially useful to mitigate age-related functional declines and to increase health and quality of lifespan. Thus, better understanding the physiopathology of aging and establishing accurate diagnostic and personalized approaches are a priority and currently an unmet need of the medical community. The endocrine system plays a major role in survival and lifespan through regulating vital processes such as energy consumption and optimizing the stress response among others. The aim of this paper is to review the physiological evolution of the main hormonal functions in aging and its clinical translation to improve our approach to the aging patient.

Treating hypothyroidism is not always easy: When to treat subclinical hypothyroidism, TSH goals in the elderly, and alternatives to levothyroxine monotherapy

The majority of patients with hypothyroidism feel better when levothyroxine treatment restores thyroid-stimulating hormone (TSH) concentrations to normal. Increasingly, a significant minority of patients remain symptomatic and are dissatisfied with their treatment. Overzealous treatment of symptomatic patients with subclinical hypothyroidism may contribute to dissatisfaction among hypothyroidism patients, as potential hypothyroid symptoms in patients with minimal hypothyroidism rarely respond to treatment. Thyroid hormone prescriptions have increased by 30% in the United States in the last decade. The diagnosis of subclinical hypothyroidism should be confirmed by repeat thyroid function tests ideally obtained at least 2 months later, as 62% of elevated TSH levels may revert to normal spontaneously. Generally, treatment is not necessary unless the TSH exceeds 7.0-10 mIU/L. In double-blinded randomized controlled trials, treatment does not improve symptoms or cognitive function if the TSH is less than 10 mIU/L. While cardiovascular events may be reduced in patients under age 65 with subclinical hypothyroidism who are treated with levothyroxine, treatment may be harmful in elderly patients with subclinical hypothyroidism. TSH goals are age dependent, with a 97.5 percentile (upper limit of normal) of 3.6 mIU/L for patients under age 40, and 7.5 mIU/L for patients over age 80. In some hypothyroid patients who are dissatisfied with treatment, especially those with a polymorphism in type 2 deiodinase, combined treatment with levothyroxine and liothyronine may be preferred.

Divergent prognostic effects of pre-existing and treatment-emergent thyroid dysfunction in patients treated with immune checkpoint inhibitors

Background

Thyroid dysfunction is among the most common autoimmune diseases and immune checkpoint inhibitor (ICI)-induced immune-related adverse events (irAE). We determined the association between longitudinal thyroid function and clinical outcomes in patients treated with ICI.

Methods

We identified all patients treated with ICI at UT Southwestern Medical Center from January 1, 2011, through December 31, 2020. We defined normal thyroid stimulating hormone (TSH) and free thyroxine (FT4) levels according to institutional reference range. We defined clinical thyroid dysfunction using established criteria incorporating labs and treatment. We determined the association between thyroid function and overall survival (OS) using Kaplan–Meier curves, log-rank tests, and multivariate Cox proportional hazards model.

Results

A total of 1781 patients were included in analyses, of whom 381 (21%) had abnormal baseline TSH. Patients with abnormal baseline TSH were more likely to be female, have kidney cancer, and initiate levothyroxine after ICI initiation (all P < 0.001). Patients with abnormal baseline TSH had inferior OS (median 16 vs 27 months; P < 0.001). Among patients with normal baseline TSH, those who had abnormal TSH after ICI initiation had improved OS (median 41 vs 22 months; P < 0.001). In a multivariate Cox model, abnormal baseline TSH was associated with worse OS (HR 1.62; 95% CI, 1.30–2.02; P < 0.001), while initiation of levothyroxine after ICI initiation was associated with improved OS (HR 0.62; 95% CI, 0.44–0.88; P = 0.008).

Conclusions

ICI-induced thyroid dysfunction is associated with improved survival, although abnormal TSH prior to ICI initiation is associated with inferior survival.

Precis

Thyroid abnormalities occur commonly in the general population and as immunotherapy toxicities. We found that immunotherapy-induced thyroid dysfunction is associated with better survival, but pre-existing thyroid abnormalities convey worse outcomes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00262-022-03151-2.

Effect of Levothyroxine on Older Patients With Subclinical Hypothyroidism: A Systematic Review and Meta-Analysis

BACKGROUND

Subclinical hypothyroidism (SCH) is usually treated with levothyroxine, but there is controversy as to whether SCH should be treated, especially for older patients. The aim of the systematic review and meta-analysis was to evaluate whether levothyroxine has a beneficial or harmful effect on older patients with SCH.

METHODS

Databases including PubMed, Embase, Cochrane Library, Web of Science, Wanfang, Weipu and China National Knowledge Infrastructure were searched from inception until December 21, 2021. Subjects must be diagnosed with SCH, and older than or equal to 60 years of age. Interventions should be thyroid hormone therapy (e.g. levothyroxine). The literature was independently screened by 2 researchers. Statistical analysis was performed using RevMan5.3 software.

RESULTS

A total of 13 articles were included. Meta-analysis results showed that in older SCH patients, levothyroxine can significantly reduce cholesterol (TC) (p < 0.00001), triglyceride (TG) (p < 0.00001), low-density lipoprotein cholesterol (LDL-C) (p = 0.03) and apolipoprotein B (ApoB) (p < 0.00001). In addition, levothyroxine had no significant effect on bone mineral density, fatigue, hypothyroidism symptoms, quality of life, BMI, cognitive function, depression, blood pressure, etc. in older SCH patients, and also did not significantly increase the incidence of adverse events.

CONCLUSIONS

Among older SCH patients, levothyroxine treatment may reduce TC, TG, LDL-C, and ApoB.

Cardiovascular outcomes and rates of fractures and falls among patients with brand-name versus generic L-thyroxine use

PURPOSE

To compare cardiovascular outcomes and rates of fractures and falls among patients with persistent brand-name versus generic L-thyroxine use.

METHODS

Retrospective, 1:1 propensity-matched longitudinal study using a national administrative claims database to examine adults (≥18 years) who initiated either brand or generic L-thyroxine between 2008 and 2018, censored at switch or discontinuation of L-thyroxine formulation or disenrollment from the health plan. Main outcome measures included rates of hospitalization for atrial fibrillation, myocardial infarction, congestive heart failure, stroke, spine and hip fractures, and rate of falls in the outpatient or inpatient setting. Hospitalizations for pneumonia were used as a negative control.

RESULTS

195,046 adults initiated treatment with L-thyroxine between 2008 and 2017: 87% generic and 13% brand formulations. They were mostly women (76%), young (94.6% under age 65), white (66%), and 47% had baseline thyroid stimulating hormone levels between 4.5 and 9.9 mIU/L. Among 35,667 propensity-matched patients, there were no significant differences between patients treated with brand versus generic L-thyroxine in atrial fibrillation (HR 0.96, 0.58-1.60), myocardial infarction (HR 0.66, 0.39-1.14), congestive heart failure (HR 1.30, 0.78-2.16), stroke (0.72, 0.49-1.06), spine (HR 0.87, 0.38-1.99) and hip fractures (HR 0.86, 0.26-2.82), or fall outcomes (HR 1.02, 0.14-7.32). Hospitalization rates for pneumonia (used as negative control) did not differ between groups (HR 0.85, 0.61-1.19). There were no interactions between brand versus generic L-thyroxine, these outcomes, and thyroid cancer, age, or L-thyroxine dose subgroups.

CONCLUSIONS

We found no significant differences in cardiovascular outcomes and rates of falls and fractures for patients who filled brand versus generic L-thyroxine.

Expert consensus on diagnosis and treatment for elderly with thyroid diseases in China (2021)

In order to improve the diagnosis and treatment of senile thyroid diseases in China and to promote healthy aging, the Endocrine Metabolic Diseases Group of the Chinese Geriatrics Society, and the Thyroid Group of the Chinese Society of Endocrinology jointly drafted the "Expert consensus on diagnosis and treatment for Chinese elderly with thyroid diseases" (referred to as consensus). The Consensus consists of five parts that set 40 recommendations on main clinical issues. The consensus emphasizes clinical focus on the age-related changes of the hypothalamus-pituitary-thyroid axis in the elderly, and it recommends application of comprehensive geriatric assessment to thoroughly evaluate the impact of thyroid diseases and relevant intervention on overall health condition. Meanwhile, it recommends generalization of screening for hypothyroidism during admission to nursing institution or hospital, and routine health check-ups. Furthermore, it develops individualized stratified management on hyperthyroidism, hypothyroidism, thyroid nodules, and differentiated thyroid carcinoma in the elderly distinguished from the youngers, including treatment regimen, control ranges, and flowcharts for diagnosis and treatment. The Consensus will provide the basis for clinical decisions and health management of thyroid diseases in the elderly by geriatrician, endocrinologist, and general practitioners.

Thyroid Hormone Supplementation and All-Cause Mortality in Community-Dwelling Older Adults: Results from the Baltimore Longitudinal Study of Aging

BACKGROUND

Although elevated thyrotropin (TSH) is common in older adults, controversy exists over what degree of elevation should be treated with thyroid hormone supplements. Isolated, elevated TSH in this population can be consistent with aging-related adaptations rather than indicative of primary thyroid disease, raising the possibility that thyroid hormone replacement may be harmful.

OBJECTIVES

Determine the association between all-cause mortality and levothyroxine use among older adults.

DESIGN

Longitudinal observational study.

SETTING

Baltimore Longitudinal Study of Aging.

PARTICIPANTS

One thousand two hundred and fifty eight community dwelling adult participants aged 65+ with an average of 9 years of follow up.

MEASUREMENTS

Thyroid and pituitary hormone levels and thyroid hormone supplementation were determined at each visit. Incident rate ratios (IRR) for all-cause mortality were calculated using time-dependent Poisson regression models to accommodate the varying start times. To isolate the effects of hormone replacement from its effects on TSH, the association between treatment and all-cause mortality was analyzed in participants with stable thyroid function status throughout follow-up (N = 638).

RESULTS

Thyroid hormone supplementation was not associated with a significant increase all-cause mortality in the subsequent year in the fully adjusted model (IRR = 1.40, 95% confidence interval (CI) = 0.93-2.12). In a stratified analysis of euthyroid participants, thyroid hormone use was associated with significantly greater mortality, with an adjusted IRR = 1.81 (95% CI = 1.10-2.98).

CONCLUSION

The increased mortality associated with thyroid hormone use among the subclass of euthyroid community dwelling older adults is consistent with a model in which TSH elevation can result from a variety of underlying pathophysiologic processes, not all of which should be treated with thyroid hormone supplementation. Clinicians should consider overall clinical status when interpreting an isolated elevated TSH in older adults.

Clinical Outcomes After Discontinuation of Thyroid Hormone Replacement: A Systematic Review and Meta-Analysis

Background: Levothyroxine (LT4) is one of the most commonly prescribed medications. Although considered a life-long replacement therapy, LT4 therapy can be discontinued for some patients. This study aims at: (i) reviewing the evidence on clinical outcomes of patients undergoing thyroid hormone replacement discontinuation, (ii) identifying the predictors of successful discontinuation, and (iii) systematically appraising frameworks used for deprescribing thyroid hormone. Methods: We searched multiple bibliographic databases, including Ovid MEDLINE(R) and Epub Ahead of Print, In-Process & Other Non-Indexed Citations and Daily, Ovid Embase, Ovid Cochrane Central Register of Controlled Trials, Ovid Cochrane Database of Systematic Reviews, and Scopus, from inception to February 2020 for studies in which thyroid hormone replacement was discontinued. Clinical outcomes assessed included: proportion of patients that remained euthyroid or needed to restart thyroid hormone replacement after discontinuation and frequency of clinical symptoms of hypothyroidism and adverse effects. We also evaluated predictors for discontinuation and deprescribing frameworks. Reviewers (F.J.K.T., N.B., N.M.S.O., S.M.) evaluated studies for inclusion, extracted data, and assessed methodological quality independently and in duplicate. Results: Seventeen observational studies at moderate to high risk of bias met inclusion criteria, including a total of 1103 patients (86% women) with an age range of 2-81 years. Approximately a third of patients undergoing thyroid hormone discontinuation remained euthyroid at follow-up (37.2%, 95% confidence interval [CI 24.2-50.1%], I² 97.5%). Subgroup analysis showed that patients with a previous diagnosis of overt hypothyroidism (OH) were less likely to remain euthyroid (11.8% [CI 0.4-23.2%], I² 90.3%) than patients with a prior diagnosis of subclinical hypothyroidism (SCH) (35.6% [CI 8.2-62.9%], I² 94.0%). No study followed a framework for systematically deprescribing LT4. Conclusions: Low-quality evidence suggests that up to a third of patients remained euthyroid after thyroid hormone discontinuation, with a higher proportion of patients with an initial diagnosis of SCH remaining euthyroid than patients with an initial diagnosis of OH. A deprescribing framework focusing on adequate selection of patients for deprescribing LT4 and a systematic process is warranted to guide clinicians in re-evaluating the need for LT4 in their patients.

The impact of subclinical hypothyroidism on long-term outcomes in older patients undergoing percutaneous coronary intervention

BACKGROUND

Subclinical hypothyroidism (SCH) is reportedly associated with an increased risk of adverse events in patients undergoing percutaneous coronary intervention (PCI). The prognostic significance of SCH in the elderly was poorly defined. The purpose of this study was to evaluate the association between SCH and long-term outcomes in older patients undergoing PCI.

METHODS

Three thousand one hundred sixty-eight patients aged 65 years or older who underwent PCI from January 2012 to October 2014 were included. Patients were divided into SCH group (n = 320) and euthyroidism (ET) group (n = 2848) based on thyroid function test. Cox proportional hazard regression analyses were used to estimate the relative risks (RRs) of all-cause death and cardiac death for patients with SCH during a 4-year follow-up period.

RESULTS

There were 227 deaths during the follow-up period including 124 deaths caused by cardiac events. There was no significant difference in mortality rate between the SCH group and the ET group (p > 0.05). After adjustment for covariates, compared with patients with ET, the RRs of death from all-cause and cardiac in patients with SCH were 1.261 (95%CI: 0.802-1.982, p = 0.315) and 1.231 (95%CI: 0.650-2.334, p = 0.524), respectively. When SCH was stratified by age, gender, and degree of thyroid-stimulating hormone elevation, no significant associations were also found in any stratum.

CONCLUSION

Our investigation revealed that SCH was negatively associated with the outcome of PCI in older patients.

Association of Thyroid Hormone Therapy with Mortality in Subclinical Hypothyroidism: A Systematic Review and Meta-Analysis

CONTEXT

Benefits of thyroid hormone therapy on mortality in adults with subclinical hypothyroidism remain undetermined.

OBJECTIVE

To summarize the impact of thyroid hormone therapy on mortality in adults with subclinical hypothyroidism.

DATA SOURCES

PubMed, Embase, Scopus, Web of Science, and Clinicaltrials.gov from inception until April 25, 2020.

STUDY SELECTION

Studies comparing the effect of thyroid hormone therapy with that of placebo or no therapy in adults with subclinical hypothyroidism on all-cause and/or cardiovascular mortality.

DATA EXTRACTION

Two reviewers independently extracted data and performed quality assessments. Random-effects models for meta-analyses were used.

DATA SYNTHESIS

Five observational studies and 2 randomized controlled trials with 21 055 adults were included. Overall, thyroid hormone therapy was not significantly associated with all-cause (pooled relative risk [RR] = 0.95, 95% confidence interval [CI]: 0.75-1.22, P = .704) or cardiovascular (pooled RR = 0.99, 95% CI: 0.82-1.20, P = .946) mortality. Subgroup analyses revealed that in younger adults (aged <65-70 years), thyroid hormone therapy was significantly associated with a lower all-cause (pooled RR = 0.50, 95% CI: 0.29-0.85, P = .011) and cardiovascular (pooled RR = 0.54, 95% CI: 0.37-0.80, P = .002) mortality. However, no significant association between thyroid hormone therapy and mortality was observed in older adults (aged ≥65-70 years).

CONCLUSIONS

Use of thyroid hormone therapy does not provide protective effects on mortality in older adults with subclinical hypothyroidism. However, thyroid hormone therapy for subclinical hypothyroidism may show benefits on morality in adults aged <65 to 70 years.

Hypothyroidism

Hypothyroidism is a common condition in which the thyroid gland provides insufficient amounts of thyroid hormone for the needs of peripheral tissues. The most common cause in adults is chronic lymphocytic thyroiditis (Hashimoto thyroiditis), but there are many other causes. Because most of the clinical features of hypothyroidism are nonspecific, the diagnosis requires laboratory testing. Serum thyroid-stimulating hormone (TSH) measurement is the best diagnostic test; an elevated TSH level almost always signals primary hypothyroidism. Serum free thyroxine levels may be below the reference range (overt hypothyroidism) or within the reference range (subclinical hypothyroidism). All patients with overt hypothyroidism should be treated, but those with subclinical hypothyroidism do not always benefit from treatment, especially elderly patients and those with baseline TSH levels below 10 mU/L. Oral L-thyroxine is the treatment of choice because of its well-demonstrated efficacy, safety, and ease of use. Therapy goals are symptom relief and maintenance of serum TSH levels within the reference range. Myxedema coma is a life-threatening form of decompensated hypothyroidism that must be treated with aggressive L-thyroxine replacement and other supportive measures in the inpatient setting.

TSH Levels in Subclinical Hypothyroidism in the 97.5th Percentile of the Population

The debate regarding the cutoff point in the treatment of patients with subclinical hypothyroidism (Shypo) is ongoing. Generally, two different groups are identified for treatment by levels of 10 and 20 mIU/L. Nevertheless, the question remains, "what cutoff point should be chosen?" We have written a selective nonsystematic review focused on the 97.5 percentile reference value reported in healthy subjects in a number of countries and observed important disparities, which partly show the challenge of identifying a single cutoff point for those patients needing medication. We identified studies of TSH on the natural history of subclinical hypothyroidism from population-based prospective cohort studies, which follow up patients for several years. The evolution of TSH levels in these patients is variable. Some cases of TSH may return to lower levels at different stages over the years, but others may not, possibly even developing into overt thyroid failure, also variable. We analyzed factors that may explain the normalization of serum TSH levels. In addition, we found that thorough population-based prospective cohort studies following up on TSH levels, thyroid antibodies, and ultrasonography are important in decisions made in the treatment of patients. However, the 97.5 percentile reference value varies in different countries; therefore, an international cutoff point for subclinical hypothyroidism cannot be recommended.

Aging Is Associated with Low Thyroid State and Organ-Specific Sensitivity to Thyroxine

Background: Serum thyroid state in older adults correlates with extended longevity. We hypothesized that age impacts not only systemic but also organ-specific thyroid state and response to thyroxine (T4). Methods: Young (3 months) and old (23 months) male mice were analyzed at baseline and after acute T4 challenge. Age effects on circulating thyrotropin (TSH) and thyroid hormone (TH) concentrations, transcript expression in the pituitary and thyroid were compared with organ-specific responses characterized by hepatic and cardiac content of TH and TH metabolites and expression of TH-target genes, as well as hepatic deiodinase 1 activity. Results: Circulating TH concentrations and hepatic and cardiac TH content were lower in old versus young mice. After injection with T4, conversion of T4 to triiodothyronine was decreased in old mice while TH transport in liver and heart was not affected. Organ-specific TH response was augmented in old mice in liver but not heart, indicating age- and tissue-specific sensitivity to TH. A compensatory increase of thyroid stimulating hormone subunit beta expression in the pituitary and increased serum TSH concentrations, but reduced expression of thyroid differentiation markers were found in old mice. Conclusions: We suggest that a reduced activity of the aged thyroid is responsible for the systemic low TH state in old mice. Further, divergent TH metabolism and tissue response in liver and heart occur after T4 treatment in an aged organism. These rodent data are in agreement with a much narrower window for T4 substitution in the older adults to avoid overtreatment.

Diagnosis and treatment of hypothyroidism in the elderly

The global population is aging with millions of people today living into their 90 s. Thyroid disease, particularly hypothyroidism, is widespread among all age groups, and it is expected to steadily increase as the population gets older. Clinical diagnosis of hypothyroidism is challenging, as the TSH reference range needs to be evaluated according to age, while evaluation of TSH levels must also take into account body weight and other variants such as polypharmacy, comorbidities, and general health condition. Since thyroid hormone has a potent regulatory effect on cholesterol metabolism, the possibility of thyroid dysfunction should be considered in cases of unexplained dyslipidemia. Once hypothyroidism has been confirmed, treatment requires caution, frequent cardiovascular monitoring, and individualized (precision) medicine. Treatment of subclinical hypothyroidism (SCH) in the elderly should be undertaken with care, guided by age and the degree of SCH: a TSH higher than 10 mU/l seems a reasonable threshold, though it should be regularly re-evaluated, while the LT4 dose needs to be tailored, taking into account the patient's health condition and the potential presence of dyslipidemia as well as other metabolic derangements.

Individualised requirements for optimum treatment of hypothyroidism: complex needs, limited options

Levothyroxine (LT4) therapy has a long history, a well-defined pharmacological profile and a favourable safety record in the alleviation of hypothyroidism. However, questions remain in defining the threshold for the requirement of treatment in patients with subclinical hypothyroidism, assessing the dose adequacy of the drug, and selecting the best treatment mode (LT4 monotherapy versus liothyronine [LT3]/LT4 combinations) for subpopulations with persisting complaints. Supplied as a prodrug, LT4 is enzymatically converted into the biologically more active thyroid hormone, triiodothyronine (T3). Importantly, tetraiodothyronine (T4) to T3 conversion efficiency may be impaired in patients receiving LT4, resulting in a loss of thyroid-stimulating hormone (TSH)-mediated feed-forward control of T3, alteration of the interlocking equilibria between serum concentrations of TSH, free thyroxine (FT4), and free triiodothyonine (FT3), and a decrease in FT3 to FT4 ratios. This downgrades the value of the TSH reference system derived in thyroid health for guiding the replacement dose in the treatment situation. Individualised conditionally defined setpoints may therefore provide appropriate biochemical targets to be clinically tested, together with a stronger focus on clinical presentation and future endpoint markers of tissue thyroid state. This cautionary note encompasses the use of aggregated statistical data from clinical trials which are not safely applicable to the individual level of patient care under these circumstances.

A Renewed Focus on the Association Between Thyroid Hormones and Lipid Metabolism

Thyroid dysfunction, manifesting as either overt or subclinical hypothyroidism, negatively affects lipid metabolism: this leads to hypercholesterolemia which progressively increases the risk for cardiovascular disease and, potentially, mortality. Hypercholesterolemia in hypothyroidism is mainly due to a reduction in low-density lipoprotein (LDL) receptor activity, this accompanied by concomitant diminishing control by triiodothyronine (T3) of sterol regulatory element-binding protein 2 (SREBP-2), which modulates cholesterol biosynthesis by regulating rate-limit degrading enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA) activity. Recently, 3,5-diiodothyronine (T2), a natural thyroid hormone derivative, was found to repress the transcription factor carbohydrate-response element-binding protein (ChREBP) and also to be involved in lipid catabolism and lipogenesis, though via a different pathway than that of T3. While thyroid hormone could therapeutically reverse the dyslipidemic profile commonly occurring in hypothyroidism, it should be borne in mind that the potency of the effects may be age-and sex-dependent. Thyroid hormone administration possibly also sustains and enhances the efficacy of hypolipidemic drugs, such as statins, ezetimibe and proprotein convertase subtilisin/kexin type 9 (PCSK9), in patients with dyslipidemia and hypothyroidism.