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thyroid

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aliasesthyroid gland

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Thyroid

The thyroid gland is the largest endocrine gland in the neck, producing thyroxine (T4) and triiodothyronine (T3) — the primary regulators of metabolic rate, thermogenesis, cardiac output, bone turnover, and neurological development — as well as calcitonin, a calciotropic hormone produced by parafollicular cells. Thyroid hormone acts on virtually every tissue in the body, making thyroid dysfunction one of the most systemically consequential endocrine failures of aging.

Thyroid disease is among the most prevalent endocrinopathies in older adults: subclinical and overt hypothyroidism together affect an estimated 5–10% of the general adult population, with rates rising substantially past age 65. The most common etiology is Hashimoto thyroiditis, an organ-specific autoimmune disease whose incidence is amplified by the age-related dysregulation of immune surveillance — a direct interface with the disabled-adaptive-immunity hallmark. Understanding how the thyroid ages is clinically important because (a) age confounds standard TSH reference ranges, leading to potential overdiagnosis in healthy elderly, and (b) the largest RCT to date (TRUST, Stott 2017) found no symptomatic benefit from treating subclinical hypothyroidism in older adults — a result that challenges common clinical practice.

Anatomy and cell types

The adult thyroid weighs approximately 20–30 g and consists of two lobes connected by an isthmus, lying anterior to the trachea just below the larynx. Thyroid volume increases modestly with age, particularly in iodine-replete populations with nodular changes 1.

Follicular cells (thyrocytes)

Thyroid-follicular-cells (also called thyrocytes) are polarized epithelial cells arranged in spherical follicles surrounding a colloid lumen. They are the predominant cell type (~85% of thyroid mass) and are responsible for thyroid hormone biosynthesis via the following sequence:

  1. Iodide uptake — via sodium/iodide symporter (NIS) at the basolateral membrane, driven by the sodium gradient
  2. Thyroglobulin (Tg) synthesis — Tg is the ~660 kDa prohormone secreted into the follicle lumen
  3. Iodination (organification) — thyroid peroxidase (TPO) oxidizes iodide (via H₂O₂ generated by DUOX2) and incorporates it into tyrosine residues on Tg → monoiodotyrosine (MIT) and diiodotyrosine (DIT)
  4. Coupling — TPO couples MIT + DIT → T3 (3,5,3’-triiodothyronine) and DIT + DIT → T4 (thyroxine), covalently incorporated into Tg
  5. Secretion — TSH stimulation triggers endocytosis of Tg from the colloid lumen; lysosomes cleave T4/T3 from Tg; T4 (~80% of output) and T3 (~20%) are secreted into the circulation
  6. Peripheral conversion — most circulating T3 (~80%) is generated by 5’-deiodinase activity in peripheral tissues (liver, kidney, muscle) converting T4 → T3; this step is the rate-limiting bottleneck for active hormone delivery

Parafollicular cells (C cells)

Parafollicular-cells (C cells) are neuroendocrine cells scattered between follicles or at their periphery, deriving from the neural crest. They produce calcitonin, which inhibits osteoclast activity and lowers serum calcium. C cells are the cell of origin for medullary thyroid carcinoma (MTC). Their contribution to calcium homeostasis is minor compared to PTH and vitamin D in adults, but calcitonin has clinical relevance as a tumor marker and as a pharmacological agent for Paget disease.

The HPT axis

Thyroid hormone output is regulated by the hypothalamic-pituitary-thyroid (HPT) axis:

  • Hypothalamus → thyrotropin-releasing hormone (TRH) → pituitary
  • Anterior pituitary → thyroid-stimulating hormone (TSH) → thyroid follicular cells
  • Thyroid → T4/T3 → negative feedback at both pituitary and hypothalamus

TSH binds the TSH receptor (TSHR) on thyrocytes, activating cAMP/PKA signaling, which upregulates NIS expression, Tg synthesis, TPO activity, iodination, and T4/T3 secretion. Free T4 and free T3 (not protein-bound) are the biologically active fractions. In the systemic circulation, ~99.97% of T4 and ~99.7% of T3 are bound to thyroxine-binding globulin (TBG), transthyretin, and albumin.

Aging changes

1. TSH set-point rises with age

Population studies consistently demonstrate that median serum TSH levels increase with advancing age 2. In a community-based cohort of 3,885 men aged 70–89 years, the 2.5th–97.5th centile reference interval for TSH was 0.64–5.9 mIU/L — substantially wider and shifted upward relative to the conventional adult reference range of 0.4–4.0 mIU/L 3. Applying age-specific reference ranges to this cohort reclassified approximately 8% of men — identifying cases of previously unrecognized overt thyroid disease and subclinical hyperthyroidism that had been masked.

The mechanistic basis for rising TSH with age is incompletely understood but likely involves: (a) altered pituitary feedback sensitivity (decreased responsiveness to circulating T4); (b) reduced thyroid reserve (lower T4 output per unit TSH stimulus); (c) age-associated changes in TSH glycosylation that affect its bioactivity vs immunoreactivity (TSH isoforms measured by immunoassay may not reflect full biological potency); and (d) in some individuals, early subclinical autoimmune thyroid damage 4.

Clinical implication: Using a conventional TSH cutoff of 4.0 mIU/L to diagnose subclinical hypothyroidism in a 75-year-old likely overestimates the prevalence of pathological hypothyroidism in older adults. Many individuals in the 4–7 mIU/L range may represent a normal age-adjusted setpoint — particularly those who are asymptomatic.

2. Prevalence of subclinical and overt hypothyroidism

The NHANES III population study (n=17,353 US adults, 1988–1994) reported overall prevalence of subclinical hypothyroidism at 4.3% (TSH >4.5, normal free T4) and overt hypothyroidism at 0.3%, with rates significantly higher in women and older age groups 5. Anti-TPO antibodies were positive in 11.3% of the total sample, rising substantially with age, particularly in women.

In adults over 65, prevalence estimates from diverse cohorts range from 5–15% for subclinical hypothyroidism and approximately 2–5% for overt hypothyroidism 67. Variation across studies reflects differences in TSH cutoff definitions, iodine intake, sex distribution, and whether age-specific reference ranges are applied.

3. Reduced T4→T3 peripheral conversion

Aging is associated with a measurable decline in peripheral conversion of T4 to the more potent T3, mediated by reduced 5’-deiodinase (particularly type 1 deiodinase, DIO1) activity in target tissues 8. This produces a lower circulating T3/T4 ratio in older adults. Selenium deficiency — common in the elderly — impairs DIO1 activity (selenium is a cofactor of deiodinase enzymes), potentially amplifying the conversion deficit 8.

Practical consequence: even with a normal or high-normal serum TSH and normal free T4, older adults may have lower intracellular T3 availability than young adults with identical TSH values, contributing to a subclinical tissue hypothyroid state that evades standard biochemical detection. needs-replication — the clinical significance of reduced T3/T4 ratio in the absence of TSH elevation has not been established in large prospective human cohorts.

4. Non-thyroidal illness (low T3 syndrome)

Acute and chronic illness, surgery, and nutritional insufficiency suppress peripheral T4→T3 conversion and reduce total T3 without altering the HPT axis at its thyroid-output level 9. This “non-thyroidal illness syndrome” (NTIS, also called euthyroid sick syndrome or low T3 syndrome) is particularly common in hospitalized older adults and surgical patients. It produces low total T3 and sometimes low T4 with a paradoxically normal or low TSH, superficially resembling secondary or central hypothyroidism.

NTIS is generally an adaptive response (reduced metabolism during illness) rather than true thyroid insufficiency. Treating low T3 during critical illness with exogenous thyroid hormone has not been shown to improve outcomes and may worsen prognosis 9. Distinguishing NTIS from true structural thyroid disease (by testing TSH + free T4, not total T3, and repeating after recovery) is clinically important in elderly inpatients.

5. Thyroid autoimmunity and Hashimoto thyroiditis

The prevalence of thyroid autoantibodies — particularly anti-thyroid peroxidase (anti-TPO) antibodies — increases substantially with age and is higher in women throughout the lifespan. NHANES III data show anti-TPO positivity in approximately 11% of the total US population, rising with age, particularly in women past menopause 5.

Hashimoto-thyroiditis (chronic autoimmune thyroiditis) is the leading cause of hypothyroidism in iodine-sufficient regions. Lymphocytic infiltration of the thyroid, mediated by CD8+ cytotoxic T cells and Th1 CD4+ T cells targeting TPO, thyroglobulin, and TSH receptor, progressively destroys follicular architecture. The chronic-inflammation hallmark (SASP-like cytokine microenvironment in the thyroid) and disabled-adaptive-immunity hallmark (age-associated defects in immune self-tolerance) both contribute to the rising incidence with age.

Anti-TPO positivity without TSH elevation predicts future hypothyroidism: ~5%/year progression to overt hypothyroidism in antibody-positive individuals vs <1% in antibody-negative individuals 7. needs-replication — the exact progression rate in antibody-positive elderly subjects requires dedicated geriatric-cohort data.

6. Thyroid nodules and goiter

Thyroid nodules — focal lesions detectable by ultrasound — increase in prevalence with age and are extremely common in the elderly. Ultrasonographic studies in asymptomatic populations report prevalence of 40–60% in individuals over 60 years, compared with ~20% in younger adults 7. The vast majority are benign (colloid nodules, cysts, adenomas).

Thyroid cancer is found in approximately 23.6% of surgically resected nodules overall (858 of 3,629 resected cases in the Lin 2005 Taiwanese surgical series), rising to 37.2% in older patients (>65 years) 10. However, only 3.9% of all 21,748 evaluated subjects had histopathologically proven thyroid cancer — the higher per-resection rate reflects surgical selection bias (suspicious lesions are preferentially biopsied and resected), not population-level cancer risk. The approximately 4–5% figure sometimes cited in the general literature refers to unselected ultrasound-detected nodules across the population, which is a different denominator. unsourced — a primary epidemiological citation for the unselected-population malignancy rate is needed beyond this surgical series. Thyroid cancer incidence has risen globally in part due to incidental detection by imaging done for other indications — termed “incidentaloma effect.”

Goiter (diffuse or multinodular thyroid enlargement) prevalence also increases with age, particularly in areas with historically lower iodine intake. Multinodular goiter (MNG) can cause autonomous thyroid function — partial independence from TSH control — contributing to subclinical or overt hyperthyroidism in older adults (see § Hyperthyroidism below).

Clinical aging phenotypes

Hypothyroidism (overt)

Overt hypothyroidism (elevated TSH + low free T4) in older adults causes: bradycardia, cold intolerance, constipation, weight gain, hyponatremia, dyslipidemia (elevated LDL cholesterol), depression, cognitive slowing, myopathy, and, in severe cases, myxedema coma. Many of these features overlap with normal aging, making clinical diagnosis unreliable without biochemical testing in older patients 6.

Treatment with levothyroxine (synthetic T4) is unambiguous for overt hypothyroidism at any age. In older adults, starting doses should be low (12.5–25 µg/day) with gradual titration; excess levothyroxine in the elderly carries risks of atrial fibrillation, angina, and accelerated bone loss (see § Hyperthyroidism and bone below).

Subclinical hypothyroidism

Subclinical hypothyroidism (SCH) is defined biochemically as TSH elevated above the reference range with normal free T4 and T3. It is the most prevalent thyroid abnormality in older adults.

The treatment controversy — TRUST trial. Whether treating SCH improves outcomes in older adults was assessed by the double-blind randomized TRUST trial (n=737 adults ≥65 years with SCH; TSH inclusion range 4.60–19.99 mIU/L; mean TSH 6.40±2.01 mIU/L at baseline) 11. The trial randomized 369 to placebo and 368 to levothyroxine (starting dose 50 µg/day; 25 µg if weight <50 kg or known coronary heart disease), with dose adjustment targeting TSH 0.40–4.59 mIU/L. After one year, no significant differences were observed in either co-primary endpoint: the ThyPRO Hypothyroid Symptoms score (between-group difference 0.0; 95% CI −2.0 to 2.1; P=0.99) or the Tiredness score (between-group difference 0.4; 95% CI −2.1 to 2.9; P=0.77). Levothyroxine successfully normalized TSH (3.63±2.11 vs 5.48±2.48 mIU/L in placebo at 12 months; P<0.001) but this biochemical response did not translate into clinical benefit. Secondary outcomes (hand-grip strength, cognitive function by letter-digit coding test, blood pressure, weight, BMI) were also similar between groups. The minimum clinically important difference for each ThyPRO scale is 9 points; the 95% CI excluded a benefit greater than 2.1 points in either primary outcome. The TRUST trial is the highest-quality evidence available on this question and argues strongly against routine levothyroxine treatment for SCH in adults ≥65 years in the absence of symptom burden.

A subsequent meta-analysis (Moon 2018, 35 prospective cohort studies, n=555,530 participants) found that SCH was associated with modestly increased cardiovascular disease risk in the general population (relative risk 1.33) but no significant association with CVD or all-cause mortality in adults ≥65 years specifically 12. This age-specific null result parallels the TRUST clinical finding and is consistent with the TSH set-point hypothesis: mildly elevated TSH in the elderly may not represent the same degree of tissue hypothyroidism as in young adults.

Current guidance (post-TRUST): Most endocrine and geriatric societies now recommend against routine treatment of SCH in adults ≥65 years with TSH <10 mIU/L, unless there is symptom burden or rapid progression 4. Observation with repeat TSH testing is the default.

contradictory-evidence — Subgroup analyses from TRUST and observational data suggest possible benefit in the subset with TSH ≥7–8 mIU/L or with higher TPO antibody titers, but these were underpowered exploratory analyses; prospective trials needed.

Hyperthyroidism and bone loss

Hyperthyroidism — whether from Graves disease, toxic multinodular goiter (predominant in older adults), or exogenous levothyroxine overtreatment — accelerates bone remodeling disproportionately toward resorption, resulting in secondary osteoporosis 13. The mechanism involves: elevated T3 directly stimulating osteoclast differentiation via thyroid hormone receptors on osteoclast precursors; increased RANKL expression; and elevated bone alkaline phosphatase and collagen cross-link markers reflecting uncoupled high-turnover bone loss.

Fracture risk is elevated in untreated hyperthyroidism: data from cohort studies suggest up to 2-fold increased risk of hip and vertebral fractures, partially reversible with treatment 13. For older adults already at high fracture risk, even subclinical hyperthyroidism (low TSH, normal free T4/T3) warrants treatment consideration.

Graves disease typically presents in younger/middle-aged adults (female predominance, autoimmune; anti-TSH receptor antibodies). In contrast, toxic multinodular goiter and toxic adenoma — autonomous nodules that escape TSH feedback — are more common in older adults and often present as subclinical hyperthyroidism or atrial fibrillation in the absence of classic hyperthyroid symptoms (so-called “apathetic hyperthyroidism”).

Thyroid hormone, metabolism, and cognition

Thyroid hormones are essential regulators of basal metabolic rate, thermogenesis, and neurological function. Even mild hypothyroidism in older adults may contribute to cognitive slowing and depressive symptoms, though isolating this from normal aging is challenging given the symptomatic overlap. The TRUST trial found no cognitive benefit from levothyroxine at one year 11, but longer-term or higher-TSH-threshold studies have not been conducted.

Overt hypothyroidism is associated with reversible dementia-like symptoms (thyroid dementia), which respond to hormone replacement; distinguishing this from Alzheimer’s disease clinically requires TSH measurement. See alzheimers-disease for the differential diagnosis.

Hallmark connections

HallmarkThyroid mechanism
altered-intercellular-communicationThyroid hormones are systemic endocrine signals regulating metabolism, cardiac output, and bone turnover across all tissues; HPT axis dysregulation with age impairs this intercellular signaling layer
chronic-inflammationHashimoto thyroiditis: sustained lymphocytic thyroidal infiltration (Th1/cytotoxic CD8+ T cells, TPO-targeting antibodies) constitutes chronic organ-specific inflammation; thyroid SASP-like cytokines (IL-6, IL-1β, TNF-α) may amplify systemic inflammaging
disabled-adaptive-immunityAge-associated breakdown of immune self-tolerance permits expansion of autoreactive T and B cell clones targeting thyroid antigens (TPO, Tg, TSHR); the rising prevalence of anti-TPO antibodies with age directly reflects this hallmark

SENS frame: Thyroid hormone decline with aging is not directly in the SENS damage taxonomy (SENS focuses on intracellular and extracellular molecular damage); however, the autoimmune destruction of thyrocytes in Hashimoto thyroiditis could be framed as a maladaptive immune attack (analogous to ApoptoSENS failure modes).

Model organism note

Most thyroid biology is studied in mice (Mus musculus). Key caveats for human extrapolation:

DimensionStatus
HPT axis architecture conserved?Yes — TRH/TSH/T4/T3 feedback axis is highly conserved
Age-related TSH rise in mice?Partial — mice show some HPT axis changes with age but the magnitude and clinical significance differ; murine lifespan (~2–3 years) compresses the aging window
Autoimmune thyroiditis models?Yes — NOD.H-2h4 and other transgenic strains develop spontaneous autoimmune thyroiditis; mechanism is partially conserved but strain-specific
Clinical TSH reference range dataHuman-specific; not applicable to mouse

Extrapolate mouse thyroid signaling/mechanistic data with caution; human epidemiological and clinical trial data (NHANES III, TRUST) are the primary evidence base for clinical aging claims on this page.

Limitations and gaps

  • #gap/needs-replication — anti-TPO positivity to overt hypothyroidism progression rate in elderly subjects specifically; T3/T4 peripheral conversion decline and its clinical significance
  • #gap/contradictory-evidence — subclinical hypothyroidism treatment: TRUST trial shows null benefit in general ≥65 population; exploratory subgroups with TSH ≥7–8 mIU/L or high antibody titers may benefit — not tested in powered RCT
  • #gap/long-term-unknown — TRUST trial primary endpoint was at one year (median follow-up 17.3 months in placebo group; maximum 3 years); multi-year effects of untreated SCH on cognitive decline, bone loss, and cardiovascular events in the elderly are not settled
  • #gap/no-mechanism — why TSH set-point shifts upward with healthy aging (pituitary feedback vs gland reserve vs TSH isoform changes) is incompletely resolved
  • #gap/needs-human-replication — cellular senescence in thyroid follicular cells: whether thyrocytes accumulate p16^INK4a+^ senescent cells with age and whether SASP contributes to follicular dysfunction has not been characterized in human thyroid tissue
  • #gap/dose-response-unclear — optimal levothyroxine replacement dose target (TSH target range) in the elderly, particularly in the 65–80 vs >80 age bands, remains debated; most guidelines recommend TSH targets of 3–6 mIU/L in older adults rather than the young-adult 0.5–2.5 mIU/L range
  • #gap/unsourced — thyroid nodule ultrasonographic prevalence figures in adults >60 years (40–60% range; primary epidemiologic citation needed beyond 7 which is a review)

Cross-references

  • parathyroid — sibling gland; regulates calcium/PTH; shares anatomical neighborhood; functional interplay via calcium homeostasis (being seeded in parallel)
  • endocrine-system — parent system MOC (being seeded in parallel)
  • osteoporosis — phenotype downstream of hyperthyroidism-induced accelerated bone remodeling; see bone for mechanism
  • type-2-diabetes — metabolic comorbidity; insulin resistance and hypothyroidism co-occur and mutually worsen glycemic control
  • bone — thyroid hormone effects on bone remodeling; shared disease link via hyperthyroid osteoporosis
  • altered-intercellular-communication — hallmark MOC; thyroid as paradigm case of endocrine signal degradation with age
  • chronic-inflammation — hallmark MOC; Hashimoto thyroiditis as organ-specific inflammaging
  • disabled-adaptive-immunity — hallmark MOC; autoimmune thyroid disease as primary manifestation
  • alzheimers-disease — differential diagnosis for reversible “thyroid dementia” in hypothyroidism
  • frailty — hypothyroidism contributes to sarcopenia, fatigue, and frailty in older adults
  • cardiovascular-aging — thyroid-heart axis; hyperthyroidism as a driver of atrial fibrillation and bone loss; hypothyroidism as a driver of dyslipidemia

Footnotes

Footnotes

  1. doi:10.1007/BF03347076 · PMID 20834199 · Bonnema SJ, Fast S, Nielsen VE et al. · observational · n=170 patients with nodular goiter · J Endocrinol Invest 2011;34(7):e230–235 · Age correlated positively with thyroid volume (r=0.31, p<0.001); age and serum T4 (not volume or TSH) were primary determinants of radioiodine uptake; supports that thyroid volume increases modestly with age in nodular goiter ↩

  2. doi:10.1097/01.med.0000433055.99570.52 · PMID 23974775 · Tabatabaie V, Surks MI · review · Curr Opin Endocrinol Diabetes Obes 2013;20(5):420–424 · TSH increases with advancing age in both cross-sectional and longitudinal studies; definitive proof of harmful effects from SCH in elderly remains inconclusive; recommends caution in diagnosing thyroid disorders in geriatric populations ↩

  3. doi:10.1093/gerona/glw132 · PMID 27440910 · Yeap BB, Manning L, Chubb SAP et al. · observational · n=3,885 community-dwelling men aged 70–89 · J Gerontol A Biol Sci Med Sci 2017;72(3):444 (published online 2016) · TSH 2.5th–97.5th centile in older men = 0.64–5.9 mIU/L vs conventional adult 0.4–4.0 mIU/L; applying age-specific range reclassified ~8% of men; higher free T4 (not TSH elevation) associated with increased mortality in this cohort ↩

  4. doi:10.1016/bs.vh.2020.12.001 · Duntas LH · book chapter · Vitamins and Hormones 115:1–14 · 2021 · Review of HPT axis aging; morphological and functional changes are a natural adaptation to aging; advocates geroscience framework for thyroid management; emphasizes personalized TSH targets in elderly ↩ ↩2

  5. doi:10.1210/jcem.87.2.8182 · PMID 11836274 · Hollowell JG, Staehling NW, Flanders WD et al. · observational · n=17,353 · model: US general population (NHANES III, 1988–1994) · J Clin Endocrinol Metab 2002;87(2):489–499 · Prevalence: subclinical hypothyroidism 4.3%, overt hypothyroidism 0.3%, subclinical hyperthyroidism 0.7%, overt hyperthyroidism 0.5%; anti-TPO positive in 11.3% of participants; prevalence of antibodies and hypothyroidism higher in women and increasing with age ↩ ↩2

  6. doi:10.2174/1871530323666230828110153 · PMID 37641994 · Fiore V, Barucca A, Barraco S et al. · review · Endocr Metab Immune Disord Drug Targets 2024;24(8):879–884 · Narrative review of hypothyroidism in older adults; prevalence is “one of the most common comorbidities among patients over 75”; recommends TSH targets typically maintained above 3 mIU/L in elderly; discusses personalized levothyroxine dosing ↩ ↩2

  7. doi:10.1210/er.2006-0043 · PMID 17991805 · Biondi B, Cooper DS · review (527 references) · Endocr Rev 2008;29(1):76–131 · Comprehensive review of subclinical thyroid dysfunction; summarizes prevalence, natural history (anti-TPO+ individuals progress to overt hypothyroidism at ~5%/yr), cardiovascular and bone effects, and treatment controversies; covers both subclinical hypo- and hyperthyroidism across age groups ↩ ↩2 ↩3 ↩4

  8. doi:10.1007/BF02790145 · PMID 8834378 · Olivieri O, Girelli D, Stanzial AM et al. · observational · n=elderly vs young adults · model: community-dwelling humans · Biol Trace Elem Res 1996;51(1):31–41 · Low T3/T4 ratio in elderly correlated with reduced selenium and RBC glutathione peroxidase activity; 5’-deiodinase (selenium-dependent) activity declines with age; impaired selenium status partially explains reduced T4→T3 peripheral conversion in older adults ↩ ↩2

  9. doi:10.3389/fendo.2019.00258 · PMID 31068905 · Vacante M, Biondi A, Basile F et al. · review · Front Endocrinol 2019;10:258 · Non-thyroidal illness (low T3 syndrome) common in hospitalized older adults; low T3 is a predictor of low cardiac output and mortality; treating NTIS with exogenous thyroid hormone does not improve outcomes; diagnosis requires free T4 + TSH (not total T3), repeated after recovery ↩ ↩2

  10. doi:10.1089/thy.2005.15.708 · PMID 16053388 · Lin JD, Chao TC, Huang BY et al. · observational · n=21,748 subjects evaluated (3,629 surgically resected; 1986–1999) · model: Taiwanese surgical patients with thyroid nodules · Thyroid 2005;15(7):708–717 · 16.7% of evaluated subjects underwent surgical resection; malignancy in 23.6% of resected nodules overall (858/3,629); malignancy rate in elderly (>65 years: 37.2% of resected nodules) — highest of all age groups, reflecting surgical selection bias (suspicious lesions preferentially resected), not population cancer prevalence; 3.9% of all 21,748 evaluated subjects had histopathologically proven thyroid cancer ↩

  11. doi:10.1056/NEJMoa1603825 · PMID 28402245 · Stott DJ, Rodondi N, Kearney PM et al. · randomized · n=737 (369 placebo / 368 levothyroxine; ≥65 years; 53.7% women; mean age 74.4 years; mean baseline TSH 6.40±2.01 mIU/L; inclusion TSH 4.60–19.99 mIU/L) · p=0.99 (Hypothyroid Symptoms) and p=0.77 (Tiredness) for co-primary endpoints · N Engl J Med 2017;376(26):2534–2544 (TRUST trial) · Double-blind parallel-group RCT; levothyroxine (starting dose 50 µg; 25 µg if <50 kg or known CHD) vs placebo for minimum 1 year (maximum 3 years; median follow-up 17.3 months in placebo group); primary endpoints (ThyPRO Hypothyroid Symptoms score and Tiredness score, each 0–100; MCID=9 points): between-group difference 0.0 (95% CI −2.0 to 2.1) and 0.4 (95% CI −2.1 to 2.9), respectively — no significant improvement in levothyroxine arm; TSH normalized (3.63±2.11 vs 5.48±2.48 mIU/L at 12 months; P<0.001) without clinical benefit; secondary outcomes (grip strength, letter-digit coding, blood pressure, BMI) also null; no significant excess of serious adverse events of special interest (AF, heart failure, fracture, new osteoporosis); key evidence against routine treatment of SCH in older adults ↩ ↩2

  12. doi:10.1089/thy.2017.0414 · PMID 29978767 · Moon S, Kim MJ, Yu JM et al. · meta-analysis · n=555,530 (35 prospective cohort studies) · Thyroid 2018;28(9):1101–1110 · Subclinical hypothyroidism associated with modest CVD risk increase in general population (RR 1.33) and all-cause mortality (RR 1.20); no significant association in adults ≥65 years specifically; elevated risks in high-CVD-risk patients ↩

  13. doi:10.1055/a-1088-1215 · PMID 31958849 · Lademann F, Tsourdi E, Hofbauer LC, Rauner M · review · Exp Clin Endocrinol Diabetes 2020;128(6-07):450–454 · Thyroid hormones are essential for bone mass maintenance; hyperthyroidism causes secondary osteoporosis via enhanced osteoclast activity, RANKL upregulation, and uncoupled high-turnover bone loss; Wnt pathway implicated as therapeutic target; bone effects partially reversible with treatment ↩ ↩2

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