What Is Hypothyroidism?
Hypothyroidism is a clinical condition resulting from insufficient production of thyroid hormones (T4 — thyroxine and T3 — triiodothyronine) by the thyroid gland. These hormones regulate the basal metabolism of virtually all cells in the body, and their deficiency causes generalized slowing of bodily functions.
It is the most common endocrine disorder, affecting 5-10% of the adult population, with a 5-8:1 female predominance. Prevalence increases with age, reaching 10-15% in women over age 60. The most frequent cause worldwide is Hashimoto thyroiditis — an autoimmune disease that progressively destroys thyroid tissue.
Hypothyroidism may be primary (failure of the thyroid itself — 95% of cases), secondary (TSH deficiency from pituitary disease), or tertiary (TRH deficiency from hypothalamic disease). Subclinical hypothyroidism — elevated TSH with normal free T4 — affects up to 10% of women and represents an early stage of the disease.
Global Metabolism
Thyroid hormones regulate the metabolism of all tissues: basal metabolic rate, thermogenesis, heart rate, intestinal motility, cognitive function, and mood.
Autoimmunity as Cause
Hashimoto thyroiditis is the most common cause. Anti-TPO and anti-thyroglobulin antibodies progressively attack the thyroid, leading to glandular destruction and hypofunction.
Simple and Effective Treatment
Levothyroxine replacement completely normalizes thyroid function in the vast majority of patients. It is one of the most cost-effective treatments in medicine.
Pathophysiology
The thyroid mainly produces T4 (thyroxine), a long-half-life pro-hormone (7 days) that is peripherally converted to T3 (triiodothyronine), the biologically active form. T3 binds to nuclear receptors in virtually all cells, regulating the expression of hundreds of genes involved in energy metabolism.
The hypothalamic-pituitary-thyroid axis regulates hormone production: the hypothalamus secretes TRH, which stimulates the pituitary to produce TSH, which stimulates the thyroid to produce T4/T3. When T4/T3 fall, TSH rises through negative feedback — that is why elevated TSH is the most sensitive marker of primary hypothyroidism.
Hashimoto Thyroiditis
In Hashimoto thyroiditis, autoreactive T lymphocytes infiltrate the thyroid gland and, together with anti-TPO and anti-thyroglobulin antibodies, destroy thyrocytes (the hormone-producing cells). Destruction is gradual — it takes years until functional reserve is insufficient to maintain normal hormone levels.
The typical progression is: euthyroid phase with positive antibodies (years), subclinical hypothyroidism (elevated TSH, normal free T4), and finally overt hypothyroidism (elevated TSH, low free T4). Not all patients with Hashimoto progress to overt hypothyroidism — some remain subclinical indefinitely.
Symptoms
The symptoms of hypothyroidism reflect a global reduction in metabolism: everything slows down — the heart, the gut, thinking, reflexes. Symptoms are frequently attributed to aging, depression, or stress, delaying diagnosis.
Symptoms of Hypothyroidism
- 01
Persistent fatigue and tiredness
Tiredness that does not improve with rest, sensation of lacking energy for usual activities. It is the most common symptom and frequently the first to appear.
- 02
Cold intolerance
Excessive sensitivity to cold, need for warm clothing when others are comfortable. Results from reduced thermogenesis due to hormonal deficit.
- 03
Weight gain
Modest weight gain (3-5 kg) due to reduced basal metabolism and water retention (myxedema). Hypothyroidism does not cause obesity — larger gains require additional investigation.
- 04
Constipation
Slowing of intestinal motility (peristalsis). Frequently one of the most uncomfortable complaints and one of the first to improve with treatment.
- 05
Dry skin and brittle hair
Dry, rough, and flaky skin. Thin, brittle hair with increased shedding. Fragile, ridged nails. Result from reduced cell turnover.
- 06
Bradycardia and cognitive changes
Low heart rate (below 60 bpm), slowed thinking, difficulty concentrating, and memory lapses. In severe cases, lethargy and myxedema coma.
Diagnosis
Diagnosis is laboratory-based: TSH is the most sensitive test and should be the first ordered. An elevated TSH with low free T4 confirms primary hypothyroidism. Anti-TPO antibodies identify the autoimmune etiology (Hashimoto).
Thyroid ultrasound may show reduced volume and heterogeneous echogenicity in Hashimoto thyroiditis, but it is not necessary for diagnosis in most cases. It is indicated when there are palpable nodules or a goiter. The lipid panel is important — hypercholesterolemia is a frequent metabolic consequence of hypothyroidism.
🏥Laboratory Classification of Hypothyroidism
- 1.Overt hypothyroidism: elevated TSH (> 10 mIU/L) + low free T4
- 2.Subclinical hypothyroidism: elevated TSH (4.5-10 mIU/L) + normal free T4
- 3.Positive anti-TPO: confirms autoimmune etiology (Hashimoto) in 90%+ of cases
- 4.Central hypothyroidism (secondary/tertiary): low free T4 with low or inappropriately normal TSH
- 5.Lipid panel: frequent hypercholesterolemia — should be monitored and reassessed after treatment
DIAGNÓSTICO DIFERENCIAL
Diagnóstico Diferencial
Subclinical Hypothyroidism
- Elevated TSH (4-10 mIU/L)
- Normal free T4
- Symptoms absent or minimal
- High prevalence in older adults
Testes Diagnósticos
- TSH, free T4
- Anti-TPO (predicts progression)
- Reassessment in 3-6 months
Acupuncture may be useful in symptomatic subclinical hypothyroidism while a decision is being made about hormone replacement.
Hashimoto Thyroiditis
- Most common cause of hypothyroidism
- Firm, painless goiter
- Strongly positive anti-TPO
- Fluctuating course
Testes Diagnósticos
- Anti-TPO and anti-Tg
- Thyroid US (heterogeneous pattern)
- TSH and free T4
Preliminary studies suggest a possible immunomodulatory effect of acupuncture in Hashimoto, with reports of antibody reduction in some trials — evidence still limited; does not replace hormone replacement.
Sick Euthyroid Syndrome
- Low T3 in severe systemic illness
- Normal or low TSH
- ICU, sepsis, surgery setting
- No thyroid disease
Testes Diagnósticos
- Free T3, TSH, free T4
- Reassessment after recovery from acute illness
Depression (Overlapping Symptoms)
- Fatigue
- Depressed mood
- Weight gain
- Anhedonia
- Normal TSH
Testes Diagnósticos
- TSH, free T4 (rule-out)
- Depression scales (PHQ-9)
- Psychiatric evaluation
Acupuncture is effective for both depression and fatigue — may benefit even when TSH is normal.
Metabolic Syndrome
- Abdominal obesity
- Hypertriglyceridemia
- Low HDL
- Hypertension
- Altered glycemia
Testes Diagnósticos
- TSH (rule-out hypothyroidism)
- Lipid panel
- Fasting glycemia
- Abdominal circumference
Hashimoto vs. Other Causes of Hypothyroidism
Hashimoto thyroiditis is the most common cause of hypothyroidism in the developed world, accounting for 80-90% of cases. Diagnosis is confirmed by the combination of elevated TSH + low free T4 + positive anti-TPO. The heterogeneous echographic pattern with diffuse hypoechogenicity is characteristic. Levothyroxine replacement is the standard treatment — there is no established specific treatment for the autoimmunity. Some preliminary studies report a possible immunomodulatory effect of acupuncture, with reductions in anti-TPO antibodies in small samples — results not yet confirmed by robust systematic reviews.
Subclinical hypothyroidism (TSH between 4-10 mIU/L with normal free T4) is a clinical dilemma. The decision to treat depends on context: symptomatic patients, pregnancy, positive anti-TPO (high risk of progression), and TSH > 10 are consensus indications. In asymptomatic patients with TSH 4-10, watchful waiting with reassessment in 6-12 months is a reasonable option.
Depression and Hypothyroidism: A Common Differential
Symptomatic overlap between depression and hypothyroidism is significant — fatigue, weight gain, cognitive slowing, and depressed mood are present in both. TSH is the mandatory screening test before starting antidepressants. Important: some patients with Hashimoto and normal TSH still have hypothyroid symptoms (symptomatic hypothyroidism with normal TSH), likely from impaired T4-to-T3 conversion.
Sick euthyroid syndrome occurs in severe systemic illnesses and can mimic hypothyroidism on laboratory tests. Treatment with levothyroxine in this context is controversial and generally not recommended — the pattern resolves with recovery from the underlying illness.
Sick Euthyroid Syndrome
Sick euthyroid syndrome (also called non-thyroidal illness syndrome — NTIS) is a laboratory pattern frequently encountered in patients hospitalized in critical condition — sepsis, decompensated heart failure, major surgery, or extensive trauma. The central mechanism is inhibition of type 1 deiodinase by systemic stress, reducing peripheral conversion of T4 to active T3 and increasing reverse T3 (biologically inactive). The result is low total T3 with normal or mildly altered T4 and TSH — a pattern that can be erroneously interpreted as central hypothyroidism if the clinical context is not considered.
Distinction from true hypothyroidism is critical: in NTIS, the laboratory pattern normalizes spontaneously with recovery from the underlying illness, without need for hormone replacement. Randomized studies have shown no benefit — and suggest potential harm — with levothyroxine in NTIS. The acupuncture physician should not initiate or maintain thyroid hormone replacement based on an altered thyroid panel from a critically ill patient, and should request reassessment after clinical recovery.
Treatment
The standard treatment is replacement with levothyroxine (synthetic T4) in a single daily dose, on an empty stomach, 30-60 minutes before breakfast. The dose is adjusted by TSH, with the goal of keeping it within the normal range (0.4-4.0 mIU/L in most patients).
Treatment Initiation
Levothyroxine 1.6 mcg/kg/day as a full replacement dose in healthy young adults. In older adults and those with cardiac disease, start with 25-50 mcg/day and increase gradually every 4-6 weeks. Take on an empty stomach with water.
Dose Adjustment
TSH should be measured 6 weeks after initiation or dose adjustment. The dose is titrated until TSH reaches the target range. After stabilization, annual TSH. Factors that change requirements: pregnancy (30-50% increase), aging, concomitant medications.
Special Situations
Pregnancy: TSH target < 2.5 mIU/L in the 1st trimester. Older adults: avoid TSH suppression (risk of atrial fibrillation and osteoporosis). Central hypothyroidism: monitor by free T4, not by TSH.
Complementary Approaches
Acupuncture as adjunct for residual symptoms (fatigue, mood changes), selenium supplementation (200 mcg/day may reduce anti-TPO in Hashimoto), vitamin D (deficiency is associated with thyroid autoimmunity), regular physical exercise.
Acupuncture as Treatment
Acupuncture in hypothyroidism has been investigated as adjunctive therapy, with potential focus on improvement of residual symptoms that persist despite normalized TSH (fatigue, mood, cognition). Possible effects on immunologic activity remain under investigation.
Some experimental studies suggest that acupuncture may influence regulatory T-cell activity and cytokine production — preliminary data not yet sufficiently validated. Preliminary clinical studies in Hashimoto show heterogeneous findings, and evidence is limited.
Acupuncture does not replace levothyroxine — hormone replacement is indispensable. It may be considered as a complement for patients who, despite normalized TSH, continue to have symptoms such as chronic fatigue, mood changes, or difficulty concentrating. These residual symptoms affect up to 10-15% of treated patients.
Prognosis
The prognosis of treated hypothyroidism is excellent. Levothyroxine replacement completely normalizes metabolism, and life expectancy is identical to that of the general population. Most patients return to full well-being within weeks to months of starting treatment.
Treatment is, in most cases, permanent — the Hashimoto-destroyed thyroid does not regenerate. However, in subclinical hypothyroidism with negative anti-TPO, there is the possibility of spontaneous TSH normalization in up to 30% of cases, justifying periodic reassessment.
Chronically untreated hypothyroidism can lead to dyslipidemia with accelerated atherosclerosis, myxedematous cardiomyopathy, peripheral neuropathy and, in extreme cases, myxedema coma (an endocrine emergency with 20-40% mortality). Early diagnosis and treatment prevent all these complications.
Myths and Facts
Myth vs. Fact
Hypothyroidism is the main cause of obesity
Hypothyroidism causes modest weight gain (3-5 kg), mainly from water retention. Significant obesity requires additional investigation and should not be attributed exclusively to the thyroid.
Anyone on thyroid medication can never stop
In most cases (Hashimoto), treatment is in fact permanent. However, in subclinical hypothyroidism without autoimmunity or transient hypothyroidism (post-thyroiditis), spontaneous normalization may occur.
Levothyroxine causes weight gain or weight loss
Levothyroxine normalizes metabolism. Hypothyroid patients may lose the 3-5 kg gained from the disease, but they do not lose more than that. Levothyroxine is not a weight-loss medication, and its use without indication is dangerous.
Foods like soy and kale harm the thyroid
Dietary goitrogens (soy, cruciferous vegetables) in normal dietary amounts do not cause hypothyroidism in people with adequate iodine intake. They are only relevant with extreme consumption or iodine deficiency.
Subclinical hypothyroidism always needs treatment
Not always. The decision is individualized. For TSH between 4.5 and 10 without symptoms and without anti-TPO, observation with regular monitoring is a valid and safe option.
When to Seek Help
Untreated hypothyroidism can cause serious complications, and myxedema coma is a medical emergency.
Frequently Asked Questions about Hypothyroidism
In most cases of permanent hypothyroidism (Hashimoto, post-thyroidectomy, post-radioiodine), yes. Mild subclinical hypothyroidism may not require permanent treatment and should be reassessed periodically. The decision belongs to the endocrinologist, based on TSH, symptoms, and the cause of hypothyroidism.
Levothyroxine is absorbed in the jejunum and duodenum on an empty stomach. Food (especially calcium, iron, and fiber), coffee, and several medications significantly reduce absorption. It should be taken 30-60 minutes before breakfast, with water. Lack of fasting adherence is the most common cause of persistently elevated TSH in patients on treatment.
Preliminary studies suggest a possible immunomodulatory effect of acupuncture in Hashimoto thyroiditis, with reports of reduced anti-TPO antibodies in some trials — but evidence is still limited and heterogeneous, and does not constitute established treatment. Acupuncture may be evaluated as adjunctive for residual symptoms (fatigue, mood) that persist despite normalized TSH. It never replaces levothyroxine — hormone replacement is indispensable. The acupuncture physician evaluates the indication on an individualized basis.
There is an association between celiac disease and Hashimoto thyroiditis (greater frequency of positive anti-TPO in celiac patients). In celiac patients with Hashimoto, a gluten-free diet may reduce antibody titers. However, for people without celiac disease or proven gluten sensitivity, there is no evidence that gluten causes or worsens hypothyroidism.
Yes, but generally modestly (2-4 kg). Weight gain in hypothyroidism is mainly from water retention and myxedema, not fat accumulation. Most patients do not lose substantial weight from hormone replacement alone — additional lifestyle interventions are needed.
Yes. Uncontrolled hypothyroidism increases the risk of anovulatory cycles, infertility, miscarriage, and obstetric complications. The TSH target during pregnancy is stricter (< 2.5 mIU/L in the 1st trimester). Women planning pregnancy should have hypothyroidism optimized before conception.
It depends on the context. Consensus indications for treatment: TSH > 10 mIU/L, symptoms, pregnancy or pregnancy planning, positive anti-TPO (greater risk of progression), and presence of cardiovascular comorbidities. For asymptomatic TSH 4-10, management is individualized by the physician.
Raw cruciferous vegetables in large quantities (kale, broccoli, cabbage) contain goitrogens that may interfere with hormone synthesis — cooking neutralizes them. Excess soy may reduce levothyroxine absorption. Calcium and iron should be taken away from levothyroxine (a 2-4 hour interval). There is no mandatory restrictive diet — adequate hormonal control is what matters most.
Yes. A subgroup of patients with Hashimoto remains symptomatic even with TSH within the normal range — possibly from impaired T4-to-T3 conversion (cellular hypothyroidism). In these cases, the physician may consider adding liothyronine (T3) to levothyroxine or using desiccated thyroid extracts. Acupuncture may help with residual symptoms.
In Hashimoto thyroiditis, there is a progressive decline in thyroid function over the years, requiring gradual adjustment of levothyroxine doses. Annual TSH screening is recommended in patients with Hashimoto. Older adults often need lower doses of levothyroxine due to reduced metabolic clearance.
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