The thyroid gland — a butterfly-shaped structure at the base of the neck — produces thyroid hormones (T3 and T4) that regulate metabolism, heart rate, temperature, mood, and the function of virtually every organ system. When thyroid hormone production is inadequate (hypothyroidism) or excessive (hyperthyroidism), the physiological consequences ripple broadly through the body. Thyroid disorders affect an estimated 200 million people globally, with women being five to eight times more frequently affected than men.
Hypothyroidism
Hypothyroidism — inadequate thyroid hormone — most commonly results from Hashimoto's thyroiditis (autoimmune destruction of the gland) or treatment of hyperthyroidism. Symptoms develop gradually and are often attributed to other causes: unexplained fatigue and sluggishness; weight gain despite no change in diet; sensitivity to cold; constipation; dry skin and brittle hair; depression and cognitive slowing ("brain fog"); slowed heart rate; elevated cholesterol; and in women, menstrual irregularities. Diagnosis is straightforward: an elevated TSH (thyroid-stimulating hormone) with low free T4 confirms primary hypothyroidism. Treatment with levothyroxine — synthetic T4 — is highly effective, usually lifelong, and restores normal thyroid hormone levels with minimal side effects when properly dosed.
Hyperthyroidism
Hyperthyroidism — excess thyroid hormone — most commonly results from Graves' disease (autoimmune stimulation of the thyroid), toxic multinodular goitre, or a single autonomous "hot" nodule. Symptoms reflect accelerated metabolism: unintentional weight loss despite increased appetite; heat intolerance and excessive sweating; palpitations, rapid heart rate (sometimes atrial fibrillation); tremor; anxiety and irritability; frequent bowel movements; and exophthalmos (eye protrusion) in Graves' disease. Treatment options include antithyroid medications (methimazole, propylthiouracil), radioactive iodine ablation, or surgical thyroidectomy — choice depends on aetiology, severity, patient age, and preferences.
Thyroid Nodules and Cancer
Thyroid nodules are extremely common — detectable by ultrasound in up to 68% of adults — but the vast majority are benign. Cancer is found in approximately 7–15% of biopsied nodules. Papillary thyroid carcinoma accounts for approximately 80% of thyroid cancers and has an excellent prognosis (10-year survival >95%) because it typically grows slowly and responds well to surgery and radioactive iodine. Ultrasound characterisation and fine-needle aspiration biopsy guide the decision to monitor versus remove suspicious nodules.
Frequently Asked Questions
Can diet affect thyroid function?
Yes, in specific ways. Iodine deficiency — the world's leading preventable cause of hypothyroidism — is rare in developed countries due to iodised salt, but remains a global issue. Excessive iodine intake can paradoxically impair thyroid function. Cruciferous vegetables contain goitrogens that theoretically inhibit thyroid hormone synthesis, but only in very large quantities — routine consumption poses no significant risk to individuals with adequate iodine status.
Should all thyroid nodules be biopsied?
No. Decision to biopsy is guided by nodule size, ultrasound characteristics (composition, echogenicity, margins, calcifications, vascularity), and clinical context using standardised reporting systems (TIRADS, ACR TIRADS, ATA guidelines). Many small nodules with benign characteristics can be monitored with serial ultrasound without biopsy.
Sources
- American Thyroid Association. Hypothyroidism Booklet. 2022.
- Biondi B, et al. Subclinical Hypothyroidism — A Mild Form of Thyroid Failure. Lancet. 2022.
- Mayo Clinic. Thyroid disease. 2023.