Each May 25, World Thyroid Day raises awareness about the small neck gland that controls growth, metabolism and brain development. The 2026 theme stresses early detection and fair access to thyroid care, yet a deeper history deserves attention. It involves iodine, a trace heavy element essential for body function. Its discovery and use in public health raised humanity’s average intelligence during the past century.
The account starts amid conflict. During the Napoleonic Wars, Britain blockaded France from 1806 to 1814, creating shortages of potassium nitrate for gunpowder. Bernard Courtois processed seaweed ash for alkali and noticed violet vapors in 1811. These proved to be iodine. Joseph Louis Gay-Lussac later named it after the Greek word for violet-colored. Humphry Davy verified it as a new element in 1813.
Early uses mixed wound tinctures with fears of toxicity. In 1820 Geneva, Jean-François Coindet linked seaweed remedies to reduced neck swelling and tried iodine solutions for goitres, though wrong doses caused setbacks. In 1914 Heinrich Hunziker correctly established iodine as a dietary micronutrient needed in small amounts, clarifying its role against goitre.
Iodine distribution is uneven. Abundant in oceans, it is scarce in inland and mountainous soils washed by glaciers or floods. Crops there lack the element, so distant populations suffer chronic shortage. Areas such as the Himalayas from Kashmir to Arunachal Pradesh historically showed high goitre and developmental delay rates.
Understanding of the thyroid advanced through observations. Thomas Wharton described the gland in 1656. Theodor Kocher noted that total removal caused physical and mental slowing, later called myxoedema, earning a 1909 Nobel. George R. Murray used thyroid extract in 1891. Eugen Baumann found iodine concentrated in the gland around 1895. Edward Calvin Kendall isolated thyroxine in 1914, identifying T3 and T4.
These hormones require iodine. The pituitary releases TSH to stimulate production; sufficient levels trigger feedback suppression. Deficiency enlarges the gland yet fails to produce enough hormone. In pregnancy the foetus relies on maternal supply for the first six months, so lack impairs brain growth and yields lower intelligence. Iodine deficiency ranks as a preventable cause of intellectual disability, though excess can trigger hyperthyroidism. Benefits occur only when correcting shortage.
David Marine promoted salt as the delivery vehicle in the United States in 1917. Salt reaches nearly everyone daily in steady amounts. Added iodine, usually as potassium iodate, leaves taste, colour and cooking unchanged. It is also cheap, making it suitable for mass use.
