Iodine

Iodine is an essential trace element required for the synthesis of thyroid hormones (thyroxine [T₄] and triiodothyronine [T₃]), which regulate basal metabolism, growth, and neurodevelopment. In humans, it is primarily obtained from the diet and, when deficient, can impair thyroid function and downstream physiological processes.

• Elemental Iodine: Iodine (elemental) is a diatomic halogen with the molecular formula I₂; the IUPAC name is simply iodine.
• Supplement Form: In supplements, the biologically active form is the iodide ion (I⁻), often supplied as potassium iodide (KI) or sodium iodide (NaI).
• Properties: The atomic weight of iodine is 126.90 g/mol, and it has a melting point of 113.7 °C and a boiling point of 184.3 °C. Iodine is a non‑metal with a violet‑brown color in solid form and sublimates readily.
• Ion Characteristics: The ion has a monovalent negative charge, a relatively large ionic radius (2.06 Å), and high polarizability, which underlies its strong affinity for the NIS transporter.
• Redox Properties: In aqueous solution, iodide can be oxidized to iodine, which can then be reduced back, making it a useful redox couple in biological systems.

• Extraction: Commercial iodine is primarily extracted from iodine‑rich brine deposits (e.g., Chilean and Japanese salt lakes) where it is recovered by oxidation of iodide with chlorine, followed by purification and crystallization.
• Natural Sources: Marine algae (kelp, seaweed) provide natural organic forms of iodine (as iodophenols and iodinated lipids) and are used in “kelp extract” supplements; these require careful processing to remove heavy metals and ensure consistent iodine content.
• Synthetic Production: Synthetic production of KI and NaI is achieved via the reaction of elemental iodine with potassium or sodium hydroxide, yielding high‑purity salts suitable for pharmaceutical use.
• Quality Control: Quality control focuses on pharmacopoeial specifications (e.g., USP <467>), ensuring ≤ 10 ppm heavy metal content, accurate labeling of iodine content (± 5 %), and the absence of contaminants such as bromide or arsenic.