Iodide as an antioxidant

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Iodide can function as an antioxidant as it is a reducing species that can detoxify reactive oxygen species such as hydrogen peroxide.

Over three billion years ago, blue-green algae were the most primitive oxygenic photosynthetic organisms and are the ancestors of multicellular eukaryotic algae (1). Algae that contain the highest amount of iodine (1-3 % of dry weight) and peroxidase enzymes, were the first living cells to produce poisonous oxygen in the atmosphere (2, 3). Therefore algal cells required a protective antioxidant action of their molecular components, in which iodides, through peroxidase enzymes, seem to have had this specific role (4, 5). In fact, iodides are greatly present and available in the sea, where algal phytoplankton, the basis of marine food-chain, acts as a biological accumulator of iodides, selenium, (and n-3 fatty acids) (6, 7, 8):

Antioxidant biochemical mechanism of iodides (1, 5)

2 I- -> I2 + 2 e- (electrons) = - 0.54 Volt ;

2 I- + Peroxidase + H2O2 + 2 Tyrosine -> 2 Iodo-Tyrosine + H2O + 2 e- (antioxidants);

2 e- + H2O2 + 2 H+ (of intracellular water-solution) -> 2 H2O

Antioxidant biochemical mechanism of iodides, probably one of the most ancient mechanisms of defense from poisonous reactive oxygen species (6, 7)

2 I- + Peroxidase + H2O2 + Tyrosine, Histidine, Lipids, Carbons -> Iodo-Compounds + H2O + 2 e- (antioxidants)

Iodo-Compounds: Iodo-Tyrosine, Iodo-Histidine, Iodo-Lipids, Iodo-Carbons


1. Venturi S, Venturi M. Iodide, thyroid and stomach carcinogenesis: evolutionary story of a primitive antioxidant? Eur J Endocrinol. 1999 Apr;140(4):371-2. N PMID: 10097259

2. Küpper FC, Feiters MC, Meyer-Klaucke W, Kroneck PMH, Butler A (2002) Iodine Accumulation in Laminaria (Phaeophyceae): an Inorganic Antioxidant in a Living System? Proceedings of the 13th Congress of the Federation of European Societies of Plant Physiology, Heraklion, Greece, September 2-6, p. 571

3. Küpper FC, Schweigert N, Ar Gall E, Legendre J-M, Vilter H, Kloareg B (1998) Iodine uptake in Laminariales involves extracellular, haloperoxidase-mediated oxidation of iodide. Planta 207:163-171

4. Ar Gall, E., Küpper, F.C. & Kloareg, B. (2004). A survey of iodine content in Laminaria digitata. Botanica Marina 47: 30-37.

5. Venturi S, Donati FM, Venturi A, Venturi M. Environmental iodine deficiency: A challenge to the evolution of terrestrial life? Thyroid. 2000 Aug;10(8):727-9. PMID: 11014322

6. Venturi S. and Venturi M. “Iodine and Evolution”. DIMI-MARCHE NEWS, Dipartimento Interaziendale di Medicina Interna della Regione Marche (Italy), published on-line, Feb. 8, 2004:

7. Venturi S, Donati FM, Venturi A, Venturi M, Grossi L, Guidi A. Role of iodine in evolution and carcinogenesis of thyroid, breast and stomach. Adv Clin Path. 2000 Jan;4(1):11-7. PMID: 10936894

8. Venturi S, Venturi M. Evolution of Dietary Antioxidant Defences. European EPI-Marker. 2007, 11, 3 :1-12