Does iodine gas released from seaweed contribute to dietary iodine intake?
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Thyroid hormone levels sufficient for brain development and normal metabolism require a minimal supply of iodine, mainly dietary. Living near the sea may confer advantages for iodine intake. Iodine (I2) gas released from seaweeds may, through respiration, supply a significant fraction of daily iodine requirements. Gaseous iodine released over seaweed beds was measured by a new gas chromatography–mass spectrometry (GC–MS)-based method and iodine intake assessed by measuring urinary iodine (UI) excretion. Urine samples were obtained from female schoolchildren living in coastal seaweed rich and low seaweed abundance and inland areas of Ireland. Median I2 ranged 154–905 pg/L (daytime downwind), with higher values (~1,287 pg/L) on still nights, 1,145–3,132 pg/L (over seaweed). A rough estimate of daily gaseous iodine intake in coastal areas, based upon an arbitrary respiration of 10,000L, ranged from 1 to 20 μg/day. Despite this relatively low potential I2 intake, UI in populations living near a seaweed hotspot were much higher than in lower abundance seaweed coastal or inland areas (158, 71 and 58 μg/L, respectively). Higher values >150 μg/L were observed in 45.6% of (seaweed rich), 3.6% (lower seaweed), 2.3% (inland)) supporting the hypothesis that iodine intake in coastal regions may be dependent on seaweed abundance rather than proximity to the sea. The findings do not exclude the possibility of a significant role for iodine inhalation in influencing iodine status. Despite lacking iodized salt, coastal communities in seaweed-rich areas can maintain an adequate iodine supply. This observation brings new meaning to the expression “Sea air is good for you!”
KeywordsAtmospheric gaseous iodine Thyroid Urinary iodine Seaweed Iodine
The authors gratefully acknowledge the cooperation of the parents and schoolchildren of participating schools in both the Republic of Ireland and Northern Ireland. We greatly appreciate the assistance of the HSE, West, Dr Karla Kyne, Area Community Medical Officer for the Carna Area, Dr Mary FitzGerald, Senior Medical Officer Primary, Community & Continuing Care. Dr John O’Donnell of Galway and Richard Fitzgerald of the Martin Ryan Institute, NUI, Galway. Thanks to Professor Edward Limbert for helpful discussion re Portuguese data. Financial assistance was provided by the Health Research Board, Ireland and the Clinical Endocrinology Trust.
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