Bioavailability of seaweed iodine in human beings

The major procedure used to correct iodine deficiency is the universal salt iodization by addition of iodide or iodate to salt with an iodine content varying from 7 to 100 mg/kg of salt depending on the country legislation. As an important fraction of consumers in the world prefers natural products over artificial ones, we investigated the industrial feasibility of naturally iodized salt using seaweed as source of iodine. We report the results of the iodine bioavailability in healthy subjects from two seaweeds: Laminaria hyperborea and Gracilaria verrucosa selected due to their high level in iodine as a mineral or an organic form and low levels of heavy metals. As a control we studied in a normal man the bioavailability of pure mineral iodine such as potassium iodide which was excellent i.e. 96.4% and of pure organic iodine such as monoiodotyrosine which was a little lower i.e. 80.0%. Iodine bioavailability from these two seaweeds was studied in nine normal subjects from Marseille (France) which is an iodine sufficient area based on a median urinary iodine level of 137 microg/day and innine normal subjects from Brussels (Belgium) who present a mild iodine deficiency with a value of 73 microg/day. The iodine bioavailability of Gracilaria verrucosa is better than for Laminaria hyperborea (101% versus 90% in Marseille, t=0.812, NS; 85% versus 61.5% in Brussels, t = 2.486, p = 0.024, S*). The urinary excretion of iodine is lower in Brussels than in Marseille for the same seaweed because part of the iodine is stored in the thyroid (101% versus 85% for Gracilaria verrucosa, t = 1.010, NS; 90% versus 61.5% for Laminaria hyperborea, t = 3.879, p= 0.001, S***).