A novel concept to derive iodine status of human populations from frequency distribution properties of a hair iodine concentration

Today, human iodine deficiency is next to iron the most common nutritional deficiency in developed European and underdeveloped third world countries, respectively. A current biological indicator of iodine status is urinary iodine that reflects the very recent iodine exposure, whereas some long term indicator of iodine status remains to be identified. We analyzed hair iodine in a prospective, observational, cross-sectional, and exploratory study involving 870 apparently healthy Croatians (270 men and 600 women). Hair iodine was analyzed with the inductively coupled plasma mass spectrometry (ICP MS). Population (n870) hair iodine (IH) respective median was 0.499 μg g−1 (0.482 and 0.508 μg g−1) for men and women, respectively, suggesting no sex related difference. We studied the hair iodine uptake by the logistic sigmoid saturation curve of the median derivatives to assess iodine deficiency, adequacy and excess. We estimated the overt iodine deficiency to occur when hair iodine concentration is below 0.15 μg g−1. Then there was a saturation range interval of about 0.15–2.0 μg g−1 (r2 = 0.994). Eventually, the sigmoid curve became saturated at about 2.0 μg g−1 and upward, suggesting excessive iodine exposure. Hair appears to be a valuable and robust long term biological indicator tissue for assessing the iodine body status. We propose adequate iodine status to correspond with the hair iodine (IH) uptake saturation of 0.565–0.739 μg g−1 (55–65%).