Mild iodine deficiency is associated with elevated hearing thresholds in children in Benin

Objective: Elevated hearing thresholds have been demonstrated in population s afflicted by endemic cretinism as a result of severe iodine deficiency. H owever, data on the effects of less severe iodine deficiency on hearing thr esholds in apparently normal children are scant. This study addresses the q uestion whether there is a relationship among iodine variables, hearing and mental performance in a mildly iodine-deficient population. Design: A randomized, placebo-controlled intervention trial with an observa tion period of 11 months. Setting: An iodine-deficient area in northern Benin. Subjects: A total of 197 school children, aged 7 - 11 y. Interventions: A total of 97 children received an oral dose of iodized oil, containing 540 mg I, while 100 children received a placebo. About 3-4 mont hs after supplementation, the whole population began to have access to iodi zed salt. Non-verbal mental tests were administered and biochemical indicat ors (thyrotropin, free thyroxine, thyroglobulin and urinary iodine) were me asured at the beginning and the end of the study. Hearing was measured at t he end of the study in both ears by pure-tone audiometry at seven frequenci es. Results: In this mildly iodine-deficient child population children with hig her serum thyroglobulin concentrations had significantly higher hearing thr esholds in the higher frequency range (greater than or equal to 2000 Hz) th an children with lower serum thyroglobulin concentration. Moreover children with lower hearing thresholds performed significantly better on the mental tests used. Conclusions: Even when iodine deficiency is 'mild', promotion of adequate i odine intake through salt iodization programs and other means remains cruci al. Sponsorship: Nestle Foundation, Lausanne, Switzerland; Wageningen Unive rsity, Wageningen, The Netherlands. Descriptors: iodine deficiency; hearing thresholds; schoolchildren; Benin.