Objective: Auditory disturbances may be present in iodine deficient children. The aim of this study was to determine the effect of long-term iodine supplementation on auditory thresholds in iodine deficient children.
Design and methods: 70, 70 and 72 schoolchildren of an area of severe iodine deficiency were studied before intervention (1989), 3 yr after injection of 480 mg iodized oil (1992) and 7 yr after consumption of iodized salt (1999), respectively. Goiter was graded and serum T4, T3, TSH and thyroglobulin concentrations and urinary iodine levels were measured. Audiometry was performed with a pure tone audiometer.
Results: There was significant decrease in the prevalence and severity of goiter and serum TSH and thyroglobulin concentrations, and significant rise in serum T4 in 1992 and 1999, as compared to 1989. Before iodine supplementation, hearing was abnormal in 44% of schoolchildren, mean hearing threshold was 15.8 +/- 5.9 and in all children was >10 dB. Mean hearing threshold decreased to 10.2 +/- 4.6 and 10.0 +/- 5.9, 3 and 10 yr after intervention (p < 0.001). Forty seven and 62% of children had thresholds < 10 dB in 1992 and 1999, respectively. Hearing thresholds > 15 dB were detected in 46, 11 and 10% of schoolchildren in 1989, 1992 and 1999, respectively (p < 0.001).
Conclusion: Continuous iodine supplementation permanantly improves the auditory thresholds of iodine deficient children.