Abstract
Iodine, through the thyroid hormones, is required for the development of the auditory cortex
and cochlea (the sensory organ for hearing). Deafness is a well-documented feature of endemic
cretinism resulting from severe iodine deficiency. However, the range of effects of suboptimal
iodine intake during auditory development on the hearing ability of children is less clear. We
therefore aimed to systematically review the evidence for the association between iodine
exposure (i.e., intake/status/supplementation) during development (i.e., pregnancy and/or
childhood) and hearing outcomes in children. We searched PubMed and Embase and identified
330 studies, of which 13 were included in this review. Only three of the 13 studies were of low
risk of bias or of good quality, this therefore limited our ability to draw firm conclusions. Nine
of the studies (69%) were in children (one RCT, two non-RCT interventions and six crosssectional studies) and four (31%) were in pregnant women (one RCT, one cohort study and
two case reports). The RCT of iodine supplementation in mildly iodine-deficient pregnant
women found no effect on offspring hearing thresholds. However, hearing was a secondary
outcome of the trial and not all women were from an iodine-deficient area. Iodine
supplementation of severely iodine-deficient children (in both non-RCT interventions) resulted
in improved hearing thresholds. Five of six cross-sectional studies (83%) found that higher
iodine status in children was associated with better hearing. The current evidence base for the
association between iodine status and hearing outcomes is limited and further good-quality
research on this topic is needed.