Background: Iodine deficiency is the main cause of potentially preventable mental retardation in childhood, as well as causing goitre and hypothyroidism in people of all ages. It is still prevalent in large parts of the world.
Objectives: To assess the effects of iodine supplementation overall, and of different forms and dosages of iodine supplementation separately, in the prevention of iodine deficiency disorders in children.
Search strategy: The Cochrane Library, MEDLINE, EMBASE and reference lists, databases of ongoing trials and the Internet were searched. Date of latest search: October 2003.
Selection criteria: We included randomised controlled trials and prospective controlled trials not using randomisation of iodine supplementation in children living in areas of iodine deficiency.
Data collection and analysis: Two reviewers did the initial data selection and quality assessment of trials independently. As the studies identified were not sufficiently similar and not of sufficient quality, we did not do a meta-analysis but summarised the data in a narrative format.
Main results: Twenty-six prospective controlled trials were related to our question, assessing a total of 29613 children. Twenty of them were classified as being of low quality, six of moderate quality. Most studies used iodised oil as a supplement, but other supplements were also used. The intervention groups were compared to a non-supplemented control group, different doses or different forms of iodine supplementation. There was a clear tendency towards goitre reduction with iodine supplementation; this was significant in several studies. Significant differences in physical development were not seen, except in one study. Results for differences in cognitive and psychomotor measures were mixed, with only few studies showing a positive intervention effect. One study suggested that infant mortality was lowered after iodine supplementation. Most studies showed a significant increase in urinary iodine excretion and levels recommended by the WHO were reached in most cases after supplementation. Thyroid-stimulating hormone (TSH) levels were significantly reduced in one study. In 1.8% of the children investigated, adverse effects were found, most of them were minor and transient.
Reviewers' conclusions: Despite most of the included studies being of low quality, the results suggest that iodine supplementation, especially iodised oil, is an effective means of decreasing goitre rates and improving iodine status in children. Indications of positive effects on physical and mental development and mortality were seen, although results were not always significant. Adverse effects were generally minor and transient. Insufficient evidence was available on non-oil supplements. High quality controlled studies investigating relevant long term outcome measures are needed to address the question of the best form of iodine supplementation in different population groups and settings.