Iodised salt for preventing iodine deficiency disorders

Wu T, Liu GJ, Li P, Clar C

Published Online:

January 21, 2009

Iodine deficiency causes mental retardation in children as well as enlarged thyroid glands (goitre) and deficiencies in thyroid hormones in people of all ages. It still exists in large parts of the world. This review looked at studies of iodised salt in the diet that included a comparison group. Six studies, most of them in children but some also in adults, were included. Iodine in the urine increased in all but one studies, but there was some concern that small children did not eat enough salt to achieve adequate iodine status. Some studies, but not all, also showed a reduction in the enlargement of the thyroid gland (goitre) that can accompany lack of iodine in the diet. Adverse effects were not reported, but these may not have been studied adequately. More high quality long term studies measuring outcomes related to child development, to deaths associated with iodine-deficiency and to adverse effects are needed.

Abstract (click to read)

Background:

Iodine deficiency is the main cause for 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 iodised salt in comparison with other forms of iodine supplementation or placebo in the prevention of iodine deficiency disorders.

Search strategy:

We searched The Cochrane Library, MEDLINE, the Register of Chinese trials developed by the Chinese Cochrane Centre, and the Chinese Med Database, China National knowledge Infrastructure, and searched reference lists, databases of ongoing trials and the Internet.

Selection criteria:

We included prospective controlled studies of iodised salt versus other forms of iodine supplementation or placebo in people living in areas of iodine deficiency. Studies reported mainly goitre rates and urinary iodine excretion as outcome measures.

Data collection and analysis:

The initial data selection and quality assessment of trials was done independently by two reviewers. Subsequently, after the scope of the review was slightly widened from including only randomised controlled trials to including non-randomised prospective comparative studies, a third reviewer repeated the trials selection and quality assessment. 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:

We found six prospective controlled trials relating to our question. Four of these were described as randomised controlled trials, one was a prospective controlled trial that did not specify allocation to comparison groups, and one was a repeated cross-sectional study comparing different interventions. Comparison interventions included non-iodised salt, iodised water, iodised oil, and salt iodisation with potassium iodide versus potassium iodate. Numbers of participants in the trials ranged from 35 to 334; over 20,000 people were included in the cross-sectional study. Three studies were in children only, two investigated both groups of children and adults and one investigated pregnant women. There was a tendency towards goitre reduction with iodised salt, although this was not significant in all studies. There was also an improved iodine status in most studies (except in small children in one of the studies), although urinary iodine excretion did not always reach the levels recommended by the WHO. None of the studies observed any adverse effects of iodised salt.

Authors' conclusions:

The results suggest that iodised salt is an effective means of improving iodine status. No conclusions can be made about improvements in other, more patient-oriented outcomes, such as physical and mental development in children and mortality. None of the studies specifically investigated development of iodine-induced hyperthyroidism, which can be easily overlooked if just assessed on the basis of symptoms. High quality controlled studies investigating relevant long term outcome measures are needed to address questions of dosage and best means of iodine supplementation in different population groups and settings.

This record should be cited as:

Wu T, Liu GJ, Li P, Clar C. Iodised salt for preventing iodine deficiency disorders. Cochrane Database of Systematic Reviews 2002, Issue 3. Art. No.: CD003204. DOI: 10.1002/14651858.CD003204

Assessed as up to date:

August 31, 2004

Health topics:

Child health > Endocrine & metabolic > Thyroid disorders

Endocrine & metabolic > Thyroid disorders

Cochrane Summaries

Independent high-quality evidence for health care decision making

Iodised salt for preventing iodine deficiency disorders

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