Iodine is a trace element involved in the synthesis of thyroid hormones. Find out about its importance to the body, the needs of the population and foods containing iodine.
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Updated on 21/03/2019
Functions, food sources and nutritional requirements
Definition, functions and roles
Iodine is a trace element involved in the synthesis of thyroid hormones. The secretion of these hormones begins early in foetal life and participates in the vital functions of the body, especially the neurological development of the foetus and newborn child.
Iodine requirements vary according to age, sex and physiological condition. Iodine intake is particularly critical for the pregnant woman and her unborn child, as well as during breastfeeding.
Composition of foods containing iodine
As part of a public health measure, table salt in France is used as a means of iodine fortification(1860 μg/100 g compared with 1.8 μg/100 g for non-iodised salt).
Besides this fortified salt, the foods richest in iodine are mainly marine products: fish, crustaceans and molluscs that contain up to 400 µg/100 g.
Seaweed is also rich in iodine but its concentration is highly variable.
Eggs, dairy products and cereals are also important food sources of iodine.
Population reference intakes (PRIs)
The population reference intake (PRI) for iodine in adults is 150 µg/d. During pregnancy, the iodine requirement is higher, and remains so when the mother breastfeeds (the PRI increases from 150 to 200 µg/d).
The reference intake is 80 µg/d for children aged 1-3 years, 90 µg/d for children aged 4-6 years and 120 µg/d for children aged 7-9 years, and then from the age of 10 it is 150 µg/d.
The European Food Safety Authority (EFSA) has also established a tolerable upper intake level for iodine of 600 µg per day for adults and adjusted for each population age group.
In addition, French regulations (the Ministerial Order of 9 May 2006) have laid down a maximum daily dose of iodine in food supplements of 150 µg.
Risks associated with deficiency or excess intake
Regular excessive intake of iodine can cause thyroid dysfunctions as well as certain adverse effects, particularly cardiac or renal.
Conversely, iodine deficiency can cause mental and psychomotor disorders. Indeed, insufficient iodine intakes can lead to the development of goitre (an increase in the volume of the thyroid gland) as well as serious impairment or retardation in a child's mental, neural and intellectual development. Even a slight iodine deficiency before pregnancy (urine iodine levels < 100 µg/L) can have harmful effects on foetal thyroid development and irreversibly affect foetal neurological development.
Studies carried out in France since 1985 show that the iodine requirements of children are covered or even exceeded in the youngest children, who are high consumers of milk. Many European surveys nevertheless underline the insufficient intakes in a large proportion of the population aged over 10 years. According to the INCA2 study, women of childbearing age have inadequate iodine intakes.
Nutritional impact of introducing iodine compounds into food products
In order to increase daily intake, universal iodine fortification of table salt has been recommended by the international health authorities (WHO, UNICEF). Salt iodisation helps to improve the iodine status of the population, but must also be consistent with dietary recommendations to reduce salt intake, due to both the consumer salting dishes at home, and salt being added to products by the food industry.
In France, salt iodisation is currently voluntary and not mandatory and only table salt can be iodised. In its 2005 report, the Agency expressed reservations about systematically using iodised salt in processed foods, as this would expose the population to the risk of exceeding the upper intake levels for iodine (especially among young children). This fortification is not currently authorised.
In the conclusions of its report, ANSES identified the most appropriate means to compensate for insufficient iodine intake in a part of the population, specifically the fortification of certain foods consumed by people aged 10 years and over. To ensure that high consumers, especially young children, do not exceed the upper intake levels for iodine, the Agency stated that any proposal for a new food vector for iodine that aimed to improve iodine intakes in the general population, can only be applied after an initial reduction of 15-20% in iodine concentrations in dairy products. This recommendation stems from the fact that milk produced in winter has an iodine content about 20% higher than that of milk produced in summer.
Considering this prior requirement, the Agency recommended that bakery products be chosen as the food for fortification with iodine (i.e. bread, rusks, croissant-like pastries) at a level of 20 µg of iodine/100 g. These everyday consumer products are suitable fortification vectors, both in technological and consumer acceptability terms. Such fortification would lead to an average decrease of 50% in the proportion of adults with very low intakes.