A database of results for the iodine content of foods and diets was prepared for a DFID funded project looking at \"Environmental Controls in Iodine Deficiency Disorders\". It was populated with citations from the literature and contains 732 records. On the basis of these data, the geometric mean result for the iodine content of foods is 87 µg/kg, from 494 citations.
Using classifications based on food type the following order for levels of iodine is determined:
Marine fish (1455.9 µg/kg) > Freshwater fish (102.8 µg/kg) > Leafy vegetables (88.8 µg/kg) > Dairy (83.9 µg/kg) > Other vegetables (80.1 µg/kg) > Meat (68.4 µg/kg) > Cereals (56.0 µg/kg) > Fresh fruit (30.6 µg/kg) > Bread (17.0 µg/kg) > Water (6.4 µg/l)
(The figure in brackets represents the geometric mean value for each group)
The results show that in general grain crops are poorer sources of iodine than vegetables and that there is some equivocal evidence to suggest that leafy vegetables contain higher iodine concentrations than other vegetables but fish and seaweed are by far the greatest natural sources of iodine in foodstuffs.
The geometric mean result for the average daily dietary intake is 161 µg/day, based on 84 citations. It is noted that vegetarian and vegan diets often do not meet the recommended adult daily intake of 150 µgI/day due to the lack of dairy, meat and fish components. Results also show that Japanese, USA and Canadian dietary intakes are higher than other countries.
Intake depends not only on the iodine content of the food but also on the composition of the diet. Results show that food accounts for over 90% of human iodine exposure in most circumstances with water and air providing minimal inputs. However, in subsistence populations drinking highiodine groundwaters, water can contribute more than 20% of the dietary intake. Results of dietary studies show the following general order of percentage daily iodine intake from the main food groups in Western Countries:
Dairy (50%) > Cereals (20%) > Fish (9%) > Meat (8%) > Vegetables (7%) > Sweets (5%) > Fruits (1%)
The majority of iodine in Western diets comes from adventitious sources such as iodophors in the dairy industry, red food colouring and improvers in cereals, bread, meat and sweets. Removing these components to equate to a developing country diet where people are often dependant on staple grain foodstuffs such as rice shows that intakes fall below 100 µg/day. It is concluded that without adventitious sources of iodine or a marine foods component, most diets would fail to provide the recommended daily intake of 150 µg/day.
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