E-numbers / Other additives / E917
also: KIO3
A chemical compound once used to strengthen bread dough and add iodine to flour. Not permitted as a food additive in the UK or EU.
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Pork, Iodised Salt [Salt, Potassium Iodate], Dextrose, Spices, Pork Fat, Flavour Enhancer [Monosodium Glutamate, Disodium Inosinate, Disodium Guanylate], Preservative [Sodium Nitrite], Beechwood Smoke
Regular use in bread can push iodine intake well above recommended levels, which disrupts thyroid function.
94
of the 43,325 UK supermarket foods we checked declare E917 in their ingredients
That is 0.2%, counted by its code or its name.
Counted by NutraSafe from UK supermarket ingredient lists, September 2026. How we counted
Why it’s worth knowing. Regular use in bread can push iodine intake well above recommended levels, which disrupts thyroid function. People with thyroid conditions are particularly at risk from excess iodine. It is not on the UK list of approved food additives, so you will not normally see this E number on a UK label.
Potassium iodate is an inorganic salt of iodine and potassium. It is a white crystalline powder that acts as an oxidising agent and also releases iodine into food. It is distinct from potassium iodide, which is used in iodised table salt.
As a flour treatment agent it strengthens the gluten network in dough, improving the elasticity and volume of baked bread. It also delivers a dose of iodine to the finished product. The oxidising action tightens protein bonds in the dough during mixing.
Historically added to bread flour in some countries as a dough conditioner and iodine supplement. Not used in UK or EU food manufacturing. In countries where it is permitted, such as the United States, it may appear on bread labels as 'potassium iodate' or 'dough conditioner'.
Iodine is an essential nutrient, but too much of it can disturb the thyroid gland. The thyroid regulates metabolism by producing hormones that depend on iodine, but excess iodine can trigger both overactive and underactive thyroid conditions. People who already have thyroid disease are especially sensitive to high iodine loads.
JECFA concluded that the use of potassium iodate as a flour treatment agent was unacceptable because it could result in excessive iodine intake from bread alone.
Both insufficient and excess iodine intake are associated with thyroid disorders including hypothyroidism, hyperthyroidism and increased risk of thyroid cancer in epidemiological studies.
The European Union never authorised potassium iodate as a permitted food additive under its additives legislation, and the UK carried that position forward after leaving the EU. The core objection is that using it in staple foods like bread creates an unpredictable iodine intake on top of iodine from other dietary sources such as dairy and fish.
Potassium iodate does not appear in the UK FSA approved additives list or in EU Regulation 1333/2008 Annex II, meaning its use as a food additive is not permitted in the UK or EU.
People with thyroid conditions, including Hashimoto's thyroiditis, Graves' disease, or nodular thyroid disease, should avoid products from countries where this additive is permitted. It would appear on the label as 'potassium iodate' or 'dough conditioner'. In the UK and EU it should not be present in any food product.
The science on excess iodine from food additives is consistent rather than contested: iodine is a narrow-margin nutrient where too little and too much both cause thyroid harm. The JECFA assessment from 1965 has not been overturned and the EU has never authorised this additive. The dispute is not about whether excess iodine causes harm but about what intake levels bread could realistically deliver and for whom that would be a problem. UK shoppers buying food made and labelled in the UK will not encounter it.
E917 potassium iodate is not an authorised food additive in the UK. It does not appear on the UK FSA approved-additives list, so UK food manufacturers cannot use it.
Iodine is essential, but the quantity released by adding potassium iodate to bread dough is hard to control and can push daily iodine intake well above the recommended upper level, particularly for people who eat a lot of bread. UK dietary guidance addresses iodine deficiency through iodised salt and dairy sources rather than flour treatment.
No UK or EU food products should contain E917. In countries where it is permitted, such as the United States, it may be found in commercially produced bread and rolls as a flour improver.
Potassium iodate is an inorganic mineral salt with no animal-derived ingredients, so it is suitable for vegans by composition. However, since it is not permitted in UK or EU food, this question is largely academic for UK shoppers.
Last reviewed: 20 June 2026
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