E917 – Potassium iodate - Food additives database

Safety grading RED – UNSAFE

ADI: not allocated for potassium iodate as a flour-treatment agent. Instead of setting a normal Acceptable Daily Intake, the Joint FAO/WHO Expert Committee on Food Additives concluded that iodates should not be used for flour treatment, because adding a physiologically potent source of iodine to a staple food could push iodine intake too high. That judgment rested on older flour-treatment evaluations and toxicity work, including acute and subacute animal studies rather than a modern long-term NOAEL study (Webster et al., 1966; PMID 5956871; Bürgi, 2001; PMID 11396703).

E917 is graded RED – UNSAFE mainly for regulatory reasons. Potassium iodate is not on the EU Union list of approved food additives, so it is not an authorised EU additive for routine food use. In the United States it is still affirmed as Generally Recognized as Safe (GRAS) for bread manufacture at up to 0.0075% of the flour weight, but under this site’s rules, lack of approval in the EU is enough for a red grade.

The toxicology picture also supports caution. A major review concluded that small long-term iodate exposures from iodized salt probably carry low tissue-injury risk, but it also noted that genotoxicity and carcinogenicity data were scarce (Bürgi, 2001; PMID 11396703). A cell study did not find DNA damage up to 10 mM in the assays used (Poul et al., 2004; PMID 14667467). However, human overdose reports show severe retinal injury, sometimes with lasting outer retinal atrophy, after large exposures (Singalavanija et al., 2000; PMID 10950416; Reddy et al., 2018; PMID 30083392; Bernstein, 2025; PMID 39999390). Modern endocrine reviews also confirm that excess iodine can trigger hypo- or hyperthyroidism in susceptible people, including those with thyroid disease, pregnancy-related vulnerability, infancy, or kidney problems (Karbownik-Lewińska et al., 2022; PMID 35726078). The red grade does not mean a trace amount would automatically harm everyone. It means E917 is an outdated flour improver with a poor EU regulatory position and safer alternatives available.

Should You Avoid E917?

Yes. In the EU, most consumers are unlikely to see E917 in legal everyday foods because it is not an approved additive. Still, it can appear in imported bakery improvers, older technical documents, or products from markets where potassium iodate has historically been used. Avoiding it is sensible, especially if you already get extra iodine from supplements, seaweed products, iodized salt, or thyroid medication.

Common Uses

Bread flour improver, where it was used to strengthen dough.
Dough conditioner in industrial bread and rolls.
Oxidizing flour treatment agent to improve gas retention and loaf volume.
Bakery premixes and bread improver blends in markets that still permit it.
In some countries, potassium iodate is used to iodize salt, although that is a nutrient-fortification use rather than its classic E917 additive role.

Common names / Synonyms

Potassium iodate
Iodic acid, potassium salt
Potassium iodine oxide
KIO3
INS 917
Flour treatment agent
Dough strengthener

What is it?

Potassium iodate is an inorganic iodine compound with the formula KIO3. It is a white crystalline oxidizing salt. In baking technology, its role was to make dough stronger by oxidizing reactive groups in gluten-related proteins, which helps create a tighter and more elastic dough network. That can improve dough handling, gas retention, and loaf volume in weaker flours.

What makes potassium iodate unusual is that it is not nutritionally inert. After ingestion, iodate is rapidly reduced in the body to iodide, the biologically useful form of iodine. So E917 is not just a processing chemical. It can also add to total iodine intake. That matters because bread is a staple food eaten regularly, so even a modest contribution from flour treatment can be more important than it first appears.

Industrially, potassium iodate can be prepared by reacting iodine with potassium hydroxide and then isolating the iodate salt. It has also been used in salt-iodization programs because iodate is often more stable than iodide during storage. That stability is useful in fortification, but it does not automatically make the compound a good choice as a bread additive. Modern baking has better accepted alternatives, such as ascorbic acid and enzyme-based improvers, so E917 now looks more like a legacy additive than a necessary one.

Where it’s allowed (EU vs US)

As of March 2026, E917 is not on the EU Union list of approved food additives, so it is not an authorised EU additive for ordinary food use. In the United States, potassium iodate remains affirmed as Generally Recognized as Safe for bread manufacture under 21 CFR 184.1635, with a maximum of 0.0075% based on flour weight. Separate national rules may still allow potassium iodate as an iodine fortificant in salt, which is a different use from its older bakery-improver role.

E917 – Potassium iodate