Variation in the iodine content of milk, dairy products, and eggs and the implication for UK iodine intake; studies at the farm, retail, and populatio

Iodine deficiency is common in some UK groups, such as in women of childbearing age. This is a public-health concern as even mild-to-moderate deficiency during pregnancy is associated with lower IQ in children. In the UK, and many countries, milk, dairy products, and eggs are the main dietary sources of iodine, together contributing over 40% of total iodine intake in UK adults, and up to 68% in children (National Diet & Nutrition Survey data, 2021).
We know that there is considerable variation in the iodine concentration in milk - for example iodine concentration varies by season, with lower iodine in summer milk. Components of cattle feed, for example white clover, may act as goitrogens and reduce the transfer of iodine into milk, although data are lacking to confirm this effect. While there is a known interaction between agricultural practice and the iodine content of milk, there are no data on its effects on the iodine content of other dairy products (e.g. yoghurt) or eggs.
Estimating the optimum iodine concentration of milk, dairy products, and eggs is key to ensuring adequate iodine intake in the population. This is especially true in the UK as there is no policy to fortify salt with iodine, unlike in many other countries where iodised salt is an important source of iodine.