Stable and radioiodine concentrations in cow milk: dependence on iodine intake

For testing the potential use of stable iodine as a countermeasure to reduce radioiodine transfer to milk, concentrations of stable iodine and radioiodine in the milk of dairy cows fed different amounts of stable iodine were measured. The results indicated that, compared to a normal average stable iodine intake of about 20 mg d−1 for cows, low iodine dietary intake (<1.5 mg d−1) resulted in a reduced transfer of radioiodine to milk by 25%, varying stable iodine intakes in the range of 10–500 mg d−1 did have no significant effect; at stable iodine intake rates above 1000 mg I d−1, a reduction by a factor of approximately two was achieved. The high dietary iodine intakes – being about 100 times the normal iodine supply – required to reduce the radioiodine transfer significantly, will result in stable iodine concentrations in milk in excess of advised or legal limits for human consumption. Nevertheless, the provision of stable iodine via the milk pathway might be considered for emergency situations when stable iodine is used as a preventative measure for dose reduction to humans.