Studies on the iodine concentration of milk have also been
undertaken in other countries over recent years.25,26 The general
conclusion in all these studies is that the iodine composition in milk
varies greatly from one sample to another, that changes in the
concentration have occurred over time and that this variation has
not usually been the result of a policy of regulating the iodine
concentration in milk. A few of the causes of this variation are
known and common to all the studies. The iodine concentration is
higher in winter milk samples than in summer milk
simples.19,20,24,25 This variationwas also found in our study, though
it was not so marked as that of other studies.24,27 Another variation
found in our study was the greater iodine concentration detected in
skimmed milk; this, too, has been seen elsewhere, though it was
not commented on in the results.27 Nevertheless, the most
important variations in the concentration of iodine in milk are
random, as shown in our study, with wide variation found within
the same brands, with ranges above 100 mg/L. Iodine in cow’s milk
comes from the iodine consumed by the animal in fodder, as well as
the contamination of products used for disinfection and sterilization.
9e11 The milk that can be bought in commercial establishments
in Spain is pooled from several dairy farms. Thus, any high
iodine concentrations in milk from one farm will be diluted by
lower concentrations in milk from other farms. The differences in
iodine administration in veterinary practice may also explain part
of this variation.24
Populations affected by iodine deficiency should be considered
as more sensitive to the adverse effects of iodine intake, such as
a higher risk of both hyper- and hypothyroidism in the event of
acute or chronic exposure to high doses of iodide.
Therefore, in Europe, the Scientific Committee on Food
proposed an upper limit of iodine intake in the healthy population
and the upper iodine levels in feed for dairy cows is also regulated
according to the recommendations of animal nutrition scientists.28
Reducing iodine to a maximum of 4 mg/kg complete feed for dairy
cows would result in a satisfactory margin of safety for the
consumption of milk.