A recent study by the FSA into levels of Iodine in common food, shows that Sheep milk contains very high levels.

Iodine is an essential nutrient required for the synthesis of thyroid hormones. The most well known iodine deficiency disorder (IDD) is enlargement of the thyroid gland (goitre).
Iodine deficiency can also result in a wide range of mental, psychomotor and growth abnormalities, as well as increased infant mortality.

Although now rare in the UK, iodine deficiency is still recognised as an international health problem. To guide against iodine deficiency, the UK Department of Health’s Committee on Medical Aspects of Food Policy (COMA) has recommended a Reference Nutrient Intake (RNI) of 0.14 mg/day for adults and 0.05-0.14 mg/day for children. (The RNI is defined as an amount of a nutrient that is sufficient, or more than sufficient, for about 97 per cent of people in a group. If average intake of a group is at the RNI, then the risk of deficiency in the group is very small.) In comparison, the upper bound average iodine intake for the general UK population estimated in the COMA report was 0.25 mg/day and that estimated from the 1997 Total Diet Study was 0.24 mg/day.
The FSA regularly monitors the concentrations of metals and other elements in food.

Previous multi-element Total Diet Studies (which are representative of the average UK diet) have shown that concentrations of metals and other elements in food do not present significant risks to the general UK population.
However, estimates of dietary intakes for the general population cannot be easily or accurately extended to infants, as infants consume a diet that is different in many ways from that of adults or of children old enough to eat conventional adult foods. As infants grow and develop very rapidly in their first year of life, their energy requirements and food consumption are on average higher relative to their body weight than that of adults and older children. This means that infants can have dietary exposures to chemicals present in food relatively higher than those for other age groups when expressed on a body weight basis.
In addition, infants’ diets are made up of a more restricted range of foods, particularly before and in the early stages of weaning when the diet is made up entirely or largely of breast milk and/or commercial formulae.

The results of the latest survey for iodine in UK foods are described below.

A summary of the mean concentration of iodine in each food type is given in Table 1 of the report.
Goats’ and sheep’s milk and their products are listed separately from cows’ milk. The number of non-cow milk-based dairy products analysed was limited, so the data may not be representative for this food group. Nevertheless, goat and sheep milk samples seem to show higher concentrations of iodine than cows’ milk. Results are expressed as upper bound, which means that where individual sample analyses were less than the limit of detection, the result is expressed as equal to the limit of detection which does not result in overestimation. A graphical presentation of the comparison of summer and winter sample is provided in Annex 1. Details of individual results are given in Annex 2.

The results are discussed below and compared with data from previous studies and recommended guidelines. Exposure calculations were carried out for comparison with the Provisional Maximum Tolerable Daily Intake (PMTDI) of 0.017 mg/kg bodyweight/day recommended by the Joint FAO/WHO Expert Committee on Food Additives (JECFA).

Iodine is present naturally in milk, but concentrations can be influenced by its presence in animal feed and/or from hygiene products used in the dairy industry. Iodine content of milk typically varies seasonally, however, the results of this survey show high concentrations in both the summer and winter samples. The highest concentration found in a winter sample of sheeps’ milk was 3.6 mg/kg and for summer, the highest concentration in sheeps’ milk was 4.6 mg/kg. However looking at the raw data, it does appear that there is a trend to suggest iodine levels are consistently lower in summer than winter. Similar trends are not seen for iodine concentrations in eggs. The seasonal variation reported in previous studies was considered to result from the greater use of compound feedingstuffs during the winter months. Iodine may be naturally present in the ingredients used in animal feedstuffs or may be added via feed supplements. Iodine is included in compound feedingstuffs to protect animal health as well as providing a source of iodine in human diets. The supplementation of animal feedingstuffs with iodine is controlled by legislation in the UK with a maximum permitted level of 10 mg/kg for dairy cattle.

Iodine may also occur in milk as a result of the use of iodophors as cow teat sterilants and equipment sanitizers in dairies.

All samples of cows’ milk in this survey contained low concentrations of iodine, with a range of 0.30 – 1.00 mg/kg. Goat and sheep milk samples contained slightly elevated levels of iodine above the level of detection, the highest levels of iodine found being 1.3 mg/kg in a sample of goats’ milk and 4.6 mg/kg in a sample of sheep’s milk. Although goat and sheep milk samples were not analysed for iodine in the MAFF 2000 iodine in milk survey, levels found in this survey are in line with those found in the composite samples of the 1997 Total Diet Study10. One sample of seaweed contained a very elevated level of iodine, at 2,400 mg/kg above the level of detection. The manufacturer of this sample is based in Northern Ireland and the FSA Northern Ireland office informed the relevant Local Authority, which has arranged to take additional samples when the product is next in season, in order to carry out further analysis.

The full paper can be seen on the Food Standards Agency website (click here) or download the pdf