Discussion and summary of exposure/intake

Generally, in Norway, iodine intake estimates are considered to be reliable as few food products have been iodized and drinking water contains only small amounts of iodine.

However, there are methodological concerns and limitations related to the various dietary survey methods for adults, adolescents and toddlers and infants.

Comparison of data from different dietary surveys

Norkost 3, Ungkost 3 and Småbarnskost 3/Spedkost 07 have all used different dietary assessment methods. Norkost 3 and Ungkost 3 have used recall and record methods that collect the food intake day by day, while FFQs were used in Småbarnskost 3/Spedkost-07.

The iodine exposure estimates for 1- and 2-year-olds are based on individual intakes whereas the exposure estimates for adults, 13-, 9- and 4-year-olds are based on a mixed models (MM) method. Modelling to correct for day to day variation could not be carried out for iodine intakes in 1- and 2-year-olds, since the underlying data are based on FFQ. Day-to-day variation is partially accounted for in the FFQ method, as the dietary intakes estimated from an FFQ reflect habitual intakes over a longer period of time.

The impact of a mixed model approach on the exposure estimates is typically a reduction in the tails, i.e. a narrower distribution of chronic intake, compared to OIMs or daily intakes.

Furthermore, a reduction in the mean intake is expected, as the daily intake distributions are skewed and an increase in the number of days will reduce the impact of rare days of very high intake (i.e. the upper tail).

VKM Report 2020: 05 143 The mean iodine intake estimates for 2-year-olds (Table 7.3.2-1) and non-breastfed 1-year-olds are higher than the mean iodine intake for 4-year-1-year-olds (Table 7.3.1-1), and it is therefore reasonable to assume that the estimated iodine intakes in the 2-year-olds are higher than the true intakes. Due to the relatively large proportion of underreporters of energy in adults and 13-year-old (16 and 33%, respectively), it is reasonable to assume that our estimated iodine intakes in adults and especially in the 13-year-olds are somewhat lower than true intakes. It should be noted that under- and overreporting of energy was not accounted for in the MM-modelling of the iodine exposure estimates.

The intake estimates and scenarios presented here in chapter 7 do not include intakes from food supplements. Scenarios including supplements (users only) are presented in

Appendix V.

It has recently been proposed that comparison of population intakes with recommended intakes will yield an overestimate of inadequacy as the recommended intake is set to cover almost all individuals (Allen et al., 2019). We have commented on whether mean and median intakes are below or above the recommended intakes, but this information is not used to evaluate the adequacy of the intake in the benefit and risk characterisation.

Current iodine intake

Iodine intakes in adults are higher in men than in women and increase with age for both sexes. Women of childbearing age have the lowest estimated intakes among adults, and 74% have intakes above the EAR. 13-year-old girls have the lowest intake, and only 62% of these girls have intakes above the EAR. All adults and 13-, 9- and 4- year-olds have intakes below the UL (presented in Table 7.3.1-1).

The estimates for 1- and 2- year-olds show that 92% of the 2-year-old boys and 91% of the girls have intakes above the EAR, and 65% of breastfed 1-year-olds and 92% of

non-breastfed have intakes above the EAR of 65 µg/day. The estimated iodine intake in the 95th percentile is 215 µg/day, slightly above the UL of 200 µg/day, and 8% of the 2-year-olds exceed the UL (presented in Table 7.3.2-1). However, excessive iodine intakes above the UL seem to be less frequent in the older age groups (from 4-years and older), and may

therefore be described as transient.

The scenarios

Scenarios (presented in Tables 7.4-3 – 7.4-14) were conducted to estimate what the iodine intake would be if household salt and salt used in bread were iodized up to 15, 20, 25 or 50 µg iodine per kg salt.

The model-based scenarios in adults and 13-, 9- and 4-year-olds show impact at increasing iodization levels and naturally more impact if both household salt and salt in bread was iodized. We have presented 12 scenario tables, three scenarios (household salt alone, salt in bread alone and both household salt and salt in bread) for four iodization levels (15, 20, 25

VKM Report 2020: 05 144 and 50 mg iodine per kg salt). The percentages of the population groups with intakes above the EAR increases with increasing iodization levels, but so does the percentages with intakes above UL. In the scenario with both household salt and salt in bread at level 25 µg iodine per kg salt at least 99% of all the subjects in these age groups have iodine intakes above EAR and in all age groups the percentage of subjects exceeding UL is ≤ 3%.

For 2-year-olds all scenarios lead to an increase in both the proportion of toddlers with estimated intakes above EAR and intakes above UL. As increasing iodization levels of both household salt and bread elevates the children with low iodine intake above the EAR, a larger portion will have intakes exceeding the UL. At the iodization scenarios with 25 or 50 mg iodine per kg salt, including iodization of household salt and salt in bread, the proportion of 2-year-olds expected to exceed the UL rises to 30-63%.

Supplement use and population groups at risk of low or high intakes

Scenarios including supplements (users only) are presented in Appendix V. Adult and adolescent iodine supplement users (regular supplements – not seaweed and kelp based supplements) are not at special risk of high intakes, even in the scenarios with increased iodization levels, compared to the general population. 2-year-old supplement users are at high risk of exceeding UL. Kelp-, tare- and seaweed-based supplements may contain significantly higher concentrations of iodine than regular iodine supplement users.

A total of 16% of the women and 11% of the men participating in Norkost 3 reported use of supplements containing iodine, with a mean iodine contribution of 95 and 117 µg/day, respectively. In Småbarnskost 3, 10% of the 2-year-olds reported use of iodine-containing supplements with a mean iodine contribution of 96 µg/day. In MoBa, 32-37% of the pregnant women reported use of iodine-containing supplement during the first half of pregnancy (Brantsaeter et al., 2013). The median amount of iodine contributed by supplements was 107 μg/day in iodine-supplement users (Brantsaeter et al., 2013).

Individuals omitting all foods of animal origin receive very little iodine through their diet.

Subjects with allergy to milk and/or fish-products and vegans are likely to have low iodine intakes. For persons with few iodine sources in the diet, the increase in iodine intake from increased iodization of salt and bread may be the same as for the lower percentiles (e.g. the 5th percentiles) in the scenarios in Tables 7.4-3 - 7.4-14. Vegans are recommended to use iodine-containing dietary supplements, and some vegans have iodine intakes above the UL due to use of a kelp-supplements.

Some ethnic minorities have been suggested to be at risk of low iodine intakes. However, a study on iodine status in women from the Oslo area, found no association between iodine status and ethnicity (Henjum et al., 2018a).

Effect of potential salt reduction on the scenario estimates for iodine

VKM Report 2020: 05 145 A uniform 30% reduction in average salt consumption implies a need for 43% increased iodization levels to achieve the same levels of daily iodine intake as given in the scenario Tables 7.4-3 -7.4-14 for all the age groups.

VKM Report 2020: 05 146