Iodine status in populations is assessed using urinary iodine concentration (UIC) measured in spot urine samples. The iodine intake is classified as deficient, sufficient, or excessive iodine based on the median UIC (mUIC). However, this approach has limitations, as it does not quantify the prevalence of individuals with habitually deficient or excess iodine intakes. The EAR cut-point method has the potential to quantify prevalence of iodine deficiency and excess. However, little is known about the effects of the inter- and intra-individual variance of UIC.

The aim of the study is to quantify the intra-individual variability in dietary iodine intake. The overall goal is to estimate the prevalence of iodine deficiency and excess in the study population and propose sample size recommendations for future iodine nutrition population studies. The results will provide evidence guiding international recommendations for iodine nutrition studies.

Inclusion Criteria:

• Non-pregnant
• Non-lactating
• Non-smoking
• Residence in Switzerland ≥12 months
• Generally healthy
• No family history of goiter
• No exposure to iodine containing contrast agents during the last 12 months - Informed consent given

Exclusion Criteria:

• Participant is not able to understand the study information or procedure, e.g. due to linguistic barriers

Healthy women of reproductive age and residents of Switzerland since at least 12 months