In this project, the investigators propose an intervention design testing the efficacy of a food reformulated with seaweed as an ingredient in meal, capsules against placebo and no intervention controls. The randomised control trial (supplementation) will last 24 weeks. The aim is to study the effect of the food matrix on variables associated with iodine nutrition: iodine status and thyroid function.

This study is a randomized, double-blind, placebo-controlled trial conducted in Glasgow, United Kingdom. Inclusion criteria are as follows: healthy premenopausal women aged 18 - 60 years who would remain a resident in Glasgow for 24 weeks; who were self-reported low iodine consumers consuming milk less than once per day and non-oily fish less than once per week. Those with a history of thyroid dysfunction, taking medications other than the contraceptive pill or smoking, as well as pregnant or lactating women and those planning to conceive, were excluded. Those taking dietary supplements containing iodine would also excluded and there was no restriction related to body mass index (BMI).

Participants are recruited via social media and advertisements displayed around the Greater Glasgow area. Interested parties are screened and, if eligible, invited to a 30-minute appointment at which participants were randomly assigned through a web-based randomisation service to one of four groups after consent is obtained; reformulated pizza, control pizza, iodine capsules, or placebo capsules. During this initial meeting anthropometric measurements, blood pressure and a venous blood sample are collected, and participants are also asked to complete a sociodemographic questionnaire and an iodine specific food frequency questionnaire (FFQ). Participants are provided with instructions and equipment to record a 3-day estimated food diary and to collect 12 spot urine samples at different times of day over 2-7 days. Upon returning the spot urine samples, participants were given either the pizzas or supplements to begin the intervention. Participants are asked to consume one pizza or supplement three times a week for 24 weeks. Participants are asked to collect a further 10-12 sample spot urine samples at week 2 of the intervention. Participants are asked to attend another 30-minute appointment at 12 and 24 weeks in which baseline measurements are repeated along with a change to diet questionnaire.

Inclusion Criteria:

• self-reported healthy women
• aged 18 to 60
• pre-menopausal
• with no history of thyroid dysfunction
• without any known allergic reactions to foods
• not on medication that impact on absorption of nutrients from the gut
• not currently taking dietary / multivitamin supplements (must have discontinued usage 2 weeks prior the start of the study)

Exclusion Criteria:

• pregnancy
• lactation
• habitual consumption of seaweed-based products (>once per week), milk (>once per day), sea fish, non-oily, e.g. cod (>once per week)
• veganism (as food products contains cheese)
• Involvement in another research study where diet is restricted, modified, or dietary habits are studied.
• women who have reached menopause.

Masking of pizzas was achieved by the use of pizzas with identical appearance and taste.

Iodine and control supplements were also identical in appearance. Both pizzas and supplements were provided to investigators already masked. Pizzas labelled X and Y. Supplements labelled A and B