Iodine
For people without an existing thyroid condition, iodine is essential as it is required for the production of thyroxine. It is particularly important in women who are pregnant as it is needed to ensure the development of a baby's brain during pregnancy and early life.
Good sources of dietary iodine are eggs, milk and fish so anyone excluding these major food groups may need to consider taking a supplement containing iodine.
However, for people with an existing thyroid condition, iodine supplements or kelp (a type of seaweed rich in iodine) should be avoided. This is because they often contain excessive and/or variable amounts of iodine which can worsen existing thyroid conditions.
Read more about iodine and the thyroid