In brief
The thyroid uses iodine from food to make the hormones thyroxine (T4) and tri-iodothyronine (T3). The pituitary gland sets the pace with TSH.
- Since 2009, manufactured bread in Australia has been made with iodised salt, according to healthdirect.
- Not getting enough iodine is one cause of an underactive thyroid.
- TSH is the only thyroid test covered by Medicare if you do not have a history of thyroid problems.
How it works
The thyroid needs iodine to make its hormones, and people need about 150 micrograms a day, according to the Better Health Channel. It makes mostly T4, while T3 is more active but made in smaller amounts. Your thyroid gland also needs selenium to make hormones.
The pituitary gland releases thyroid stimulating hormone (TSH), which prompts the thyroid to release more T4 and T3. When T4 is high, the pituitary makes less TSH, and when it is low, it makes more. Doctors check TSH first, and test free T4 or free T3 if TSH is abnormal.
Connections
3 connections on the map. Select a topic to read its page.
Thyroid hormone production needs
Your body needs iodine to make thyroid hormones.
Sources: healthdirect Australia, Foods high in iodine; NIH Office of Dietary Supplements, Iodine fact sheet for consumers
Your thyroid gland needs selenium to produce hormones.
Source: NIH Office of Dietary Supplements, Selenium fact sheet for consumers
Thyroid hormone production is part of
The thyroid uses iodine from your diet to make thyroid hormones.
Sources: Pathology Tests Explained, Thyroid function tests; Better Health Channel (Victorian Government), Thyroid gland
Lab tests
Sources
- Thyroid gland
- Thyroid function tests
- Thyroid stimulating hormone (TSH)
- Foods high in iodine
- Selenium fact sheet for consumers
- Hypothyroidism (underactive thyroid)
Each connection above names its own source. See every source AskBioMap uses.
Summarised from the Better Health Channel, Pathology Tests Explained, healthdirect and the NIH Office of Dietary Supplements. Sources read on 13, 16 and 19 October 2026. General education only, not medical advice. Spotted a mistake? Please tell us through the HuBu-Intel contact page.