Urinary iodine measures iodine concentration in a random urine sample and reflects recent dietary iodine intake over the preceding days, as the kidneys excrete approximately 90% of ingested iodine. Iodine is an essential mineral required for the synthesis of thyroid hormones (T3 and T4), which regulate metabolism, growth, and development. The WHO classifies urinary iodine as the best population-level indicator of iodine status.
Australia has mild-to-moderate iodine insufficiency in some population groups, and iodine is added to bread (through the mandatory use of iodised salt in bread making) to address this. Adequate iodine is especially critical during pregnancy and early life, when thyroid hormone is essential for foetal brain development. Iodine deficiency during pregnancy remains a leading preventable cause of intellectual disability worldwide.
FAQs
How reliable is a random urine iodine test?
A single random urine iodine is variable because of fluid intake effects on urine concentration. It is best used as a population screening tool or a rough individual indicator. A urinary iodine-to-creatinine ratio corrects for dilution effects and is more reliable for individual assessment.
Who is at highest risk of iodine deficiency in Australia?
Pregnant and breastfeeding women have the highest requirements and are most at risk. Vegans, people avoiding dairy and bread, and those on strict low-salt diets are also at higher risk. Routine iodine supplementation is recommended during pregnancy and breastfeeding.
Can too much iodine be harmful?
Yes. Excess iodine from high-dose supplements or kelp products can cause both hypothyroidism (blocking thyroid hormone synthesis) and hyperthyroidism (triggering excess production in predisposed thyroid glands). People with pre-existing thyroid conditions are particularly susceptible.
Does iodised salt provide enough iodine?
Using iodised salt in cooking provides a useful iodine contribution. However, most salt consumed by Australians is from processed foods that use non-iodised salt. Dairy and seafood are more reliable everyday iodine sources.
