Iodine
Definition
Iodine was one of the first trace elements to be identified as essential. It is an essential part of thyroid hormones that regulate normal growth and metabolism. Iodine plays a role in physical and mental development and adequate iodine intakes are important for young children and women of child-bearing age (Gibson 2005; WHO/UNICEF/ICCIDD 2007; WHO 2013; NHMRC 2013).
Iodine deficiency can lead to a range of conditions, including goitres, hypothyroidism, impaired development and in pregnant women, major impacts on foetal development (WHO/UNICEF/ICCIDD 2007; NHMRC 2013).
In Australia, legislation mandating the use of iodised salt in bread manufacturing (excluding organic bread) was introduced in 2009. Biomedical measurement of iodine levels in the population were used to monitor and report on the effectiveness of this standard (AIHW 2011a, b, 2016). The World Health Organization (WHO) recommends monitoring iodine status over time and, if necessary, adjusting the concentration of iodine in salt available for sale, particularly in countries that have strategies to reduce the sodium/salt content of the food supply (WHO 2022).
Laboratory test information, including analysis methods and machines used to measure iodine, is available from the Downloads page.
Methodology
To enable population-level analysis, iodine tests were conducted on urine samples from persons aged 5 years and over. Fasting was not required for this test.
Iodine levels were measured at the Sullivan Nicolaides Pathology laboratory by the Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) method. The iodine test measures the concentration of iodine in the urine that has been excreted from the body, at the time of the test (spot sample), expressed as μg/L. Spot urine samples are not a sufficient measure for individual status; however, these results can be used to assess the population iodine status (Gibson 2005; WHO/UNICEF/ ICCIDD 2007; WHO 2013).
Prior to use of the ICP-MS method, most studies used methods of analysis based on the manual spectrophotometric measurement of the Sandell–Kolthoff reduction reaction catalysed by iodine using different oxidising reagents in the initial digestion step (Jooste and Strydom 2010). The WHO and the International Council for Control of Iodine Deficiency Disorders (ICCIDD) determined a set of cut-offs for median urinary iodine concentration (UIC) using these methods to define if a population was iodine deficient (WHO/UNICEF/ICCIDD 2007; WHO 2013), outlined in the table below.
No cut-offs have been developed specifically for the new ICP-MS method. However, research studies indicate that within ranges of UIC 0 – <600 μg/L, the results from the ICP-MS and methods using the Sandell–Kolthoff reaction are comparable (Caldwell et al. 2003; Li et al. 2021). Therefore, the WHO cut-offs for median UIC were applied to the ICP-MS results in the to determine iodine deficiency for the Australian population (RCPA 2023).
| Target population group | Median UIC (μg/L) | Iodine intake | Iodine status |
|---|---|---|---|
School-age children (6 years or older)(a)
| <20 | Insufficient | Severe iodine deficiency |
| 20–49 | Insufficient | Moderate iodine deficiency | |
| 50–99 | Insufficient | Mild iodine deficiency | |
| 100–199 | Adequate | Adequate iodine nutrition | |
| 200–299 | Above requirements | May pose a slight risk of more than adequate iodine intake in these populations | |
| ≥300 | Excessive(b) | Risk of adverse health consequences (iodine-induced hyperthyroidism, autoimmune thyroid disease) | |
| Pregnant women | <150 | Insufficient | As above |
| 150–249 | Insufficient | ||
| 250–499 | Adequate | ||
| ≥500 | Excessive(b) | ||
| Lactating women(c) and children <2 years old | <100 | Insufficient | As above |
| ≥100 | Adequate |
a. Applies to adults, but not to pregnant and lactating women.
b. The term “excessive” means in excess of the amount required to prevent and control iodine deficiency.
c. Although lactating women have the same requirement as pregnant women, the median urinary iodine is lower because iodine is excreted in breast milk.
Source: Adapted from WHO/UNICEF/ICCIDD (2007)
WHO considers a population iodine deficient if the median UIC is less than 100 μg/L (by definition, when the median is 100 μg/L, then 50% of the results will be lower than 100 μg/L). They also recommend that no more than 20% of the population have iodine concentrations below 50 μg/L (WHO/UNICEF/ICCIDD 2007; WHO 2013).
Interpretation
Points to be considered when interpreting data for this topic include the following:
- UIC from a single spot sample is not a sufficient measure to assess an individual's iodine status, thus comparing the iodine data items to other items at the individual level should be done with caution.
- UIC results do not confirm a specific diagnosis of deficiency without consultation with a health professional.
- There are several different test methods to measure iodine levels and each test method may produce different results. The data from this topic should therefore be used with caution when comparing iodine results from other studies using a different test method.
Comparison to other iodine biomarker data
This is the second time the ABS has collected information on iodine levels. Iodine was previously collected in the NHMS 2011–12 and the NATSIHMS 2012–13. For information on time series comparability, see Comparing biomedical collections over time.
Iodine data has been collected in other non-ABS surveys. However, caution must be taken when interpreting results due to the differences in scope, assay and the instrument used, and any thresholds applied in the final analysis.
References
Australian Institute of Health and Welfare (AIHW) (2011a), Mandatory folic acid and iodine fortification in Australia and New Zealand: baseline report for monitoring, AIHW, Australian Government, accessed 20/02/2025.
Australian Institute of Health and Welfare (AIHW) (2011b), Mandatory folic acid and iodine fortification in Australia and New Zealand: supplement to the baseline report for monitoring, AIHW, Australian Government, accessed 20/02/2025.
Australian Institute of Health and Welfare (AIHW) (2016), Monitoring the health impacts of mandatory folic acid and iodine fortification 2016, AIHW, Australian Government, accessed 20/02/2025.
Caldwell KL, Brook Maxwell C, Makhmudov A, Pino S, Braverman LE, Jones RL, Hollowell JG (2003), Use of Inductively Coupled Plasma Mass Spectrometry to Measure Urinary Iodine in NHANES 2000: Comparison with Previous Method, Clinical Chemistry, 49(6):1019-1021, accessed 20/02/2025.
Gibson RS (2005), Principles of Nutritional Assessment, 2nd edn, Oxford University Press.
Jooste PL, Strydom E (2010), Methods for determination of iodine in urine and salt, Best practice and Research Clinical Endocrinology and Metabolism; 24(1):77-88, accessed 20/02/2025.
Li M, Eastman CJ, Waite KV, Ma G, Zacharin MR, Topliss DJ, Harding PE, Walsh JP, Ward LC, Mortimer RH, Mackenzie EJ, Byth K and Doyle Z (2006), Are Australian children iodine deficient? Results of the Australian National Iodine Nutrition Study, Medical Journal of Australia, 184(4):165-169, accessed 20/02/2025.
Li M, Ma G, Guttikonda K, Boyages SC, Waite K and CJ Eastman (2001), Re-emergence of iodine deficiency in Australia, Asia Pacific Journal of Clinical Nutrition, 10(3):200-203, accessed 20/02/2025.
Li Y, Ding S, Han C, Liu A, Shan Z, Ten W, Mao J (2021), Concentration-dependent Differences in Urinary Iodine Measurements Between Inductively Coupled Plasma Mass Spectrometry and the Sandell-Kolthoff Method, Biological Trace Element Research, 199:2489–2495, accessed 20/02/2025.
National Health and Medical Research Council (NHMRC) (2013), ‘Iodine’ Nutrient Reference Values for Australia and New Zealand, Eat for Health website, accessed 07/02/2024.
Royal College of Pathologists of Australasia (RCPA) (2023), ‘Iodine Urine’, RCPA Manual, RCPA website, last accessed 07/02/2024.
Singh GR, Davison B, Ma GY, Eastman J, Mackerras DEM (2019), Iodine status of Indigenous and non‐Indigenous young adults in the Top End, before and after mandatory fortification, Medical Journal of Australia, 210(3):121-125, accessed 20/02/2025.
World Health Organization (WHO) (2013), Urinary iodine concentrations for determining iodine status in populations, WHO, accessed 20/02/2025.
World Health Organization (WHO) (27 April 2022), Maternal, infant and young child nutrition: sustaining the elimination of iodine deficiency disorders, 75th World Health Assembly, accessed 20/02/2025.
World Health Organization/United Nations Children’s Emergency Fund/International Council for Control of Iodine Deficiency Disorders (WHO/UNICEF/ICCIDD) (2007), Assessment of iodine deficiency disorders and monitoring their elimination: a guide for programme managers, 3rd ed, WHO, accessed 20/02/2025.