Iodization of salt for the prevention and control of iodine deficiency disorders
All food-grade salt, used in household and food processing should be fortified with iodine as a safe and effective strategy for the prevention and control of iodine deficiency disorders in populations living in stable and emergency settings.
This guideline supersedes previous WHO recommendations on salt iodization (1, 2, 3).
Suggested concentrations for the fortification of food-grade salt with iodine.
Estimated salt consumptiona, g/day
Average amount of iodine to add, mg/kg salt (RNI + lossesb)
a. This includes consumption as table salt as well as salt from processed foods.
b. This fortification concentration was calculated based on the mean recommended nutrient intake of 150 μg iodine/day + 30% losses from production to household level before consumption, and a 92% iodine bioavailability. Losses depend on the iodization process, the quality of salt and packaging materials and the climatic conditions. Losses could vary widely (4) and this table presents the value considering 30% losses. The monitoring of urinary iodine concentrations will allow adjustment of the selected fortification concentrations.
c. An intake of < 5g of salt per day corresponds to WHO recommendations on sodium intake (5).
RNI: recommended nutrient intake, is the daily intake, set at the estimated average requirement plus 2 standard deviations, which meets the nutrient requirements of almost all apparently healthy individuals in an age- and sex-specific population group.
Although iodate is more stable, either potassium iodate (KIO3) or iodide (KI) can be used. Iodide may be used for dry, low crystal size and washed or refined salts. While iodate can be used alone and in any type of salt quality, iodide is used in very good quality salt and cannot be added alone. Therefore, some salt producers add sodium carbonate or sodium bicarbonate when they iodize salt, to increase alkalinity, and sodium thiosulfate or dextrose to stabilize potassium iodide. Without a stabilizer, potassium iodide may be oxidized to iodine and lost by volatilization from the product (6).
An estimated additional variability of ±10% during iodization procedures could be considered at the production site for use in quality control and assurance procedures. This variability depends on the iodization methods used and quality assurance system in place.
- These recommendations recognize that salt reduction and salt iodization are compatible. Monitoring of sodium (salt) intake and iodine intake at country level is needed to adjust salt iodization over time as necessary, depending on observed salt intake in the population, to ensure that individuals consume sufficient iodine despite reduction of salt intake (5).
- The concentrations of iodine may need to be adjusted by national authorities responsible for the implementation and monitoring of universal salt iodization, in light of their own data regarding dietary salt intake (7).
- The national distribution of salt consumption must provide key guidance for the concentration of iodine in salt (8, 9); sufficient iodine should be supplied to most members of the population, even those with the lowest salt intake, while at the same time preventing excessive iodine supply to those individuals whose salt intake remains high.
- Iodized salt should reach, and be used by, all members of the population after 1 year of age. Infants and young children are assumed to be covered via breast milk (10) or iodine-enriched infant formula milk when this is prescribed (11). Addition of salt to products consumed by young children may need regulation, to avoid insufficient or excessive consumption of either sodium (salt) or iodine.
- Since pregnant women have a daily iodine requirement of 250 µg/day, other interventions such as iodine supplementation could be considered if iodine inadequacy is found (12, 13). Intake of salt correlates with caloric intake, and pregnant women usually increase their energy intake during this physiological stage.
- Policies for salt iodization and reduction of salt to <5 g/day are compatible, cost effective and of great public health benefit. Although salt is an appropriate vehicle for iodine fortification, iodization of salt should not justify promotion of salt intake to the public (7).
- Monitoring of food-grade salt quality is essential to ensure both efficacy and safety of the process of iodine fortification. Monitoring of urinary iodine excretion (UIE) and urinary iodine concentration (UIC) is useful not only to detect deficiency but also to detect excessive intakes and therefore prevent the health risks of iodine excess, by adjusting the level of iodine fortification accordingly, as part of a monitoring system. Countries should determine iodine losses from iodized salt under local conditions of production, climate, packaging and storage. For these reasons, iodine losses may be extremely variable and influence the additional amount of iodine that should be added at factory level.
- Fortification of salt with iodine should be appropriately regulated by governments and harmonized with other local or country programmes, to ensure that fortified food-grade salt is delivered safely within the acceptable dosage range. Particular attention should be given to identifying potential barriers to equitable access for all population groups needing iodine-fortified salt.
- Country programmes should be culturally appropriate to the target populations, so the intervention is accepted, adopted and sustained.
- Clear legislation should also be established for food producers and distributors, especially where the main source of dietary salt is processed foods and meals consumed outside households. Legislation should cover not only proper iodization of salt, but also the salt content of industrialized food products.
- Establishment of an efficient system for the ongoing and routine collection of relevant data, including measures of quality assurance and household use of iodized salt, and measures of programme performance, is critical to ensure programmes for iodized salt are effective and sustained.
- Regular monitoring and evaluation can identify barriers that may be limiting equal access to fortified salt and thus preserving health inequities. Sustained implementation and scale-up derive great benefit from appropriate monitoring mechanisms (10).
* This is an extract from the relevant guideline (14). Additional guidance information can be found in this document.
1. WHO, UNICEF, ICCIDD. Assessment of iodine deficiency disorders and monitoring their elimination: a guide for programme managers, 3rd edition. Geneva, World Health Organization; 2007 (http://whqlibdoc.who.int/publications/2007/9789241595827_eng.pdf).
2. WHO, UNICEF, ICCIDD. Recommended iodine levels in salt and guidelines for monitoring their adequacy and effectiveness. Geneva:, World Health Organization; 1996 (http://whqlibdoc.who.int/hq/1996/WHO_NUT_96.13.pdf).
3. WHO. Iodine and health. Eliminating iodine deficiency disorders safely through salt iodization: a statement by the World Health Organization. Geneva, World Health Organization; 1994 (http://whqlibdoc.who.int/hq/1994/WHO_NUT_94.4.pdf).
4. Aburto NJ, Abudou M, Candeias V, Wu T. Effects and safety of salt iodisation to prevent iodine deficiency disorders: a systematic review with meta-analyses. 2014; (in press).
5. WHO. Guideline: Sodium intake for adults and children. Geneva, World Health Organization; 2012 (http://www.who.int/nutrition/publications/guidelines/sodium_intake_printversion.pdf).
6. The Salt Institute. Iodized salt (http://www.saltinstitute.org/news-articles/iodized-salt/).
7. WHO, ICCIDD Global Network. Salt reduction and iodine fortification strategies in public health. Report of a joint technical meeting convened by World Health Organization (WHO) and The George Institute for Global Health in collaboration with the International Council for the Control of Iodine Deficiency Disorders Global Network, Sydney, Australia, March 2013. Geneva, World Health Organization; 2013 (http://www.who.int/nutrition/events/2013_technicalconsultation_salt_iodine_strategies_25to27Mar2013/en/).
8. WHO. Salt as a vehicle for fortification. Report of a WHO expert consultation on salt as a vehicle for fortification. Luxembourg 21–22 March 2007. Geneva, World Health Organization; 2008 (http://www.who.int/nutrition/publications/micronutrients/978924159678/en/).
9. WHO. Strategies to monitor and evaluate population sodium consumption and sources of sodium in the diet: report of a joint technical meeting convened by WHO and the Government of Canada, November 2010. Geneva, World Health Organization; 2011 (http://whqlibdoc.who.int/publications/2011/9789241501699_eng.pdf).
10. Rohner F, Zimmermann M, Jooste P, Pandav C, Caldwell K, Raghavan et al. Biomarkers of nutrition for development-iodine review. Journal of Nutrition. 2014; 144(8):1322S–42S.
11. WHO, UNICEF. Acceptable medical reasons for use of breast-milk substitutes. Geneva, World Health Organization; 2009. (http://whqlibdoc.who.int/hq/2009/WHO_FCH_CAH_09.01_eng.pdf).
12. WHO, UNICEF. . Reaching optimal iodine nutrition in pregnant and lactating women and young children. Joint statement by the World Health Organization and the United Nations Children’s Fund. Geneva, World Health Organization; 2007 (http://www.who.int/nutrition/publications/WHOStatement__IDD_pregnancy.pdf).
13. Angermayr L, Clar C. Iodine supplementation for preventing iodine deficiency disorders in children. Cochrane Database of Systematic Reviews. 2009; (2):CD003819.
14. WHO. Guideline: Fortification of food-grade salt with iodine for the prevention and control of iodine deficiency disorders. Geneva, World Health Organization; 2014 (http://www.who.int/nutrition/publications/guidelines/fortification_foodgrade_saltwithiodine/en/).