Type of Papers: Reports completed by expert consultations and published by the World Health Organization jointly with the Food and Agriculture Organization of the United Nations (FAO).
Note: Two WHO reports were summarized together as they contain much of the same information. See references below.
- All of iodine’s physiological functions are through thyroid hormones. Thyroid function is involved in growth and development and the control of metabolic processes.
Prevalence of Deficiency:
- The World Health Organization estimates that 2 billion people worldwide have inadequate iodine nutrition. Iodine deficiency is a major public health problem throughout the world.
- Iodine deficiency varies by geographical region, with the highest prevalence in South-East Asia and Europe.
- In some regions, such as parts of Europe, iodine deficiency is returning even after being eliminated.
Risk Factors for Deficiency:
- The main risk factor is low dietary iodine intake due to living in an area with low levels of iodine in the soil.
- Consumption of goitrogens (foods that interfere with iodine metabolism) can also increase the risk for iodine deficiency (e.g., cassava).
- Thyroid stimulating hormone (TSH) levels and serum thyroxine (T4)
- On a population level, median urinary iodine concentrations are recommended to monitor the efficacy of interventions to improve iodine deficiency. Urinary iodine reflects current iodine intake and improves quickly with iodine interventions.
Dietary Sources and Bioavailability:
- The iodine content in food varies by geographical location. Iodine is found in the soil, and thus the iodine content in food depends on the iodine levels in the soil in which the food is grown or raised.
- The order of regions from those most affected by iodine deficiency to those least affected is: South-East Asia, Europe, the Western Pacific, Africa, the Eastern Mediterranean, and the Americas.
- Seawater is rich in iodine, and therefore seaweed and reef fish are good dietary sources of iodine.
- Goitrogens are present in some staple foods, such as cassava. Goitrogens interfere with thyroid iodine metabolism and can increase the risk for deficiency.
Recommended Nutrient Intakes: The following are the Recommended Nutrient Intakes (RNI) as defined by the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization.
- The general recommendation is 90 µg/day for infants and children (0-59 months of age).
- This is approximately equivalent to 15 µg/kg/day in term infants (0 – 12 months).
- Pre-term infants need twice the amount of iodine than term infants based on body weight. 30 µg/kg/day is recommended in pre-term infants.
- The recommended iodine content of formula (based on an intake of 150 ml/kg/day of formula) is:
- Term infants: 100µg/l
- Pre-term infants: 299µg/l
- Excess iodine can be harmful. The threshold for the upper limit depends on the iodine level prior to the exposure to the excess iodine and the age of the individual. Younger infants are more sensitive to excess iodine.
- In general, the benefits of correcting a deficiency outweigh the risks of iodine supplementation.
- The tolerable upper limit (UL) for iodine in children ages 1-3 years is 200 µg/day
- Universal salt iodization is the method recommended by the World Health Organization to correct iodine deficiency.
Health Consequences of Deficiency and Benefits of Intervention:
- Health Consequences of Deficiency:
- Effects of iodine deficiency include hypothyroidism and goiter, impaired mental function, and restricted physical development.
- Iodine deficiency during pregnancy and in children younger than 3 years of age has particularly profound effects, specifically cognitive and neurological impairment:
- Thyroid hormones are critical for growth and development of the brain and central nervous system during fetal development and during the first 3 years of life. Therefore, iodine deficiency during this time results in irreversible brain damage and impaired mental function.
- Severe iodine deficiency during early pregnancy leads to the syndrome of cretinism, characterized by irreversible mental retardation and stunted growth.
- Iodine deficiency is the world’s most common preventable cause of cognitive impairment.
- In regions with severe iodine deficiency, iodine deficiency is associated with more than a 13 point drop in IQ.
Iodine. Vitamin and mineral requirements in human nutrition. Report of a joint FAO/WHO expert consultation on human vitamin and mineral requirements, Bangkok, Thailand, 21–30 September 1998. 2nd ed. Geneva: World Health Organization, 2004:303-317.