Iodine deficiency

What does this indicator tell us?

This indicator allows an assessment of iodine deficiency at the population level. Iodine is an essential trace element that is present in the thyroid hormones, thyroxine and triiodotyronine. It occurs most frequently in areas where there is little iodine in the diet – typically, these are remote inland areas where no marine foods are eaten. Urinary iodine concentration in children aged 6–12 years is included as an additional indicator in the WHO Global reference list of 100 core health indicators.

How is this indicator defined?

Although goitre assessment by palpation or ultrasound may be useful for assessing thyroid function, results are difficult to interpret once salt iodization programmes have started. The median urinary iodine concentration is considered to be the main indicator of iodine status for all age groups, because its measurement is relatively noninvasive, cost-efficient and easy to perform. Since most of the iodine absorbed by the body is excreted in the urine, it is considered to be a sensitive marker of current iodine intake and can reflect recent changes in iodine status. Median urinary iodine concentrations have been most commonly measured in school children aged 6–12 years, because it is easy to access this population.

For school-age children (≥6 years of age), an adequate iodine level is defined as a population median urinary iodine concentration of 100–199 μg/L, whereas a population median of <100 μg/L indicates that the population’s iodine intake is insufficient. When the population median is <20 μg/L, the population is described as having severe iodine deficiency; at 20–49 μg/L, it is described as having moderate iodine deficiency; and at 50–99 μg/L, it is described as having mild iodine deficiency. A population of school-age children should have a median urinary iodine concentration of at least 100 μg/L, with less than 20% of values being <50 μg/L. For pregnant women, the median urinary iodine should be between 150 µg/L and 249 μg/L.

What are the consequences and implications?

Iodine-deficiency disorders, which can start before birth, jeopardize children’s mental health and often their very survival. During the neonatal period, childhood and adolescence, iodine-deficiency disorders can lead to hypothyroidism and hyperthyroidism. Serious iodine deficiency during pregnancy can result in stillbirth, spontaneous abortion and congenital abnormalities such as cretinism – a grave, irreversible form of mental retardation that affects people living in iodine-deficient areas of Africa and Asia. Of even greater significance is the less visible, yet pervasive, mental impairment that reduces intellectual capacity at home, in school and at work.

Cut-off values for public health significance in different target groups

^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 concentration is lower because iodine is excreted in breast milk.

Source: WHO (2013).

Source of data

WHO. Vitamin and Mineral Nutrition Information System (VMNIS). Micronutrients database (http://www.who.int/vmnis/database/en/).

Further reading

WHO. Goitre as a determinant of the prevalence and severity of iodine-deficiency disorders in populations. WHO/NMH/NHD/MNM/14.5. Geneva: World Health Organization; 2014 (http://apps.who.int/iris/bitstream/10665/133706/1/WHO_NMH_NHD_EPG_14.5_eng.pdf).

WHO. Urinary iodine concentrations for determining iodine status deficiency in populations. Vitamin and Mineral Nutrition Information System. Geneva: World Health Organization; 2013 (http://www.who.int/nutrition/vmnis/indicators/urinaryiodine).

Andersson M, Karumbunathan V, Zimmermann MB. Global iodine status in 2011 and trends over the past decade. J Nutr. 2012;142:744–750.

WHO. Global reference list of 100 core health indicators (plus health-related SDGs). Geneva: World Health Organization; 2018 (https://www.who.int/healthinfo/indicators/2018/en/).

Internet resources

WHO. Vitamin and Mineral Nutrition Information System (VMNIS). Urinary iodine concentrations for determining iodine status deficiency in populations (http://www.who.int/vmnis/indicators/urinaryiodine/en/).

WHO. Iodine deficiency list of publications. (http://www.who.int/nutrition/publications/micronutrients/iodine_deficiency/en/).