Iodine Requirements in Infancy

Reference from the joint report of FAO/WHO expert consultation on Human Vitamins and Minerals verbatim.

Iodine requirements in infancy

Delange, F., Bourdoux, P., Chanoine, J.P. & Ermans, A.M. 1988. Physiopathology of iodine nutrition during pregnancy, lactation and early postnatal life. In: Vitamins and minerals in pregnancy and lactation. Berger, H., eds., New York, Raven Press, Nestle Nutrition Workshop Series, 16: 205-13.

Gushurst, C.A., Mueller, J.A., Green, J.A. & Sedor, F. 1984. Breast milk iodide: reassessment in the 1980s. Pediatrics, 73: 354-57.

The US recommendation of 40 μg/day for infants aged 0–6 months (or 8 μg/kg/day, 7 μg/100 kcal, or 50 μg/l milk) is probably derived from the observation that until the late 1960s the iodine content of human milk was approximately 50 μg/l and from the concept that nutrition of the human-milk-fed infant growing at a satisfactory rate has been the standard against which nutrition requirements have been set.

Delange, F., Bourdoux, P., Chanoine, J.P. & Ermans, A.M. 1988. Physiopathology of iodine nutrition during pregnancy, lactation and early postnatal life. In: Vitamins and minerals in pregnancy and lactation. Berger, H., eds., New York, Raven Press, Nestle Nutrition Workshop Series, 16: 205-13.

Bruhn, J.A., & Franke, A.A. 1983. Iodine in Human milk. J Daily Sci., 66: 1396-98.

However, more recent data indicate that the iodine content of human milk varies markedly as a function of the iodine intake of the population. For example, it ranges from 20 to 330 μg/l in Europe and from 30 to 490 μg/l in the United States. It is as low as 12 μg/l under conditions of severe iodine deficiency. An average human-milk intake of 750 ml/day would give an intake of iodine of about 60 μg/day in Europe and 120 μg/day in the United States. The upper US value (490 μg/l) would provide 368 μg/day or 68 μg/kg/day for a 5-kg infant. 

Delange, F. 1993. Requirements of iodine in Humans. In: Iodine deficiency in Europe. A continuing concern. Delange F., Dunn J.T., Glinoer D.eds, p. 5-16. New York, Plenum Press.

Positive iodine balance in the young infant, which is required for the increasing iodine stores of the thyroid, is achieved only when the iodine intake is at least 15 μg/kg/day in full-term infants and 30 μg/kg/day in pre-term infants. 

The iodine requirement of pre-term infants is twice that of term infants because of a 50 percent lower retention of iodine by pre-term infants. This corresponds approximately to an iodine intake of 90 μg/day. (This is probably based on the assumption of average body weight of 6 kg for a child of 6 months, the mid-age of an infant.) This value is twofold higher than the US recommendations.

World Health Organization. 1996. Trace elements in Human nutrition and health. p. 49-71. Geneva: World Health Organization Publication, Geneva. 

On the basis of these considerations, a revision is proposed for the earlier World Health Organization (WHO), United Nations Children’s Fund (UNICEF), and International Council for the Control of Iodine Deficiency Disorders (ICCIDD) recommendations: an iodine intake of 90 μg/day from birth onwards is suggested. To reach this objective, and based on an intake of milk of about 150 ml/kg/day, the iodine content of formula milk should be increased from 50 to 100 μg/l for full-term infants and to 200 μg/l for pre-term infants.

Delange, F., Heidemann, P., Bourdoux, P., Larsson, A., Vigneri, R., Klett, M., Beckers, C. & Stubbe, O. 1986. Regional variations of iodine nutrition and thyroid function during the neonatal period in Europe. Biol. Neonate, 49: 322-30.

Delange, F., Dalhem, A., Bourdoux, P., Lagasse, R., Glinoer, D., Fisher, D.A., Walfish, P.G. & Ermans, A.M. 1984. Increased risk of primary hypothyroidism in preterm infants. Pediatrics, 105: 462-69. 

For a urine volume of about 4–6 dl/day from 0 to 3 years, the urinary concentration of iodine indicating iodine repletion should be in the range of 150–220 μg/l (1.18-1.73μmol/l) in infants aged 0–36 months. Such values have been observed in iodine-replete infants in Europe, Canada, and the United States. Under conditions of moderate iodine deficiency, as seen in Belgium, the average urinary iodine concentration is only 50–100 μg/l (0.39-0.79μmol/l) in this age group. It reaches a stable normal value of 180–220 μg/l (1.41- 1.73μmol/l) only after several months of daily iodine supplementation with a physiologic dose of 90 μg/day (Figure 21).

Delange, F. 1989. Iodine nutrition and congenital hypothyroidism. In: Research in congenital hypothyroidism. Delange F., Fisher D.A., Glinoer D., eds. p. 173-85. New York, Plenum Press Publication.

Delange, F. 1986. Anomalies in physical and intellectual development associated with severe endemic goitre. In: Towards the eradication of endemic goitre, cretinism and iodine deficiency. Dunn J.P., Pretell E.A., Daza C.H., Viteri F.E. eds. p. 49-67. Pan American Health Organization, Washington, D.C., Sc. Publication no. 502. 

When the urinary iodine concentration in neonates and young infants is below a threshold of 50-60 μg/l (0.39-0.47μmol/l), corresponding to an intake of 25–35 μg/day, there is a sudden increase in the prevalence of neonatal serum TSH values in excess of 50 mU/ml, indicating sub-clinical hypothyroidism and eventually complicated by transient neonatal hypothyroidism. When the urinary iodine concentration is in the range of 10–20 μg/l (0.08-0.16μmol/l), as observed in severe endemic goitre regions, up to 10 percent of the neonates have overt severe hypothyroidism, with serum TSH levels above 100 mU/mL and serum T3 values below 30 μg/l (39 nmol/L). Untreated, these infants progress to myxedematous endemic cretinism.

Thus, the iodine requirement of the young infant approximates 15 μg/kg/day (30 μg/kg/day in pre-term infants). Hyperthyrotropinemia (high levels of serum TSH), indicating sub-clinical hypothyroidism with the risk of brain damage, occurs when the iodine intake is about one-third of this value, and dramatic neonatal hypothyroidism resulting in endemic cretinism occurs when the intake is about one-tenth of this value.