Iodine requirements during pregnancy, lactation and the neonatal period and indicators of optimal iodine nutrition

Abstract

Objective: This paper re-evaluates the requirements for iodine during pregnancy, lactation and the neonatal period, and formulates original proposals for the median concentrations of urinary iodine (UI) that indicate optimal iodine nutrition during these three critical periods of life. This paper also discusses the measurements that are used to explore thyroid functions during the same periods. Design: An extensive and critical review of the literature on thyroid physiopathology during the perinatal period. Setting: Human studies conducted in various regions throughout the world. Subjects: Pregnant women, lactating women, and newborns. Results: The following proposals are made after extensive review of the literature: the requirement for iodine by the mother during pregnancy is 250-300 mg day -1 ; during lactation the requirement is 225-350 mg day -1 ; and during the neonatal period the requirement of the infant is 90 mg day -1 . The median UI that indicates an optimal iodine nutrition during these three periods should be in the range of 150-230 mg day -1 . These figures are higher than recommended to date by the international agencies. Conclusions: Pregnant women and young infants, but especially the second group, are more sensitive to the effects of an iodine deficiency (ID) than the general population because their serum thyroid-stimulating hormone (TSH) and thyroxine are increased and decreased, respectively, for degrees of ID that do not seem to affect thyroid function in the general population. Systematic neonatal thyroid screening using primary TSH could be the most sensitive indicator to monitor the process of ID control.

Iodine Status of Pregnant Women and Their Progeny in the Minho Region of Portugal

“…This is particularly relevant to the complications of ID because breast milk is usually the only source of iodine for newborns. Breast milk iodine is considered sufficient when values are in the range of 150-180 mg=L (4,11,14,17,18,(27)(28)(29)(30)(31)(32)(33)(34)(35). The median iodine content in breast milk was lower than this in our study.…”

“…Breast milk iodine was also below the recommended values of 150-180 mg=L (4,14), with a median of 95 mg=L at 3 days and of 70 mg=L at 3 months after delivery. Iodine in breast milk correlated with UI at 3 days (R ¼ 0.440, p < 0.01) and 3 months (R ¼ 0.456, p < 0.01) after delivery.…”

“…Other potential indices of ID, such as neonatal TSH, are not completely reliable due to many factors, including the timing of sample collection (1)(2)(3)(4)32,35,36). Although the present study showed that the newborns met the WHO criteria for desirable serum TSH concentrations (considered iodine sufficient if less than 3% of the newborns have TSH >5 mU=L), it is now well recognized that the regulation of TSH secretion in the newborn does not follow the same feedback mechanisms observed when the thyroid-pituitary axis is fully developed (6).…”

“…Particularly important is the role of thyroid hormones in normal brain development and cognition. It has been shown that insufficient iodine intake during pregnancy and lactation and in newborns may lead to irreversible brain damage (1)(2)(3)(4)(5)(6)(7)(8)(9). The severity of this impairment varies from cretinism, in regions of severe iodine deficiency (ID), to the inability of children to achieve their potential intelligence quotient, when iodine intake is mildly to moderately insufficient.…”

“…ID is, worldwide and after starvation, the most important preventable cause of mental retardation. Since 1990 it has been accepted as a basic human right that every child has the right to an adequate supply of iodine to ensure its normal development and that every mother has the right to an adequate iodine nutrition to ensure that her unborn child reaches its potential mental development (4). Further, it is believed that iodine-related neurodevelopmental deficits of future generations can be prevented by promoting universal salt iodination and the use of iodine supplements from the onset of pregnancy or when pregnancy is planned (1)(2)(3)(4)(5)(6)(7)(8)(9).…”