Infant Iodine and Selenium Status in Relation to Maternal Status and Diet During Pregnancy and Lactation

Abstract

Iodine and selenium are essential trace elements. Recent studies indicate that pregnant and lactating women often have insufficient intake of iodine and selenium, but the impact on fetal and infant status is unclear. Here, we assessed iodine and selenium status of infants in relation to maternal intake and status of these trace elements in the birth cohort NICE, conducted in northern Sweden (n = 604). Iodine was measured in urine (UIC) in gestational week 29, and in breast milk and infant urine 4 months postpartum, while selenium was measured in maternal plasma and erythrocytes in gestational week 29, and in breast milk and infant erythrocytes 4 months postpartum, in both cases using ICP-MS. Maternal intake was assessed with semi-quantitative food frequency questionnaires in gestational week 34 and at 4 months postpartum. The median intake of iodine and selenium during pregnancy (98 and 40 μg/d, respectively) and lactation (108 and 39 μg/d, respectively) was below recommended intakes, reflected in insufficient status (median UIC of 113 μg/L, median plasma selenium of 65 μg/L). Also, breast milk concentrations (median iodine 77 μg/L, median selenium 9 μg/L) were unlikely to meet infant requirements. Median UIC of the infants was 114 μg/L and median erythrocyte selenium 96 μg/kg, both similar to the maternal concentrations. Infant UIC correlated strongly with breast milk levels (rho = 0.64, p < 0.001). Their erythrocyte selenium correlated with maternal erythrocyte selenium in pregnancy (rho = 0.38, p < 0.001), but not with breast milk selenium, suggesting formation of prenatal reserves. Our results indicate that the transport of iodine and selenium to the fetus and infant is prioritized. Still, it is uncertain whether most infants had sufficient intakes. Further, the results might indicate an involvement of iodine in asthma development during the first year of life, which is essential to follow up. The low maternal and infant dietary intake of both iodine and selenium, especially when the mothers did not use supplements or iodized table salt, suggest a need for a general screening of women and young children.

Assessment of Joint Impact of Iodine, Selenium, and Zinc Status on Women's Third-Trimester Plasma Thyroid Hormone Concentrations

“…The women included in this study had no known thyroid-related diagnosis and essentially all (98%) had TSH concentrations <4.0 mIU/L, indicative of normal thyroid function ( 26 ). They had generally low concentrations of iodine and selenium ( 22 ), which is in line with studies of pregnant women in other parts of Sweden ( 20 , 39–41 ). On the other hand, only 1% ( n = 6) had plasma zinc concentrations <500 μg/L [proposed lower limit of the late-pregnancy reference interval ( 18 )].…”

“…The wide CIs and credible intervals may be the result of UIC being an uncertain marker of iodine status on an individual level. Most of the absorbed iodine that is not taken up by the thyroid gland is rapidly excreted in urine ( 28 , 29 ), and most likely the women's iodine intake varied during the day, because iodized table salt and supplements containing iodine were the primary sources of iodine intake ( 22 ). Because the women were asked to fast before urine collection, the measured UIC, although likely rather stable, might in fact have underestimated the amount of iodine available to the thyroid, which is largely supplied by the peak plasma concentrations after a meal or supplementation.…”

“…Most nutrition-related studies of thyroid function have focused on iodine alone, including 2 recent studies from Sweden ( 20 , 21 ). In addition, we have recently reported that both iodine and selenium intakes in Swedish pregnant women are low ( 22 ). Therefore, we here aimed at elucidating the joint impact of iodine, selenium, and zinc status on thyroid hormone and TSH concentrations in pregnant women in northern Sweden.…”

Macrominerals and Trace Minerals in Commercial Infant Formulas Marketed in Brazil: Compliance With Established Minimum and Maximum Requirements, Label Statements, and Estimated Daily Intake

“…The need for essential trace minerals after childbirth is often greater than during the fetal period because of the high activity of metabolic pathways involved in growth, repair, and development, and in infection or hazardous physiopathological condition defense ( 3 , 4 ). Macrominerals and trace minerals account for about 4% of total human body mass and are extremely important during infant feeding, since each mineral performs essential and specific physiological functions ( 6 , 8 ), and appropriate intake of several macrominerals and trace minerals is crucial for child growth and development ( 9 , 10 ).…”

“…These elements participate in several important reactions in the human body. Both Ca and P, for example, are required for skeletal development and bone mineralization during the fetal development and postnatal periods ( 9 , 12 – 14 ), while Mg acts as a cofactor in enzymes responsible for several metabolic activities, accounting for innate and acquired immune responses, neuromuscular signaling and muscle contraction, protein and nucleic acid metabolism and bone growth and plays a role in maturation of lymphoid cells and tissues, as well as several enzyme activities ( 12 , 14 ). Mn is an essential nutrient for skeletal structure, amino acid metabolism, and cholesterol and carbohydrates synthesis, and acts as a cofactor in several enzymes ( 15 , 16 ).…”