Iodine nutrition of pregnant and lactating women in Hong Kong, where intake is of borderline sufficiency

Abstract

Objective: To describe the iodine nutrition of pregnant and lactating women in Hong Kong, where intake is of borderline sufficiency. Design: Review of cross-sectional and prospective studies. Setting: China, Hong Kong Special Administrative Region (SAR). Subjects: Pregnant and lactating women. Results: Studies of pregnant women in Hong Kong SAR have revealed an increase in the urinary iodine (UI) concentration as pregnancy advances. A significant percentage of women had a sub-normal serum thyroid hormone concentration at full term. Although iodine is concentrated by the mammary gland, 19% of all mothers had low iodine concentrations in their breast milk. The moderate correlation between the concentrations of iodine in breast milk and urine suggests that an adequate maternal urinary iodine concentration cannot reliably indicate that an infant is getting enough iodine in breast milk. Therefore, some breast-fed infants may still be at risk of low iodine intake, and additional iodine supplements, other than salt iodisation, would be warranted in this population. Conclusions:The currently recommended intake of iodine through universal salt iodisation may not be adequate for pregnant and lactating women, and supplementation during pregnancy and lactation should be further considered in light of the latest recommendations. KeywordsIodine Deficiency Pregnancy Lactation Urinary iodine Hong KongAn adequate iodine intake during pregnancy and lactation is important because both the foetus and the neonate are particularly vulnerable to the harmful effects of deficiency. The clinical consequences of severe iodine deficiency (ID) are easily recognised, but the effects of mild to moderate deficiency are often overlooked: thyroid enlargement in both the mother and the neonate, and hypothyroidism, hyperthyrotropinaemia and impaired neuropsychological development of the neonate 1 . In localities in which the iodine intake of the general population is adequate because of complete or partial salt iodisation programmes, the problem of ID in pregnant and lactating women, and hence in neonates, is minimal. Even in countries with a recently introduced but well-monitored salt iodisation programme, such as China, the goitre rate is low at about 5%, and the median urinary iodine (UI) concentrations of women of reproductive age and those who are pregnant and lactating indicate an adequate iodine nutrition 2 . This suggests that salt iodisation can prevent ID not only in schoolchildren, but also in pregnant mothers and their neonates. A randomised controlled study in China confirmed that infants born to mothers supplemented with iodised salt had significantly better gross motor function, language skills and development quotient, and that the percentage of infants born with a sub-normal development quotient was significantly lower than in controls 3 . A study in an area with an effective salt iodisation programme among the general population found that infants born with a concentration of thyroid-stimulating hormone (TSH) in cord bloo...

Trimester- and method-specific reference intervals for thyroid tests in pregnant Chinese women: methodology, euthyroid definition and iodine status can influence the setting of reference intervals

“…, 26 our data showed relatively higher cut‐off values for FT4 reference interval, especially for the second trimester (10·6–17·6 pmol/l vs 8·1–16·7 pmol/l). Data from Kung and her group at that time revealed that mild iodine deficiency or borderline iodine sufficiency has previously existed in Hong Kong and resulted in goitrogenesis and hypothyroxinaemia in pregnant women, as well as neonatal hypothyroidism 33–35 . The different iodine status between these two groups of Chinese women is important when setting reference intervals.…”

Iodine Supplementation in Pregnancy and the Dilemma of Ambiguous Recommendations

“…Thus, no universal rule can be given on the association between UIC in schoolchildren and in pregnant women. Similarly, the reports on the change in UIC during the three trimesters of pregnancy are diverse [3], with some authors reporting an increase [22,23,24,25,26], other researchers a decrease [27,28,29,30] and still other authors observing no change [31,32,33,34,35] between the different trimesters of pregnancy. No consistent pattern in the median UIC by trimester of pregnancy can be derived from these studies.…”

Benefits of Docosahexaenoic Acid, Folic Acid, Vitamin D and Iodine on Foetal and Infant Brain Development and Function Following Maternal Supplementation during Pregnancy and Lactation

“…Numerous population studies from a variety of countries including China, Hong Kong, Iran, India, Kyrgyzstan and England have reported iodine deficiency in girls of child bearing age [76], in pregnant [154,155,156,157], and in pregnant and lactation women [158,159]. Some of these studies included regions where salt iodization is practiced, yet a significant proportion of pregnant and lactating women were still deficient [155,156,157,158,159,160,161].…”

“…Some of these studies included regions where salt iodization is practiced, yet a significant proportion of pregnant and lactating women were still deficient [155,156,157,158,159,160,161]. A few examples of recent studies follow:…”

“…The moderate correlation between the concentrations of iodine in breast milk and urine suggests that an adequate maternal urinary iodine concentration cannot reliably indicate that an infant is getting enough iodine in breast milk. Therefore, some breast-fed infants may still be at risk of low iodine intake, and additional iodine supplements, other than salt iodisation, would be warranted in this population [158]. …”