Iodine Status of Mother-Infant Dyads from Montréal, Canada: Secondary Analyses of a Vitamin D Supplementation Trial in Breastfed Infants

Minimizing neonatal hypothyroidism induced by lithium exposure through breast milk

BACKGROUND

Lithium-induced hypothyroidism in the neonate is a growing concern for lactating mothers. Maternal hypothyroidism in the postpartum period could lead to hypothyroidism in the infant via maternal compromised thyroid hormones (likely T4) in breast milk, and lithium in breast milk could have a direct effect on the neonatal thyroid axis over lithium carbonate direct administration.

METHODS

We have studied the effects of lithium exposure on neonatal pups through two different modes of exposure: direct oral administration of lithium carbonate and indirect exposure of lithium from breast milk from dams. Furthermore, dams were supplemented with two different iodine dosages in both control and lithium-treated groups. We employed Enzyme-linked immunosorbent assay, inductively coupled plasma mass and atomic absorption spectrometry to assess hormone profiles and intrathyroidal elemental content.

RESULTS

Interestingly, lithium administered directly to pups from control mothers (average dose 900 mg/50 kg per day), did not affect their weight, thyroid hormones, blood urea, and intrathyroidal iodine content despite traces of lithium found in their blood and thyroid. The iodine pathway in the presence of lithium content in both thyroid follicular cells and lactocyte has been hypothesized. The results also demonstrate that lithium administration in lactating dams alters thyroid hormones (T4) and blood urea in both dams and pups, which could be reversed by iodine supplement. The mechanism for supplemented iodine uptake in the presence of lithium is hypothesized.

CONCLUSION

In future, supplementing iodine may be potentially useful in clinical practices to address the neonate concerns of lactating mothers and their infants either caused by prolonged lithium medication or maternal iodine deficiency.

Iodine intakes of pregnant females from Québec, Canada

BACKGROUND

Adequate maternal iodine intake is important for fetal brain development. Based on iodine intakes of non-pregnant females of reproductive age from the Canadian Health Measures Survey (2016 -2017) it can be extrapolated that most pregnant females in Canada will not meet iodine requirements without supplementation.

OBJECTIVES

To assess iodine intakes of 500 pregnant, nulliparous females from Québec, Canada and report on use of multivitamin/mineral (MVM) supplements and coverage of iodized salt.

METHODS

Duplicate spot urine samples were collected at 10.1 -14.9 weeks (T1) and 19.7 -24.9 weeks (T2) of gestation. Median urinary iodine concentrations (UIC) were compared with WHO/UNICEF/ICCIDD reference ranges. Daily iodine intakes were calculated from UIC using a formula that corrects for urine dilution using creatinine and accounts for urinary iodine excretion rate. Usual (adjusted for within-person variation) iodine intakes were estimated from duplicate daily intake measurements (T1 and T2 measures) using the National Cancer Institute method. Prevalence of inadequate or excessive intakes were determined from usual intakes by the Estimated Average Requirement (EAR) or Tolerable Upper Intake Level (UL) cut-point method, respectively.

RESULTS

Females (median: 30.1 years) were mostly white race (94.4 %), highly educated and consumed iodized salt (92 %). Median UIC at T1 (136 µg/L, IQR: 71 -230) was lower (p<0.001) than at T2 (193 µg/L, IQR: 112 -390). Almost all females used a MVM supplement (98.2 %) with 35.6 % starting supplementation preconception and 0.6 %, 28.4 %, 19.8 %, 7.2 % and 6.0 % starting 1 -2 weeks, 3 -4 weeks, 5 -8 weeks, 8 -12 weeks and > 12 weeks postconception, respectively. Almost all (99 %, 95 % CI: 98, 100) had usual iodine intakes ≥EAR and ≤UL.

CONCLUSIONS

Prevalence of inadequate or excessive usual iodine intakes was low. However, about two-thirds of females started MVM supplementation postconception and median UIC at T1 was below the adequate range of 150 -249 µg/L.

Impact of iodine supply in infancy and childhood

PURPOSE OF REVIEW

To assess the most relevant articles on the impact of iodine supply in at-risk populations, namely infants and young children, pregnant and lactating women.

RECENT FINDINGS

The 2022 Iodine Global Network Annual Report confirmed the dramatic decrease of severe iodine deficiency over the last 30 years, thanks to universal iodine iodization. However, mild to moderate deficiency is still present in many countries, where recent data showed a decrease of iodine intake and an impairment of iodine status. Unfortunately, there is yet no validated biomarker to classify the iodine status at the individual level. Available data show that there is no clear evidence to link mild-to-moderate iodine deficiency to adverse health outcomes in pregnant and lactating women as well as in infants and children. The description of a negative impact of maternal iodine excess on neurodevelopment of infants is of concern.

SUMMARY

Optimization of salt iodization (e.g. careful increase in iodine concentration in salt, use by food industry in processed foods) combined with targeted, personalized supplementation under medical supervision if needed (e.g. low intake of iodine rich foods, vegan diet) seems currently preferable to blanket supplementation.

Human Milk Nutrient Composition Data is Critically Lacking in the United States and Canada: Results from a Systematic Scoping Review of 2017-2022

Characterization of the nutrients in human milk is important to understand the dietary and developmental requirements of infants. The objective of this review was to summarize the state-of-the-science on the nutrient composition of human milk in the United States and Canada published from 2017 to 2022. Four databases were searched for randomized controlled studies and others given the scoping nature of this review. We limited type to mature milk collected 21 d postpartum and beyond from lactating individuals in the United States and Canada who gave birth at 37-wk gestation or later (full-term). Outcomes of interest included traditional macro- and micronutrients, including human milk oligosaccharides (HMOs), and milk volume. The publication date range was selected as January 1, 2017, to the day the literature search was performed. A total of 32 articles were included in the scoping review from primarily longitudinal cohort or cross-sectional designs. The most prevalent sample collection method was full-breast expression (n = 20) with most studies (n = 26) collecting samples from a single timepoint. Carbohydrates (HMOs [n = 12], glucose [n = 8], and lactose [n = 6]) and protein (n = 5) were the most frequently assessed nutrients in this body of work, with consensus among studies that glucose is present in limited concentrations compared to lactose (24-64 mg/dL compared with 6-7 g/dL) and that HMOs are influenced by temporality and secretor status. Included studies displayed an overall level of heterogeneity and sparsity paralleling previous reports and nutrient data in the USDA FoodData Central system. Much of the data extracted from retained articles generally provided analysis of a specific nutrient or group of nutrients. Moreover, many studies did not use the preferred analytical methods as outlined by the Human Milk Composition Initiative to increase measurement confidence. Up-to-date nutrient composition data of human milk is still greatly needed as it is paramount for the management of infant feeding, assessment of infant and maternal nutritional and health needs, and as a reference for infant formula development.