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

Abstract

Background Most pregnant or lactating women in Canada will not meet iodine requirements without iodine supplementation. Objective To assess iodine status of 132 mother-infant pairs based on secondary analyses of a vitamin D supplementation trial in breastfed infants from Montréal, Canada. Methods Maternal iodine status was assessed using breastmilk iodine concentration (BMIC). Singleton, term-born infants were studied from 1−36 mo of age. Usual (adjusted for within-person variation) iodine intakes were estimated from urinary iodine and creatinine concentrations. Iodine status was assessed using median urinary iodine concentrations (UIC) and by estimating inadequate intakes by the cut-point method using a proposed Estimated Average Requirement for infants 0−6 mo of age (72 µg/d). Results At 1, 3 and 6 mo of age, 70%, 63% and 3% of infants were exclusively breastfed, respectively. From 1−36 mo of age (n = 82−129), median UIC were ≥100 µg/L (range: 246−403 µg/L), the cutoff for adequate intakes set by the WHO for children <2 y. Almost all (98−99%) infants 1 and 2 mo, 2 and 3 mo and 3 and 6 mo of age had usual creatinine-adjusted iodine intakes ≥72 µg/d. Median BMIC was higher (p<0.001) at 1 mo compared to 6 mo of lactation: 1 mo, 198 µg/kg (IQR: 124, 274; n = 105) and 6 mo, 109 µg/kg (IQR: 67, 168; n = 78). At 1 mo 96% and at 6 mo 79% of mothers had a BMIC ≥60 µg/kg, the lower limit of a normal reference range. Percentage of mothers that used a multivitamin-mineral (MVM) supplement containing iodine was 90% in pregnancy and 79% at 1 mo and 59% at 6 mo of lactation. Conclusions Iodine status of infants was adequate throughout infancy. These results support a recommendation that all women, who could become pregnant, or women who are pregnant or breastfeeding take a daily MVM supplement containing iodine. clinicalTrials.gov identifier: NCT00381914.

Impact of iodine supply in infancy and childhood

“…The percentage of mothers using an iodine-containing supplement was 90% during pregnancy and 79% and 59% at 1 and 6 months of lactation, respectively. Bertinato et al [21 ▪ ] concluded that the iodine status of these mostly breastfed infants was adequate throughout infancy and these results support the recommendation that all pregnant and lactating women take a daily iodine supplement. A study from China assessed the iodine status of 556 390 schoolchildren enrolled in the 2018 National IDD Surveillance.…”