Moderate-to-Severe Iodine Deficiency in the “First 1000 Days” Causes More Thyroid Hypofunction in Infants Than in Pregnant or Lactating Women

Abstract

Iodine deficiency early in the life cycle-the "first 1000 days"-can cause hypothyroidism and irreversibly impair neuromotor development. However, the relative vulnerability among women and infants during this critical period is unclear, making it difficult for country-based programs with limited resources to prioritize their iodine interventions. Our aim was to determine the prevalence of thyroid hypofunction in women and infants living in an area of moderate-to-severe iodine deficiency. In a cross-sectional survey in Morocco, we measured urinary iodine concentrations (UICs) and concentrations of thyroid-stimulating hormone (TSH) and total or free thyroxine (TT4 or fT4, respectively) in women of reproductive age ( = 156), pregnant women ( = 245), and lactating women ( = 239) and their young infants ( = 239). We calculated daily iodine intakes and measured iodine concentrations in breast milk and household salt. We compared the incidence of hypothyroidism between the 3 groups of women and with the infants. Women of reproductive age, pregnant women, and lactating women had median (IQR) UICs of 41 (29-63), 32 (17-58), and 35 (19-62) μg/L; and estimated iodine intakes were ∼60%, 22%, and 26% of Recommended Nutrient Intakes (RNIs). The infants' median UIC was 73 (28-157) μg/L, which was greater than for all 3 groups of women ( < 0.001), and their dietary intakes were 27% of the RNI. The prevalence of hypothyroidism was not significantly different between the 4 groups, whereas the prevalence of hypothyroxinemia was higher in infants (40%) than in the 3 groups of women (11-14%) ( < 0.001). The median breast-milk iodine concentration was 42 (26-81) μg/L. Only 6% of salt samples were adequately iodized to a concentration of ≥15 ppm; 54% were inadequately iodized and 40% contained no measurable iodine. In an area of moderate-to-severe iodine deficiency, the prevalence of thyroid hypofunction is ∼4-fold higher in young infants compared with the 3 groups of women, suggesting that, in the "first 1000 days," infants are more vulnerable than their mothers and that programs should prioritize iodine prophylaxis for this group.

Supplementation during pregnancy with small‐quantity lipid‐based nutrient supplements or multiple micronutrients, compared with iron and folic acid, increases women's urinary iodine concentration in semiurban Ghana: A randomized controlled trial

“…In fact, there are similar reports from other countries showing low iodine status of pregnant women even when a national salt iodization programme is in place (Mao et al, ; Oral et al, ). We did not measure the iodine status of infants born to women in our study, but in Morocco (Stinca et al, ) the iodine status (as measured by total thyroxine) of infants whose mothers were iodine deficient appeared to be worse than that of the women themselves. Although the full impact of mild iodine deficiency during pregnancy on fetal development may not be known, the consequences could include increased risk of lower verbal intelligence quotient later in life (Bath, Steer, Golding, Emmett, & Rayman, ; Stinca et al, ).…”

“…We did not measure the iodine status of infants born to women in our study, but in Morocco (Stinca et al, 2017) the iodine status (as measured by total thyroxine) of infants whose mothers were iodine deficient appeared to be worse than that of the women themselves. Although the full impact of mild iodine deficiency during pregnancy on fetal development may not be known, the consequences could include increased risk of lower verbal intelligence quotient later in life (Bath, Steer, Golding, Emmett, & Rayman, 2013;Stinca et al, 2017). Maternal serum thyroid hormone concentration or production may, however, be normal even when mean UIC is as low as 33 μg/L (Cao et al, 1994;Caron et al, 1997;Pedersen et al, 1993;Silva & Silva, 1981), although it is not certain what else may be affected when UIC falls below the 150 μg/L WHO cut-off.…”

Excess iodine intake: sources, assessment, and effects on thyroid function

“…Iodine is a critical micronutrient during the first 1000 days of life . Iodine in breast milk is highly variable depending upon maternal iodine intake .…”

“…Iodine is a critical micronutrient during the first 1000 days of life. 3,4,15,[44][45][46] Iodine in breast milk is highly variable depending upon maternal iodine intake. 47,48 In iodine-sufficient populations, if iodine intake is borderline, iodine is preferentially partitioned into breast milk to safeguard infant requirements.…”

Moderate iodine deficiency among pregnant women in Hong Kong: revisit the problem after two decades

“…Recent study also highlighted the impact of iodine deficiency in the first 1000 days of life especially among breast-fed infants. 32 As the Hong Kong SAR Government is actively promoting breastfeeding, it is also important to ensure adequate iodine in lactating mothers and breast-fed infants. It is time to systematically revisit the iodine status of our local women at pre-conception, and during pregnancy and lactation.…”