Iodine status of postpartum women and their infants aged 3, 6 and 12 months: Mother and Infant Nutrition Investigation (MINI)

Abstract

To alleviate the re-emergence of iodine deficiency in New Zealand, two strategies, the mandatory fortification of bread with iodised salt (2009) and a government-subsidised iodine supplement for breastfeeding women (2010) were introduced. Few studies have investigated mother and infant iodine status during the first postpartum year, this study aimed to describe iodine status of mothers and infants at three, six, twelve months postpartum (3MPP,6MPP,12MPP). Partitioning of iodine excretion between urine and breastmilk of exclusive breastfeeding women at 3MPP was determined. In total 87 mother-infant pairs participated in the study. Maternal and infant spot urinary iodine concentration (UIC) and breastmilk iodine concentration (BMIC) were determined. The percentage of women who took iodine-containing supplements decreased from 46% at 3MPP to 6% at 12MPP. Maternal median UIC (MUIC) at 3MPP [82(46,157)µg/L], 6MPP [85(43,134)µg/L] and 12MPP [95(51,169)µg/L] < 100µg/L. The use of iodine-containing supplements increased MUIC and BMIC only at 3MPP. Median BMIC at all time points were below 75µg/L. Infant MUIC at 3MPP [115(69,182)µg/L] and 6MPP [120(60,196)µg/L] were below 125µg/L. Among exclusive breastfeeding women at 3MPP, an increased partitioning of iodine into breastmilk (highest proportion 60%) was shown at lower iodine intakes, along with a reduced fractional iodine excretion in urine (lowest proportion 40%), indicating a protective mechanism for breastfed infants’ iodine status. In conclusion, this cohort of postpartum women was iodine deficient. Iodine status of their breastfed infants were suboptimal. Lactating women who do not consume iodine rich foods and those who become pregnant again should take iodine-containing supplements.

The Role of Iodine for Thyroid Function in Lactating Women and Infants

“…It should be noted that disinfectants used during cesarian delivery may contain iodine and unintentionally exaggerate the BMIC in colostrum ( 281 ). A modest decline in BMIC over the course of lactation has been reported in longitudinal studies at low ( 276 , 282 ), adequate ( 255 , 256 ), and high iodine intakes ( 19 , 280 ), although not all studies agree ( 283 ). Cross-sectional studies indicate a similar trend ( 19 , 247 , 254 ) but results are mixed ( 203 , 258 ).…”

“…Maternal fluid intake influences the iodine concentration in urine, but has less impact on BMIC ( 249 ). The fractional iodine excretion in breast milk and urine may vary depending on the iodine intake and iodine status ( 250 , 276 ). We conducted an observational study in iodine-sufficient populations and found that proportionally more iodine is excreted in breast milk (two-thirds) than in urine (one-third) at low iodine intake compared to higher intake ( 250 ).…”

Characteristics and predictors of breast milk iodine in exclusively breastfed infants: Results from a repeated-measures study of iodine metabolism

“…A trend toward a moderate decrease in BMIC over the course of lactation has been found in longitudinal studies in iodine-deficient areas (22,23), iodine-sufficient areas (8, 24), and iodine-excessive areas (25). We also observed a gradual decrease in median BMIC with increasing infant age and body mass from 5 to 26 weeks postpartum.…”

Improving Iodine Status in Lactating Women: What Works?

“…The researchers found that in iodine-sufficient countries, as iodine intake decreased, iodine was increasingly partitioned into breast milk, and hence, the fraction of iodine in urine decreased, whereas in the iodine-deficient country, the proportion in of iodine in breast milk remained constant. A small New Zealand study ( n = 87) found a similar variance in partitioning of iodine between breast milk and urine dependent upon status [ 19 ]. Further, a recent Iranian study found that although maternal UIC and BMIC were associated with neonatal UIC, BMIC was the stronger predictor of neonatal UIC [ 20 ].…”

“…Using daily iodine supplementation to address deficiency has limitations as there are several barriers to supplement use and uptake is often less than optimal [ 62 ]. In small New Zealand studies of educated women, iodine supplement use ranged from 6 to 40% among breastfeeding women and reduced with infant age [ 19 ]; deficiency was evident among non-users of supplements. Iodine supplement use is also lower among mothers who are younger and less educated and among some ethnic groups (Māori or Pacifica in New Zealand and Indigenous Australians) [ 63 , 64 ].…”