Better iodine supplementation through breastfeeding

By MD Will Boggs

NEW YORK (Reuters Health) - Infants in regions of iodine deficiency respond better to indirect iodine supplementation via breastfeeding than to direct iodine supplementation, according to research done in Morocco.

The result wasn't what the researchers had expected.

"We hypothesized that direct supplementation would be more effective in improving iodine status in infants than indirect (maternal) supplementation," Dr. Maria Andersson from the Laboratory of Human Nutrition, ETH Zurich, in Switzerland told Reuters Health by email. "We were positively surprised to find that one large dose of iodized oil given lactating mothers provides adequate iodine to the infant."

"This route is superior for infant nutrition as mothers appear to store the supplemental iodine and provide the infant with small amounts of daily iodine via breast milk," Dr. Andersson said. "Giving supplemental iodine to lactating mothers is beneficial to both the infants and the mothers."

Although there are published guidelines on iodine supplementation, there are few data on iodized oil supplementation during lactation and infancy.

Dr. Andersson and colleagues assessed the efficacy and safety of the existing WHO-UNICEF-ICCIDD (International Council for the Control of Iodine Deficiency Disorders) recommendations for iodized oil supplementation in lactation and infancy. They compared single-dose direct supplementation of the infant (100 mg orally) with single-dose indirect supplementation through breast milk (400 mg orally to the mother) in a placebo-controlled study of 241 mother-infant pairs from the Atlas Mountains of southern Morocco, an area of historic endemic goiter.

Prior to supplementation, 82.5% of mothers and 62.5% of infants were iodine deficient, as determined by urinary iodine concentrations less than 100 mcg/L, the researchers reported in The Lanet Diabetes & Endocrinology, online November 22.

Iodized oil supplementation of the mothers improved their median urinary iodine concentration, although levels remained below the 100 mcg/L cutoff for iodine deficiency. Breast milk iodine concentrations were significantly higher in women who received iodine supplementation than in women who did not at all time points (three, six and nine months) beyond baseline.

Median urinary iodine concentrations improved among infants in both groups, but the increase was significantly greater among infants getting indirect supplementation than among those given direct supplementation. A substudy of eight infants suggested that the 100 mg iodine dose was poorly absorbed.

Infants receiving indirect supplementation were sufficient at three and six months and borderline deficient at nine months, whereas those on direct supplementation were sufficient only at six months and were borderline deficient at three and nine months.

The prevalence of hypothyroxinemia and hypothyroidism declined rapidly in both groups of infants, but the cumulative frequency of hypothyroxinemia remained higher at nine months in the direct-supplementation group (10.5%) than in the indirect supplementation group (3.7%).

Maternal iodine supplementation had no significant impact on TSH, T4, or the prevalence of thyroid disorders over the course of the study.

Although rates of severe delay in psychomotor development did not differ significantly between the indirect- and direct-supplementation groups (17.2% vs 25.0%, respectively), proportions in both groups were significantly higher than the expected frequency of 2.5% in the standard population.

"Breast milk is the best source of iodine for young infants and iodine supplementation can improve the iodine concentration of breast milk," Dr. Andersson concluded. "In regions of moderate-to-severe iodine deficiency without effective salt iodization programs, supplementing lactating women with a single dose of 400 mg iodine as oral iodized oil (given soon after delivery) can provide adequate iodine to their infants through breast milk for at least 6 months, enabling the infants to achieve euthyroidism."

Dr. Elizabeth Pearce from Boston University, who was not involved in the new work, said it was "not entirely surprising" that supplementing mothers would provide sufficient iodine for their infants as iodine is actively concentrated in breast milk.

"Infants, especially those with reflux, might have failed to completely ingest the direct iodine supplements, or possibly the 100 mg infant iodine dose simply was not sufficient," she added in an email to Reuters Health.

"Women in developed countries do not need high-dose (400 mg) annual iodine supplementation, as provided to the moderately-to-severely iodine deficient Moroccan women in this study," Dr. Pearce said. "However, mild iodine deficiency is present in many developed countries, including the UK, Australia, and among pregnant women in the US. The American Thyroid Association and Endocrine Society currently recommend 150 mcg daily iodine supplements for US women who are lactating. This study suggests that iodine supplementation for nursing women is beneficial for their infants' iodine status."

Dr. Sara C. Bath from the University of Surrey in the UK, who wrote a commentary on the report, told Reuters Health, "This research emphasizes that physicians should ensure that lactating women have sufficient iodine to supply iodine to the developing infant and in countries where breastfeeding rates are low, physicians should ensure that the infant is provided with an appropriate amount of iodine in the formula milk."

"In many developed countries, such as in the US, Australia, and New Zealand, a daily iodine supplement (as potassium iodide) is recommended rather than a bolus dose of iodine (as iodized oil)," she said in an email. "However, as the trial did not include a group that received a daily iodine supplement, further research in different settings is required to examine the effects of daily iodine supplementation on iodine status and thyroid function of the mother and infant, and also the effects on the cognitive development of the infant."

SOURCE: http://bit.ly/1cqt9em and http://bit.ly/1kjFT7b

Lancet Diabetes Endocrinol 2013.

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