(HealthDay News) – Excess maternal iodine supplementation can result in congenital hypothyroidism, according to a study published online July 26 in The Journal of Pediatrics.

Kara J. Connelly, MD, from the Oregon Health & Science University Doernbecher Children’s Hospital in Portland, and colleagues report on three cases of infants with congenital hypothyroidism detected through a newborn screening program.

The researchers found that levels of whole blood iodine extracted from their newborn screening specimens were about 10 times above mean control levels. All three infants also demonstrated elevated iodine content in their urine. Maternal history revealed that all three infants had been exposed to high levels of iodine and that the mothers were ingesting a supplement whose iodine content exceeded the recommended daily intake. This was confirmed by elevated iodine levels in maternal urine and breast milk.

“The three cases presented demonstrate the potential hazard in the increasing practice of the use of certain nutritional supplements containing iodine amounts far in excess of the 1,100µg/day total intake considered by the US Institute of Medicine to be the safe upper limit for ingestion,” the authors write.

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