TUESDAY, Aug. 21 (HealthDay News) -- Babies born with congenital hypothyroidism -- a condition that causes low or no thyroid hormone production -- shouldn't be given soy formula, new research indicates.
Soy can interfere with the absorption of levothyroxine, the medication that replaces the missing thyroid hormone. If babies and toddlers don't get enough replacement thyroid medication, their brains can't develop properly, experts note.
Two case studies that highlight the importance of this issue are detailed by doctors from the University of California, San Diego, in the September issue of the journal Pediatrics.
"Soy products interfere with levothyroxine absorption and endanger infants and young children with congenital hypothyroidism who are at risk for developmental and growth delay," wrote the authors of the case studies.
"When a child is hypothyroid at birth, it's really a medical emergency," said Dr. Brenda Kohn, director of pediatric endocrinology and director of the neonatal thyroid center at New York University Langone Medical Center in New York City. "The impact of soy formula is dramatic in the neonate, and it should be avoided."
Kohn said the issue of soy decreasing the absorption of levothyroxine (brand name Synthroid, among others) is one that's well known to pediatric endocrinologists, but pediatricians and parents may not be as familiar with the potential dangers.
The first case study was an infant girl who was diagnosed with congenital hypothyroidism from the newborn screening test. She was started on levothyroxine when she was six days old. The baby's older brother had been lactose-intolerant, so to avoid that issue the parents started the baby on a soy formula. They gave her levothyroxine about an hour after she had eaten. At three weeks, her pediatrician noticed that the baby had lost weight and didn't have the right muscle tone
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