New study associates excess maternal iodine supplementation with congenital hypothyroidism

July 26, 2012

Congenital hypothyroidism is thyroid hormone deficiency at birth that, if left untreated, can lead to neurocognitive impairments in infants and children. Although the World Health Organization recommends 200-300 µg of iodine daily during pregnancy for normal fetal thyroid hormone production and neurocognitive development, the US Institute of Medicine considers 1,100 µg to be the safe upper limit for daily ingestion. A case series scheduled for publication in The Journal of Pediatrics describes three infants who developed congenital hypothyroidism as a result of excess maternal iodine supplementation.

Kara Connelly, MD, and colleagues from Oregon Health & Science University, Doernbecher Children's Hospital, Boston University School of Medicine, State of Oregon Public Health Laboratory, and Randall Children's Hospital at Legacy Emanuel describe three with congenital hypothyroidism whose mothers had taken 12.5 mg of daily, 11 times more than the safe upper limit, while pregnant and/or breastfeeding. Iodine is transferred from the mother to the infant through the placenta or breast milk. The three infants had blood iodine levels 10 times higher than healthy control infants (measured from newborn screening filter paper).

Excess iodine causes the to temporarily decrease function to protect against hyperthyroidism (Wolff-Chaikoff effect). Adults and older children are able to "escape" from this effect after several days of excess iodine to avoid hypothyroidism. However, the immature thyroid glands of fetuses and newborns have not developed this protective effect and are more susceptible to iodine-induced hypothyroidism. Although infants recover normal thyroid function after acute iodine exposure (e.g., a few days of topical iodine application), continuous excessive iodine exposure to the fetal and neonatal thyroid gland may cause long-term harmful effects on thyroid function.

Sources of iodine include , prenatal vitamins, and seaweed (kelp). According to Dr. Connelly, "The use of iodine-containing supplements in pregnancy and while breastfeeding is recommended in the United States. However, these cases demonstrate the potential hazard of exceeding the safe upper limit for daily ingestion." Excess iodine ingestion from supplementation is often unrecognized because it is not routine practice to ask mothers of infants with congenital about nutritional supplements taken during pregnancy. Pregnant or breastfeeding women should discuss the safe dosages of nutritional supplements with their doctors prior to including them in their daily regimen.

Explore further: Researchers urge awareness of dietary iodine intake in postpartum Korean-American women

More information: “Congenital Hypothyroidism Caused by Excess Prenatal Maternal Iodine Ingestion” by Kara Connelly, MD, Bruce Boston, MD, Elizabeth Pearce, MD, David Sesser, David Snyder, MD, Lewis Braverman, MD, Sam Pino, Stephen LaFranchi, MD, appears in The Journal of Pediatrics, DOI 10.1016/j.jpeds.2012.05.057

Related Stories

Researchers urge awareness of dietary iodine intake in postpartum Korean-American women

July 12, 2011
Researchers at Boston University School of Medicine (BUSM) have brought attention to the potential health impacts for Korean and Korean-American women and their infants from consuming brown seaweed soup. Seaweed is a known ...

Harmful effects of hypothyroidism on maternal and fetal health drive new guidelines for managing thyroid disease in preg

July 25, 2011
Emerging data clarifying the risks of insufficient thyroid activity during pregnancy on the health of the mother and fetus, and on the future intellectual development of the child, have led to new clinical guidelines for ...

Recommended for you

Breastfed babies are less likely to have eczema as teenagers, study shows

November 13, 2017
Babies whose mothers had received support to breastfeed exclusively for a sustained period from birth have a 54% lower risk of eczema at the age of 16, a new study led by researchers from King's College London, Harvard University, ...

Obesity during pregnancy may lead directly to fetal overgrowth, study suggests

November 13, 2017
Obesity during pregnancy—independent of its health consequences such as diabetes—may account for the higher risk of giving birth to an atypically large infant, according to researchers at the National Institutes of Health. ...

Working to reduce brain injury in newborns

November 10, 2017
Research-clinicians at Children's National Health System led the first study to identify a promising treatment to reduce or prevent brain injury in newborns who have suffered hypoxia-ischemia, a serious complication in which ...

Why do some kids die under dental anesthesia?

November 9, 2017
Anesthesiologists call for more research into child deaths caused by dental anesthesia in an article published online by the journal Pediatrics.

Probability calculations—even babies can master it

November 3, 2017
One important feature of the brain is its ability to make generalisations based on sparse data. By learning regularities in our environment it can manage to guide our actions. As adults, we have therefore a vague understanding ...

Early childhood adversities linked to health problems in tweens, teens

October 30, 2017
Adverse experiences in childhood—such as the death of a parent, growing up in poverty, physical or sexual abuse, or having a parent with a psychiatric illness—have been associated with physical and mental health problems ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.