Aug 1, 2012 by EDITOR
Excess Maternal Iodine Linked to Thyroid Problems in Newborns
Obtaining your iodine from natural sources in food is essential to overall health. However, over supplementation with iodine during pregnancy could lead to the development of congenital hypothyroidism in newborns, according new clinical case data.
In 2005, a team of Italian researchers recommended routine thyroid-function screening for pregnant women due to findings that attention deficit and hyperactivity disorder (ADHD) in children may be associated with an iodine deficiency in mothers. Since then iodine supplementation has risen dramatically. However, one problem is over supplementation.
The research paper -- published in the Journal of Pediatrics -- describes three infants who developed thyroid hormone deficiency (known as congenital hypothyroidism) as a result of excess maternal iodine supplementation.
Dr Kara Connelly of Oregon Health & Science University, USA, and colleagues reveal the details of three infants with congenital hypothyroidism whose mothers had taken 12.5 mg of iodine daily -- more than 11 times the safe upper limit -- while pregnant and/or breastfeeding.
"The use of iodine-containing supplements in pregnancy and while breastfeeding is recommended," noted Connelly. "However, these cases demonstrate the potential hazard of exceeding the safe upper limit for daily ingestion."
Connelly and her colleagues called for increased attention a potential increase in the use of nutritional supplements containing iodine in amounts far higher than the recommended daily allowance during pregnancy: "The use of nutritional supplements is increasing in our society due to the belief that they are healthy and safe and can replace dietary deficiencies with minimal side effects."
"The mothers of these three infants were ingesting a nutritional supplement whose iodine content far exceeded the daily recommended intake and had elevated iodine levels in urine and breast milk samples."
Connelly and her team revealed that the three infants had blood iodine levels 10 times higher than healthy control infants.
They added that although the World Health Organization (WHO) recommends 200-300 micro grams of iodine daily during pregnancy for normal fetal thyroid hormone production and neurocognitive development, 1,100 micro grams is considered to be the safe upper limit for daily ingestion by the US Institute of Medicine.
Globally congenital hypothyroidism is most commonly caused by a deficiency of iodine. However excess iodine may also be part of the explanation for the reported increasing incidence in recent years.
However, the team noted that because it is not routine practice to ask mothers of infants with congenital hypothyroidism about all nutritional supplements taken during pregnancy, the over-supplementation of iodine -- leading to excess iodine -- may be a more common practice than currently presumed.
Journal of Pediatrics