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Smoking Reduces Iodine Transport Into Breast Milk

  • Authors:
  • CME Released: 1/23/2004
  • Valid for credit through: 1/23/2005
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Target Audience and Goal Statement

This article is intended for primary care physicians, obstetricians and gynecologists, and other specialists who care for lactating women or their infants.

The goal of this activity is to provide the latest medical news to physicians and other healthcare professionals in order to enhance patient care.

Upon completion of this activity, participants will be able to:

  • Describe the effect of smoking on iodine metabolism of lactating mothers and their breastfeeding infants.
  • Assess the risk of iodine deficiency in infants of smoking mothers.


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  • Laurie Barclay, MD

    Laurie Barclay is a freelance reviewer and writer for Medscape.


    Disclosure: Dr. Barclay has reported no significant financial interests.

CME Authors

  • Désirée Lie, MD, MSEd

    Clinical Professor, Family Medicine, University of California, Orange; Director, Division of Faculty Development, UCI Medical Center, Orange, California


    Disclosure: Dr. Lie has reported no significant financial interests.

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Smoking Reduces Iodine Transport Into Breast Milk


CME Released: 1/23/2004

Valid for credit through: 1/23/2005


Jan. 23, 2004 — Smoking reduces the transport of iodine into breast milk, according to the results of a study published in the January issue of the Journal of Clinical Endocrinology and Metabolism. The investigators suggest that women who breastfeed should not smoke, but if they do, they should have iodine supplementation.

"Lack of iodine for thyroid hormone formation during the fetal stage and/or the first years of life may lead to developmental brain damage," write Peter Laurberg, from Aalborg Hospital in Denmark, and colleagues. "During the period of breastfeeding, thyroid function of the infant depends on iodine in maternal milk."

The investigators used cotinine levels in urine and serum to identify whether healthy pregnant women who were admitted for delivery were smokers (n = 50) or nonsmokers (n = 90). Both groups had identical urinary iodine on the fifth postpartum day, but smoking was associated with reduced iodine content in breast milk (26.0 µg/L vs. 53.8 µg/L; P < .001) and in the infants' urine (33.3 µg/L vs. 50.4 µg/L; P = .005).

Multivariate linear models and logistic regression analysis revealed that the odds ratio for smoking vs. nonsmoking mothers to have lower iodine content in breast milk than urinary iodine content was 8.4 (95% confidence interval, 3.5 - 20.1). In smokers, iodine transfer into breast milk was inversely related to urinary cotinine concentration. Smoking mothers had significantly higher serum levels of thiocyanate, which may interfere with iodide transport in the lactating mammary gland by competitive inhibition of the sodium-iodide symporter.

"Smoking during the period of breastfeeding increases the risk of iodine deficiency-induced brain damage in the child," the authors write. "Women who breastfeed should not smoke, but if they do, an extra iodine supplement should be considered."

J Clin Endocrinol Metab. 2004;89:181-187

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