please note: Infants of breastfeeding smokers living in areas of mild to
moderate iodine deficiency are at higher risk of iodine deficiency compared
with infants of breastfeeding nonsmokers.



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

Learning Objectives
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.
Clinical Context
Worldwide, iodine deficiency is the main cause of preventable brain damage
and mental retardation. Lack of thyroid hormone for more than a few weeks
during brain development in utero or during the first years of life may
permanently damage brain function. In 2001, 50 million children were born
in areas without protection against iodine deficiency according to a report
in a 2002 issue of the Bulletin of the World Health Organization by de
Benoist and Clugston.

Thyroid hormones required for fetal brain development are of maternal
origin. Fetal thyroid hormones increase from the second trimester to after
birth to account for brain development in infancy. Maternal milk
concentrates iodide to allow for adequate iodine use by the infant. It is
postulated that the chemical thiocyanate accumulates in the blood of
smoking mothers and competitively inhibits iodide transport in the mammary
gland and ultimately into the infant thyroid gland. This can lead to iodine
deficiency in the infants. Reduction in tobacco smoking and eradication of
brain damage due to iodine deficiency are both World Health Organization
(WHO) goals.

This study assessed the risk of iodine deficiency in breastfed infants
associated with smoking in their mothers, in a population with mild to
moderate iodine deficiency (prior to national salt iodization). The authors
hypothesized that smoking would be associated with reduced iodine content
in smoking mothers' milk and in their infants' urine. The limit for iodine
deficiency used in the study was an iodine concentration in breast milk or
urine of 50 µg/L or less, which has been shown in populations at risk of
iodine deficiency, according to WHO's International Council for the Control
of Iodine Deficiency Disorders' 2001 assessment.

Study Highlights
Healthy pregnant women consecutively admitted for normal vaginal delivery
to hospitals in 5 cities were classified as smokers (n = 50) or nonsmokers
(n = 90) by serum and urine cotinine levels measured during and after
labor.
Inclusion criteria were history of stable iodine intake, intention to
breastfeed, lack of goiter or thyroid disease, and uncomplicated pregnancy.
Women were white and lived in areas of moderate iodine deficiency (smokers,
74%; nonsmokers, 81%; P = .32). In both groups, mean age was 27 years;
parity, 1.5; serum TSH was normal; and gestation was 40 weeks.
Blood samples were taken from the mothers after admission. Umbilical cord
blood sampling occurred shortly after delivery. On day 5 after delivery,
morning spot urine and breast milk samples were collected from the mothers
and a urine sample from neonates.
The study had 80% power to detect a difference in iodine content of 15% to
20% at a 5% level of significance between smoking and nonsmoking mothers.
Smoking and nonsmoking mothers had similar intakes of iodine supplements
and levels of iodine urine excretion.
Neonates born of smoking mothers had significantly lower birth weight
compared with neonates of nonsmoking mothers (mean weight, 3,346 g vs.
3,617 g; P = .001).
Smoking mothers had significantly higher thiocyanate levels in venous and
cord blood compared with nonsmoking mothers (mean serum level, 84.9 µmol/L
vs. 54.7 µmol/L, Pearson's correlation, r = 0.66; P < .001).
Breast milk iodine level was significantly reduced in smoking (mean, 26.0
µg/L) compared with nonsmoking (mean, 53.8 µg/L) mothers (P < .001).
Infants of smoking mothers had lower urinary iodine excretion (mean, 33.3
µg/L) compared with infants of nonsmoking mothers (mean, 50.4 µg/L) with P
= .005.
Smoking was not associated with mothers' urinary iodine excretion but was
negatively associated with mothers' breast milk iodine content (P < .001).
Overall, smoking mothers had much lower breast milk iodine content and
their infants had lower urinary iodine excretion than expected from the
mothers' urinary iodine excretion. The ratio of iodine in infants' urine to
iodine in mothers' milk was significantly higher when the mother was a
smoker.
Pearls for Practice
Infants of breastfeeding smokers living in areas of mild to moderate iodine
deficiency are at higher risk of iodine deficiency compared with infants of
breastfeeding nonsmokers.
Iodine supplementation should be considered for breastfeeding women who
smoke.

             ***********************************************

To temporarily stop your subscription: set lactnet nomail
To start it again: set lactnet mail (or digest)
To unsubscribe: unsubscribe lactnet
All commands go to [log in to unmask]

The LACTNET mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software together with L-Soft's LSMTP(R)
mailer for lightning fast mail delivery. For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html