Breast milk contains too little thyroid
hormone to raise plasma thyroid hormone concentrations in preterm
infants
(July 2002)
The background of
the study. Breast milk may contain small amounts of thyroxine
(T4) and triiodothyronine (T3). In this study plasma T4 and T3 concentrations
were measured at multiple times in breast-milk-fed and formula-fed
preterm infants.
How the study was done. The study
subjects were preterm infants who were part of the control group
of a study of the effect of T4 therapy on postnatal development.
The infants were given decreasing amounts of intravenous feedings
and increasing amounts of oral feedings starting at birth; by two
weeks most infants received only oral feedings of expressed breast
milk or formula. The infants were divided into breast-milk- and
formula-fed groups on the basis of the daily intake of breast milk
in relation to total intake. The breast milk group received >50
percent of their caloric intake as breast milk; the formula group
received <25 percent of their caloric intake as breast milk.
Plasma T4, T3, and thyrotropin (TSH) were measured on days 7, 14,
21, 28, 35, and 42 after birth in all infants. In addition, T4 and
T3 were measured in samples of milk collected from 32 mothers of
preterm infants and 10 mothers of term infants, and in the formula
used.
The results of the study. There
were 32 infants in the breast milk group and 25 infants in the formula
group. The mean plasma T4, T3, and TSH concentrations were almost
identical at all six times in both groups of infants.
The concentrations of T4 in the milk of the mothers of preterm
infants were very low, as was the concentration in the formula,
and the concentrations were five times higher in the samples from
the mothers of term infants.
The conclusions of the study. Plasma
T4 and T3 concentrations are similar in preterm infants fed breast
milk and formula during the first weeks of life.
The original article. Van Wassenaer
AG, Stulp MR, Valianpour F, Tamminga P, Ris Stalpers C, de Randamie
JS, van Beusekom C, de Vijlder JJ. The quantity of thyroid hormone
in human milk is too low to influence plasma thyroid hormone levels
in the very preterm infant. Clin Endocrinol 2002;56:621-7.
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