Physiology, Laboratory Testing, and Iodine
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Figure 4. Thyroid Hormone and Iodine Content in Breastmilk
Bloodstream Alveolar and ductal epithelial cell
IO–
lactoperoxidase
T1 and T2
breast peroxidase
Prolactin/
estradiol/
oxytocin
NIS
I and I2
BL AP
Milk protein
iodination
Although the World Health Organization suggests a median urinary iodine concentration (UIC)
threshold of >100 mcg/L to indicate adequate iodine nutrition in lactating women, UIC alone
may not fully reflect the iodine status of this group, as UIC tends to be lower in lactating women
compared to non-lactating women, since iodine is excreted both in urine and breast milk. NIS and
Pendrin are expressed in lactating mammary cells and facilitate the uptake of iodine from maternal
circulation into breastmilk.
