Screen Shot 2015-06-08 at 10.21.48 AMWhen I, Janie, was nursing my second and third child, I was hypothyroid and didn’t even know it. As a result of combining nursing with untreated hypothyroidism, I was constantly sick with viral infections like colds, the flu, and even pneumonia…each time! That taught me that nursing is demanding on one’s body! This is not to say that every hypothyroid mother will be sick like I was when nursing. But it does underscore that nursing puts more demand on one’s body.

What can being hypothyroid do to a nursing mother’s body and health?

Whether a new mother is undiagnosed hypothyroid as I was, or in some cases, undertreated/poorly treated with thyroid meds like Synthroid or other T4-only meds, there is evidence that the hypothyroidism can cause a lessened production of milk in some women. It didn’t happen to me, but there are first-hand reports from others of it happening. A study done in 2003 by Hapon, Simoncini, Via, et al found that when rats were made hypothyroid, they released much less milk when lactating than did control mothers, “resulting in poor milk transfer and poor litter growth”.

Breastfeeding while hypothyroid can also lower one’s resistance to infections, as I so miserably found out. I was sick every 2-3 weeks while nursing, culminating with pneumonia! Could it be the result of a stressed immune system from the combination of the hypothyroid state and the demands of breastfeeding? I think so. The lack of sleep on top of being hypothyroid didn’t help either. Nutritional needs can be increased as well in hypothyroid mothers due to lowered stomach acid, possibly even more so than for non-hypothyroid lactating moms.

Is a hypothyroid nursing mother dangerous to the baby?

Neither of my two children of whom I nursed while being hypothyroid seemed to suffer. They became healthy and intelligent children and adults, just as much as their oldest sibling did whom I nursed when I didn’t have hypothyroidism. A 2012 book titled “Medications and Mother’s Milk” by Thomas Hale, PhD underscores that even when a nursing mother’s TSH is quite high, it doesn’t pass down via the breast milk to the baby.

As mentioned above, some nursing moms can see a decrease in their breast milk, which in turn can result in poor weight gain in their baby.

Will taking my thyroid medications harm my baby while I’m nursing?

Apparently not. Research shows that the thyroid hormones you take only cross over into your breast milk in minute quantities.

Conversely to being harmed, there are first hand accounts that switching to natural desiccated thyroid can increase one’s breast milk supply, which in turn provides better nutrition to the growing baby. In the book “Breastfeeding and Human Lactation” by Riordan and Wambach, they state “If replacement therapy of thyroid extract (another name for natural desiccated thyroid)… is adequate, the relief of the symptoms and an increase in the milk supply can be quite dramatic.”

What if I am diagnosed as hyperthyroid, aka Graves disease, when breastfeeding?

When nursing mothers with Graves disease are prescribed anti-thyroid meds like Tapazole (methimazole), PTU (propylthiouracil) or Carbimazole (a precurser to methimazole), studies suggest that they will only be in very small doses in the breast milk. Just in case, Thomas Hale, PhD suggests that your doctor monitor your infant’s thyroid function while you are breastfeeding (he suggests the TSH and T4, but informed patients know it’s more important if it’s TSH, free T3 and free T4). Other studies suggest mothers should refrain from breast feeding when taking these medications.

Is RAI (Radioactive iodine) safe if I am nursing?

Most literature says no, since the RAI can get into your milk and potentially harm the nursing baby’s thyroid. They recommend mothers to stop breast feeding until tests done by your doctor reveal there there is no longer any radioactive iodine in your milk. The same is true for a thyroid scan, which involves an injection of radioactive iodine.

Will the hydrocortisone (HC) (or adrenal cortex) I take for adrenal sufficiency be a problem with breastfeeding?

Research shows that even with mothers who have no adrenal problem and make natural levels of cortisol, there is going to be “some” amount of cortisol in their breast milk with no adverse effects. So opinion seems to be that if the HC being taken is in “physiologic” doses, i.e. doses that simply replace what one’s adrenals are not making, it may do no harm to the baby via the breast milk. Potential problems may occur if one is taking quite high “pharmacological doses” for a long time.

Katie Hinde, an evolutionary biologist at Harvard University in Cambridge, Massachusetts, has explained an interesting observation that “female babies fed on breast milk with relatively high concentrations of cortisol showed behavioral changes, such as irritability, fear, anger and discomfort, which were not shown in sons fed on breast milk with similar concentrations of the hormone.

Bottom line, thyroid patients with proven adrenal insufficiency should be doing their Daily Average Temp taking to find their correct physiologic amount, which would hopefully imitate what healthy adrenal function would be doing anyway, and thus, no harm to the baby when nursing. Your doctor can monitor.

More reading:

The Impact of Thyroid Dysfunction on Lactation

The quantity of thyroid hormone in human milk is too low to influence plasma thyroid hormone levels in the very preterm infant.

La Leche League Int’l article

Abstract: Lactation deficiency rate of 19.2% in study mothers with hypothyroidism despite hormone replacement treatment during pregnancy. Hyperthyroidism also seems to lead to decreased milk production.


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