In the assessment, nine out of ten had detectable amounts of T3 hormone, and five of the ten contained T4. Half the supplements studied, if taken at the recommended dose, delivered T3 quantities greater than 10 mcg a day, and four delivered T4 dosages ranging from 8.57 to 91.6 mcg/day.
The researchers concluded that these supplements can potentially alter patients' thyroid levels significantly, and even cause "iatrogenic thyrotoxicosis" (hyperthyroidism induced by overexposure to ingested thyroid hormone).
A few key points relevant to thyroid patients:
- Nine out of ten products had detectable T3, ranging between 1.3 mg to 25.4 mcg per tablet.
- Five of the supplements, if taken at the manufacturer's recommended dose, delivered T3 from 5.5 to 25.4 mcg/day
- Five products had detectable levels of T4 ranging from <0.5 to 22.9 mcg per tablet.
- Taken at the recommended dose, one of the products delivered more than 25 mcg (.25 mg) of T4 per day.
- Five of the products contained detectable T3 and T4.
- One of the products labeled as "bovine" raw thyroid had no detectable T3 or T4.
- All of the products contained varying levels of iodine.
- All five of the "herbal" supplements contained detectable amounts of T3, and two of them had detectable levels of T4, indicating that raw thyroid has been added to them, but not reflected in the ingredients list.
Grace Y. Kang, et. al. "Thyroxine and Triiodothyronine Content in Commercially Available Thyroid Health Supplements." Thyroid. June 2013, ahead of print. Abstract.