Author Interviews, Pharmacology, Thyroid Disease, UCLA / 07.04.2017
Thyroid Hormone Medication Should Not Be Taken With Cow’s Milk
MedicalResearch.com Interview with:
Deborah Chon MD
Endocrinology fellow
UCLA David Geffen School of Medicine
MedicalResearch.com: What is the background for this study? What are the main findings?
Response: Our study shows that drinking cow's milk concurrently with oral levothyroxine significantly reduces the absorption of the medication.
Levothyroxine is used for the physiologic replacement of thyroid hormone in patients with hypothyroidism and for serum TSH suppression in patients with thyroid cancer. It is the mostly commonly prescribed medication in the United States as of 2014. Frequent dose adjustments of levothyroxine have been shown to be a costly burden to the national healthcare system.
Previous studies have shown that certain foods and medication, such as calcium supplements, can interfere with levothyroxine absorption. However, this is the first study to demonstrate that ingesting cow?s milk, a common breakfast staple, affects oral levothyroxine absorption.
To determine the possible effect of cow's milk ingestion, we measured levothyroxine absorption in humans with and without concurrent milk consumption. Pharmacokinetic studies were conducted in healthy adults without allergies to milk or levothyroxine, and who were not pregnant nor using oral contraceptives. All subjects had no history of known thyroid disease and normal thyroid hormone function at baseline. Following an overnight fast, serum total thyroxine T4 (TT4) concentrations were measured at baseline and at 1, 2, 4, and 6 hours after ingestion of 1,000 ?g of oral levothyroxine alone or when co-administered with 12 oz. of milk (2% fat). There was a four-week washout period between the two study visits.
Ten subjects (mean age 33.7?10.2 years, 60% male) completed the study. The serum total T4 absorption over six hours, calculated as area under the curve (AUC), was significantly lower when taking cow?s milk concurrently with levothyroxine compared levothyroxine alone (mean?SD: 67.26?12.13 vs. 73.48?16.96; p = 0.02). Also, peak serum TT4 concentrations were significantly lower in those who ingested levothyroxine concurrently with milk, compared to taking levothyroxine alone (p=0.04).
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