Oral Levothyroxine Absorption Reduced By Cow’s Milk Consumption

elemental calcium found in cow's milk affects levothyroxine absorption
elemental calcium found in cow’s milk affects levothyroxine absorption
Elemental calcium — found in cow's milk — significantly limits a person's ability to absorb oral levothyroxine.

Patients undergoing therapy with oral levothyroxine should consider avoiding the ingestion of cow’s milk concurrently with the medication, according to study results presented at ENDO 2017: the 99th Annual Meeting & Expo, April 1-4, in Orlando, Florida.1

Following previous studies showing that various foods and supplements can interfere with levothyroxine absorption,2 researchers from University of California, Los Angeles (UCLA)’s David Geffen School of Medicine conducted a study examining the effect of cow’s milk consumption on levothyroxine absorption.

Ten participants with no known history of thyroid disease and normal thyroid stimulating hormone (TSH) levels (mean age: 33.7±10.23; 60% men) took part in the study.

At 2 separate visits, serum total thyroxine T4 (TT4) concentrations were measured following an overnight fast at baseline and again at 1, 2, 4, and 6 hours after drinking 1000 μg oral levothyroxine alone or with 12 ounces of 2% milk.

Over 6 hours, serum TT4 absorption — calculated as the area under the curve (AUC) — was significantly lower in participants who combined oral levothyroxine with milk consumption (mean: 67.26±12.13 vs 73.48±16.96; P =.02).

“This is the first study to demonstrate that concurrent cow’s milk ingestion reduces oral levothyroxine absorption,” the researchers concluded. “The findings support previous literature showing the interference of elemental calcium with oral levothyroxine absorption.”

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  1. Chon D, Reisman T, Weinreb J, Hershman JM, Leuung AM. Concurrent milk ingestion decreases oral levothyroxine absorption. Abstract LB SUN 25. Presented at: ENDO 2017: the 99th Annual Meeting & Expo. April 1-4, 2017; Orlando, Florida.
  2. Zamfirescu I, Carlson HE. Absorption of levothyroxine when coadministered with various calcium formulations. Thyroid. 2011;21(5):483-486.