Most people opt to take their thyroid hormone medicine early in the morning, which means they probably take it with orange juice or cow’s milk. Well, a new study reveals that cow’s milk reduces the absorption of thyroid hormone medicines.
One of the most common drugs utilized for the physiologic replacement of the thyroid hormone in the United States is Levothyroxine. Patients that have been diagnosed with serum TSH suppression, a common condition in patients with thyroid cancer, and hypothyroidism will be prescribed Levothyroxine. The national healthcare system has been financially burdened with routine TSH testing and frequent dose adjustments.
For those that have been on a Levothyroxine regimen for some time, will know not to take the medicine concurrently with calcium supplements, because it interferes with the absorption of the medicine. However, this study is the first of its kind to demonstrate that consuming cows milk affects the absorption of Levothyroxine
A team of researchers conducted a study that compared Levothyroxine absorption in people without and with concurrent milk ingestion. Non-pregnant healthy adults (60 percent male) without milk or Levothyroxine allergies and who were not utilizing oral contraceptives volunteered to participate in the pharmacokinetic study. All participants also had normal thyroid hormone function at baseline and no history of thyroid disease. After the participants fasted overnight, the researchers measured their serum total thyroxine or TT4 concentrations at baseline and again at 1, 2, 4 and 6 hours after consumption of 1000 μg of Levothyroxine alone and simultaneously with 12 ounces of 2% milk. A four-week washout period separated the two study visits.
Ten participants completed the study. The serum total T4 absorption over six hours calculated as area under the curve or AUC was much lower when Levothyroxine was ingested with cows milk, compared to when Levothyroxine was ingested alone. The Peak serum TT4 concentrations were also much lower in the participants, who consumed Levothyroxine concurrently with milk as compared to ingesting Levothyroxine alone.
These findings reveal that patients taking a daily regimen of thyroid hormone medicine should be advised to avoid ingesting cows milk concurrently with oral Levothyroxine.
The authors note that future studies would be needed to evaluate the amount of time after the consumption of Levothyroxine in which milk no longer interferes with its absorption. Different types of milk, such as almond milk and soymilk, could also be studied to determine if they have any effect of the absorption of Levothyroxine.