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Concurrent milk ingestion may affect oral levothyroxine absorption
ORLANDO, Fla. — Patients using levothyroxine should be advised against taking their thyroid hormone replacement therapy simultaneously with cow’s milk, as concurrent ingestion may reduce absorption of the medication, according to new data presented at the Endocrine Society Annual Meeting.
“This study is the first to show that drinking cow’s milk at the same time as taking levothyroxine reduces the absorption of the medication. The findings support previous literature showing the interference of calcium supplements with levothyroxine absorption,” Deborah Chon, MD, an endocrinology fellow at UCLA David Geffen School of Medicine, said during a press conference.
The small study included 10 healthy volunteers who were free of known thyroid disease and had normal thyroid-stimulating hormone concentrations at baseline. Participants also did not have allergies to cow’s milk or levothyroxine and were not pregnant or using oral contraceptives. The mean age was 33 years, and 60% were men.
Levothyroxine absorption with and without coadministration of 12 oz of 2% cow’s milk was measured during two study visits separated by a 4-week washout period.
After an overnight fast, serum total thyroxine concentrations were measured at baseline and at 1, 2, 4 and 6 hours after oral levothyroxine alone or with cow’s milk.
Over the 6-hour study period, the mean total T4 was significantly lower after concurrent ingestion of milk and levothyroxine compared with levothyroxine alone (mean area under the curve, 67.26 ± 12.13 vs. 73.48 ± 16.96; P = .02), according to results reported here. Chon also said peak thyroid hormone levels were significantly lower after concurrent coadministration (P = .04).
On the basis of these findings, the researchers concluded that “patients managed with thyroid hormone replacement therapy should be advised to avoid taking levothyroxine simultaneously with cow’s milk,” Chon said during the press conference.
Levothyroxine is a commonly used medication for patients with hypothyroidism and thyroid cancer. In 2014, more than 120 million prescriptions were written for levothyroxine in the United States, according to Chon.
Levothyroxine is, at most, 70% absorbed through the gut, she said.
“Several studies have shown that certain foods and medications, such as calcium supplements, can interfere with levothyroxine absorption,” Chon said.
For this study, the researchers evaluated the potential effect of cow’s milk, which contains approximately 450 mg of calcium per 12-oz serving. Future research involving other types of milk is warranted, as there are various types and differing calcium contents, she said.
Further studies should also be conducted to “understand at which timepoint there is no [longer an] effect of milk on levothyroxine,” she said.
Also, additional studies should be conducted to “understand at which timepoint there is no [longer an] effect of milk on levothyroxine,” she said. – by Katie Kalvaitis
Reference:
Chon D, et al. LB-SUN-25. Presented at: The Endocrine Society Annual Meeting; April 1-4, 2017; Orlando, Fla.
Disclosures: The researchers report no relevant financial disclosures.
Perspective
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About 50% to 60% of adults aged older than 20 years consume milk, on average three-quarters of a cup per day. Given that levothyroxine is one of the most prescribed medications in the United States, it is likely that many milk consumers are also receiving levothyroxine. For these patients, understanding whether concomitant ingestion of thyroid replacement therapy with milk is adequate is important.
Chon and colleagues investigated the absorption of levothyroxine with and without cow’s milk ingestion (12 oz of 2% fat milk = 450 mg of elemental calcium) in 10 healthy patients (mean age, 34 years; 60% men). They found less levothyroxine absorption in patients exposed to cow’s milk than in patients that were not exposed (mean area under the curve [AUC] of serum total T4 was significantly lower at 67 vs. 73 respectively; P = .02).
The results of this study reinforce previous reports in which levothyroxine absorption is decreased with calcium supplements, medications and food. Patients and clinicians could use this information to make better informed decisions about whether cow’s milk should be avoided during levothyroxine administration. Ideally to decrease overutilization of levothyroxine and to optimize levothyroxine absorption, milk should be avoided at the time of administration of levothyroxine. In those patients that highly value milk intake, dose adjustment might be needed.
- Nicole Iñiguez-Ariza, MD