Milk reduces absorption of thyroid supplement levothyroxine

Last Updated: 2017-04-03

By Megan Brooks

NEW YORK (Reuters Health) – Taking levothyroxine with a glass of cow’s milk significantly decreases absorption of the thyroid medication, new research shows.

“Patients managed with thyroid hormone should be advised to avoid drinking cow's milk simultaneously when taking levothyroxine,” said principal investigator Dr. Deborah Chon, an endocrinology fellow at the UCLA David Geffen School of Medicine in Los Angeles, California.

Dr. Chon reported the results April 2 at ENDO 2017, the Endocrine Society’s 99th annual meeting in Orlando, Florida.

Levothyroxine is largely absorbed through the gut. While past research has shown that calcium supplements can interfere with levothyroxine absorption, this is the first study to specifically investigate the effect of concurrent milk ingestion on levothyroxine absorption, she explained at a press briefing.

Dr. Chon and colleagues measured levothyroxine absorption with and without concurrent milk consumption in six men and four women (mean age, 33 years). All participants were healthy, with no history of known thyroid disease and a normal serum TSH concentration at baseline.

Following an overnight fast, serum total thyroxine T4 (TT4) concentrations were measured at baseline and at one, two, four and six hours after ingestion of 1000 mcg of oral levothyroxine alone or when co-administered with 12 ounces of 2% milk. There was a four-week washout period between the two study visits.

The serum total T4 absorption over six hours was significantly lower in those who drank milk with levothyroxine, compared to those who took levothyroxine in the absence of milk (mean area under the curve 67.3 vs. 73.5, P=0.02).

“Decreased absorption means that patients may not get the full dose of thyroid hormone that they are prescribed,” Dr. Chon said in a conference statement.

It is currently recommended that levothyroxine be taken preferably on an empty stomach, 30 to 60 minutes before eating food or taking other medications or vitamins.

Reached for comment, Dr. Linda Werner, of Endocrine Associates LLC in Bridgeport, Connecticut, told Reuters Health, “It's not surprising that taking levothyroxine with milk decreases the absorption and changes thyroid levels. The absorption of levothyroxine is decreased when taken with food, but also when taken with things like calcium or iron, so not surprising when you give it with milk that you change the absorption.”

“The change in levels is real but not usually enormous,” Dr. Werner said by email. “The best way to take levothyroxine is on an empty stomach 30 minutes before meals, but having said that, levothyroxine is often a medication that people are on for many years (often indefinitely) and some people have a hard time always taking it on an empty stomach. What I tell my patients is that if taking it on an empty stomach works for them, great, but if not, the most important thing about taking levothyroxine is to take it the same way every day. In other words, if they need to take it closer to a meal, fine, but make that your routine. That way, we adjust the dose to take into account the decreased absorption. What they don't want to do is take it on an empty stomach for several weeks, then start taking it with food or milk for a few weeks (then you have difficulty controlling the levels),” Dr. Werner noted.

SOURCE: http://bit.ly/2oQvJVe

ENDO 2017.