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Levothyroxine—Is Morning Still the Best Time to Take It?

If you have hypothyroid, the timing of your levothyroxine will make all the difference between good absorption and not getting the full dosage.

With Angela M. Leung, MD, and Amy Hess-Fischl, MS, RDN, CDE

It has long been known that many foods and medications – including calcium supplements, soy, and iron—interfere with the absorption of oral levothyroxine in the body.1 The plot thickens. For the first time, drinking cow’s milk is demonstrated to reduce absorption of levothyroxine,2 according to a study published in the journal Thyroid.

Levothyroxine is one of the most commonly prescribed medications in the US.3  The findings from this prominent team of researchers at the UCLA David Geffen School of Medicine in California are particularly significant since patients are typically instructed to take levothyroxine an hour before breakfast, a meal that commonly includes dairy.

 “Changes in the amount of levothyroxine absorbed can lead to changes in thyroid blood tests used to monitor the appropriateness of its dose,” says lead author Angela M. Leung, MD, MSc, assistant professor of medicine at the UCLA David Geffen School of Medicine.

Treatment for hypothyroid must be timed to avoid milk. Treatment for hypothyroid must be timed to avoid milk.

Dairy Reduces Levothyroxine Concentration

The study examined 10 healthy subjects with normal thyroid function to assess whether consuming cow’s milk has a direct effect on levothyroxine absorption.2

Following an overnight fast, serum total thyroxine (TT4) concentrations were measured at baseline and at 1, 2, 4, and 6 hours after the participants took 1000 μg of oral levothyroxine alone or when co‐administered with 12 ounces of 2% milk.

Results showed that the TT4 concentrations were significantly lower when levothyroxine was taken at the same time as the milk as compared to levothyroxine alone.2 Also, peak serum TT4 concentrations dropped significantly when cow’s milk was co‐administered with levothyroxine than with the levothyroxine alone.

The researchers believe that both the calcium content of the milk and the presence of protein might directly interfere with the proper and full absorption of levothyroxine, complicating the management of hypothyroid.2

“Our results show that calcium-rich foods should be consumed apart from thyroid hormone medication, as much as possible,” Dr. Leung tells EndocrineWeb. “This will help ensure that thyroid blood tests remain constant, thus decreasing the need for potentially unnecessary changes [increases] in the dose of thyroid replacement needed to manage your hypothyroidism.”

Calcium-rich foods including cow’s milk, yogurt, cheeses (eg, ricotta, cottage, cheddar, American) and ice cream and frozen yogurt. Also, non-dairy milk like those made from almond, soy, and rice, which  are fortified with calcium.4

Worth Considering a Bedtime Switch?

Typically, patients are advised to take their levothyroxine first thing in the morning, at least 30 minutes but preferably an hour before eating, on an empty stomach and with only water.5  The goal is to achieve consistency in taking the medication to avoid fluctuations in thyroid levels and variable control of symptoms.

But for patients who may want to add milk to their morning coffee or cereal, there are alternative dosing strategies, including taking levothyroxine at night.

While not all patients may be candidates for bedtime administration, those who have a consistent sleep routine and don’t take other medications before bed might consider making this switch.

Of course, before you make any change in the timing of when you take your levothyroxine, you should speak to your doctor.  And, it’s important to realize that there must be four hours between your last meal or snack when you plan to take your levothyroxine at bedtime. If you are a nighttime eater, this is likely not a good change for you to make.

Scheduling Timing for Multiple Medications to Avoid Interactions 

Another point in planning for bedtime dosing of your levothyroxine is other medications. Ideally, levothyroxine should be the only medication taken at bedtime. Just as with morning dosing, it is best to avoid co-administration with other medications such as statins, blood pressure drugs, and metformin.

If you must take other medications that must be taken in the evening, consider adjusting the timing of these medications so you take them with dinner, leaving four hours afterward so you can take the levothyroxine at bedtime.

Close monitoring of your thyroid levels and any symptoms you notice will help assure that your thyroid labs remain within acceptable reference ranges.

Determine When Taking Levothyroxine is Best for You

“We have plenty of evidence that taking levothyroxine with a meal decreases its absorption and may lead to variability in TSH levels,” says Amy Hess-Fischl, MS, RD, LDN, BC-ADM, CDE, program coordinator for the Teen and Adolescent Diabetes Transition Program at the University of Chicago’s Kovler Diabetes Center.

“For that reason, it’s recommended to wait 30-60 minutes after taking the thyroid hormone before you have breakfast, particularly for those with thyroid cancer, pregnant women, and those sensitive to thyroid fluctuations.”

“What this study proves is that calcium does affect absorption of levothyroxine, making it inadvisable to take with cow’s milk at the same time,” says Ms. Hess-Fischl.

“For practicality’s sake, patients need to find a schedule to take their levothyroxine at a time that will not be affected by meals – some examples would be right when they get up and wait at least 30-60 minute, or plan to take it four hours after they finish eating for the night, if they are having calcium-containing foods such as milk or ice cream,” she tells EndocrineWeb.

“One thing to say up front is that the drug label on levothyroxine says not to eat or drink for 60 minutes before taking the drug in the morning,” says Anne Cappola, MD, professor of medicine in the division of Diabetes, Endocrinology and Metabolism at the Perelman School of Medicine at the University of Pennsylvania.  She notes that since people tend to continue to eat after dinner, scheduling a dose of levothyroxine in the evening can be as problematic as taking it first thing in the morning.

“It’s also easier to forget to take the medication in the evening,” she tells EndocrineWeb.

Dr. Cappola also points out that the research brings into question what other foods and dietary substances aside from milk, soy, and iron that have yet to be studied that may also interfere with levothyroxine.

Since eating food later in the evening is likely to promote weight gain,6 this is yet another reason to eat more heavily earlier in the day, according to research presented at ENDO 2018, the 100th Annual Meeting of the Endocrine Society.

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