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Cow’s milk interferes with absorption of thyroid supplement levothyroxine

Taking the common oral thyroid hormone medication levothyroxine with a glass of cow’s milk significantly decreases the body’s ability to absorb the drug, a preliminary study finds. Results will be presented Sunday at ENDO 2017, the Endocrine Society’s 99th annual meeting in Orlando, Fla.

“These findings support previous research showing that calcium supplements can interfere with levothyroxine absorption,” said principal investigator Deborah Chon, M.D., an endocrinology fellow at the UCLA David Geffen School of Medicine and the VA (Veterans Affairs) Greater Los Angeles Healthcare System, Los Angeles, Calif. “Decreased absorption means that patients may not get the full dose of thyroid hormone that they are prescribed.”

Although it makes sense that milk, which contains calcium, might interfere with levothyroxine absorption, no study has proved that it does until now, according to Chon.

Levothyroxine is prescribed for patients with an underactive thyroid, called hypothyroidism, to replace the natural thyroid hormone thyroxine (T4) that is too low, or for patients with thyroid cancer, to suppress their thyroid stimulating hormone levels. In 2014, levothyroxine was the most commonly prescribed medication in the U.S., a survey from the IMS Institute for Healthcare Informatics (now QuintilesIMS) found.

Chon and fellow investigators studied 10 adults (six men and four women), with an average age of 33.7 years, who had no known thyroid disease and had normal thyroid hormone function at the start of the study. No one was allergic to cow’s milk or levothyroxine, and none of the women were pregnant or using birth control pills.

Participants fasted overnight before each of two study visits, spaced a month apart. At one visit, participants took 1,000 micrograms of oral levothyroxine alone and at the other visit, they took the same dose concurrently with 12 ounces of 2 percent milk. Before dosing and one, two, four and six hours after ingestion of levothyroxine, participants gave blood samples for measurement of their total T4 levels. Chon said they tested with generic levothyroxine, which most of their patients are taking.

The investigators measured the levothyroxine absorption as the concentration of total T4 in the blood plotted on a graphic curve against time after drug administration, called area under the curve. Over the six hours after the participants took levothyroxine, those who consumed milk at the same time as the medicine had significantly lower total T4 absorption than when they took the drug alone: average area under the curve of 67.3 versus 73.5.

The manufacturer of a brand of levothyroxine recommends that the medication be taken preferably on an empty stomach, 30 to 60 minutes before eating food or taking other medications or vitamins.

“The main message of this study is that patients managed with thyroid hormone replacement therapy should be advised to avoid taking levothyroxine simultaneously with cow’s milk, given its interference,” Chon said.

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Congenital Hypothyroidism

The thyroid is a small gland below the skin and muscles at the front of the neck, at the spot where a bow tie would rest.

It’s brownish red, with left and right halves (called lobes) that look like a butterfly’s wings. It weighs less than an ounce, but helps the body do many things, such as get energy from food, grow, and go through sexual development.

What Is Hypothyroidism?

Hypothyroidism (or underactive thyroid) is when the thyroid gland doesn’t make enough of some important hormones. This makes the body use up energy more slowly, and chemical activity (metabolism) in the cells slows down.

Hypothyroidism is a common condition, especially in adult women.

What Is Congenital Hypothyroidism?

Kids can have hypothyroidism too. When a baby is born with it, it’s called congenital hypothyroidism.

Other kids develop it later, usually late in childhood or as teens. Most of these cases are caused by the disease Hashimoto’s thyroiditis.

What Are the Signs & Symptoms of Congenital Hypothyroidism?

Early signs of congenital hypothyroidism in a baby include:

• jaundice (yellow skin or eyes)
• sleeping longer or more often than usual
• constipation
• a large soft spot (fontanel) on the head
• large, swollen tongue
• weak («floppy») muscle tone
• swelling around the eyes
• poor or slow growth
• cool, pale skin
• large belly with the navel sticking out

Without treatment, children with congenital hypothyroidism can develop permanent mental disabilities. They also may have a poor appetite and breathing problems.

What Causes Congenital Hypothyroidism?

Most cases of congenital hypothyroidism happen because the thyroid doesn’t form correctly in the baby during pregnancy. At birth, the baby may have no thyroid gland at all, or have a small, partially developed gland. Why this happens is often unknown, but in some cases it is genetic.

Less commonly, a baby’s thyroid did fully develop, but can’t make normal amounts of thyroid hormone. This is usually due to a genetic problem. Other children born to the same parents have a 1 in 4 chance of having the same thyroid problem.

How Is Congenital Hypothyroidism Diagnosed?

It’s very important to diagnose and treat hypothyroidism right away. So thyroid testing is done on all infants at birth as part of normal newborn screening.

A heel prick blood sample is tested to look for:

• low levels of T4 (thyroxine), a hormone made by the thyroid that helps control metabolism and growth
• high levels of TSH (thyroid stimulating hormone), made by the to stimulate the thyroid and increase its production of thyroid hormones

If the newborn screen test is abnormal, other blood test are done to be sure of the diagnosis. Sometimes doctors order imaging tests, such as an ultrasound or a thyroid scan, to get more information.

How Is Congenital Hypothyroidism Treated?

A child with hypothyroidism will take thyroid hormone to make up for what the thyroid gland can’t make. Most kids need to take the medicine for the rest of their lives.

Some infants are born with temporary hypothyroidism. This can be caused by things such as premature birth, thyroid disease in the mother, or medicines the mother had during pregnancy. This form of hypothyroidism usually goes away by itself in the first weeks or months of life.

How Can I Help My Child?

If your child has hypothyroidism, it’s very important to give the thyroid hormone as instructed by your doctor.

If your child is too young to chew or swallow the pill, crush it and mix it with a small amount of water, non-soy baby formula, or breast milk. Make sure your child drinks all the liquid. Some thyroid hormone pills dissolve more easily in liquids than others, so talk to your doctor if you’re having trouble with this.

Some infant formulas (especially soy formulas), medicines, and mineral supplements (like calcium and iron) may block the thyroid medicine from being absorbed. Check with your doctor about how and when to give other medicines or supplements while your child takes thyroid hormone.

What Else Should I Know?

Your doctor will see your child regularly to make sure that the medicine is working and change the dose as your child grows. Be sure to go to all follow-up doctor visits.

Children with congenital hypothyroidism can sometimes develop hearing problems. If you have any concerns about your child’s hearing or speech development, talk to your doctor.

How Should I Take Thyroid Hormone

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How Should I Take Thyroid Hormone (L-thyroxine)?

What is the best way to take thyroid hormone?

The maintenance of steady and predictable thyroid hormone levels in the blood is essential to health (see normal thyroid hormone levels). Patients with hypothyroidism need to take thyroid hormone by mouth as a medication each day. Dietary habits can influence how the body absorbs thyroid hormone.

Thyroid medication should be taken on an empty stomach, around the same time each day. Afterwards, we recommend avoiding eating or drinking for 30-60 minutes. Most of our patients take thyroid hormone in the morning upon waking. Breakfast, including any coffee or milk, can be eaten 30-60 minutes later. The second most popular method is to take thyroid hormone in the evening, at least 3-4 hours after any food intake. You should try to establish a routine that allows you to be consistent each day.

Certain medications and supplements decrease absorption of thyroid hormone and should be taken 3-4 hours after taking thyroid hormone. These include fiber supplements, calcium and iron supplements, proton pump inhibitors (omeprazole/Prilosec and lansoprazole/Prevacid), soy products, and multivitamins with minerals.

Are certain foods okay? Can I drink coffee with thyroid hormone?

Unfortunately, even coffee can interfere with how you absorb thyroid hormone. We recommend waiting 60 minutes after you take thyroid hormone to drink coffee. If you are having trouble maintaining an empty stomach in the morning, please discuss this issue with your physician.

What happens if I eat or take medication too soon?

If you occasionally do not wait the full recommended time before eating or drinking, do not worry. This is not dangerous. Just do your best the next day.

The recommendations provided here help your doctors to dose your thyroid medication more accurately and decrease the need for frequent blood tests. If you are having trouble taking your thyroid hormone consistently, please speak with your doctor.

Do I have to take my thyroid hormone in the morning? Can I take my thyroid hormone at night?

Taking your thyroid hormone at night is a fine option, but remember that it should be taken on an empty stomach and at least 3-4 hours after eating.

What happens if I miss a dose?

Missing a single dose of thyroid hormone is not dangerous, so please don’t panic! Please ask your doctor what they would like you to do if you miss a dose of thyroid hormone. In many cases, your doctor may ask you to take two doses the next day. In some instances, skipping a dose is okay.

I take biotin as a dietary supplement. May I continue taking it?

Biotin has no effect on the thyroid, but it does interfere with thyroid lab tests. If you are going to have blood tests to check your thyroid function, please stop taking your biotin three days beforehand to have an accurate result.

Schedule an appointment to speak to an endocrinology expert:

Further reading & references

1. “Normal Thyroid Hormone Levels.” UCLA Health.
2. “Thyroid Hormone Treatment” Patient Brochure from American Thyroid Association. https://www.thyroid.org/thyroid-hormone-treatment/
3. “Levothyroxine.” National Health Service. https://www.nhs.uk/medicines/levothyroxine/
4. “Clinical Practice Guidelines for Hypothyroidism in Adults: Cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association.” Garber, Jeffery et al. (2012). https://www.liebertpub.com/doi/full/10.1089/thy.2012.0205
5. “Effects of Evening vs Morning Levothyroxine Intake, A Randomized Double-blind Crossover Trial.” Bolk, Nienke et al. Archives of Internal Medicine. (2010). https://jamanetwork.com/journals/jamainternalmedicine/article-abstract/776486
6. “Altered Intestinal Absorption of L-Thyroxine Caused by Coffee.” Benvenga, Salvatore et al. Thyroid. (2008). https://www.liebertpub.com/doi/abs/10.1089/thy.2007.0222
7. “Concurrent Milk Ingestion Decreases Absorption of Levothyroxine.” Chon, Deborah et al. Thyroid. (2018). https://www.liebertpub.com/doi/full/10.1089/thy.2017.0428
8. “Serum Thyrotropin Levels Following Levothyroxine Administration at Breastfast.” Siilva Perez, Camila Luhm et al. (2013). https://www.liebertpub.com/doi/full/10.1089/thy.2012.0435
9. “Treatment of Hypothyroidism with Once Weekly Thyroxine.” Grebe, Stefan et al. (1997). https://doi.org/10.1210/jcem.82.3.3830
10. “Metformin does not suppress serum thyrotropin by increasing levothyroxine absorption.” Al-Alusi, Mostafa et al. (2015). https://www.liebertpub.com/doi/full/10.1089/thy.2015.0211