How Calcium Can Affect Thyroid Hormone Replacement

What You Need to Know to Get the Benefits of Both

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The low levels of thyroxine created by an underactive thyroid (hypothyroidism) can be treated with synthetic thyroid hormones. These medications, which also are sometimes used as part of treatment for other thyroid conditions, can be a little tricky to take correctly. One reason is a number of supplements are known to interfere with how well they're absorbed by the body. Among these are calcium supplements, which often are recommended to help prevent bone loss and osteoporosis. Some medications, particularly antacids that contain calcium, and calcium-rich foods pose a similar concern.

Understanding the potential for calcium supplements to interfere with thyroid medication is especially important for women who've gone through menopause, as they're at an increased risk for both hypothyroidism and osteoporosis and so may need to juggle taking medication for the former while also taking supplements for the latter.

Man holding pills and glass of milk
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The Effect of Calcium Supplements

There are different types of thyroid medications, as well as a variety of sources of calcium that can interact with them, so it can be helpful to know a bit about each so that you can make informed decisions about the drugs and supplements you take.

Calcium Supplements

There are a number of different calcium compounds. Each contains varying amounts of elemental calcium, which is the actual mineral that's released into the body. Only two types typically are used in supplements.

  • Calcium carbonate, which is 40 percent elemental calcium
  • Calcium citrate, which is 21 percent elemental calcium

Research shows that both types of calcium have a similar impact on the absorption of thyroid medication. One study comparing three types of calcium, including calcium carbonate and calcium citrate, found that each reduced the absorption of levothyroxine equally—by about 20 percent to 25 percent.


Calcium carbonate is the type of calcium used in antacids to relieve indigestion. Some people use antacids as a calcium supplement as well. Familiar brand names of antacids that contain calcium carbonate include Alka-Mints, Caltrate 600, Rolaids, and Tums.

Calcium carbonate also is in a number of combination products, such as Gas-X with Maalox, Rolaids Plus Gas Relief, and Titralac Plus, all of which contain simethicone for relieving gas and bloating.

Food Sources of Calcium

A 2018 study found that subjects who took levothyroxine and drank 12 ounces of 2 percent milk at the same time had significantly lower levels of the thyroid medication in their blood than those who took the drug without milk.

This suggests that if you're taking levothyroxine to treat an underactive thyroid, you should be as careful about eating or drinking foods and beverages that contain significant amounts of calcium as you are with taking calcium supplements.

This doesn't mean, of course, that you should cut back on calcium: Most adults need around 1,000 to 1,200 milligrams each day. Since it's always better to get nutrients from foods rather than supplements, this means including not only milk in your diet but also other dairy products; dark green leafy vegetables like collards and kale; fish with edible soft bones, such as sardines and canned salmon; and calcium-fortified foods and beverages including soy products, cereal and fruit juices, and milk substitutes.

Consuming Calcium When You Take Thyroid Medication

Calcium interferes with hormone medications by preventing them from being fully absorbed into the bloodstream, which is how they're distributed to cells throughout the body. The best way to prevent this from happening is to take calcium and thyroid medication separately and follow a few other simple guidelines:

  • Take your thyroid medication on an empty stomach to enhance how well it's absorbed by your body.

For most people, the best time to take thyroid medication is first thing in the morning, at least 30 to 60 minutes before having coffee or breakfast.

  • Wash your medication down with plain water.
  • Wait 30 minutes to an hour before drinking coffee or eating breakfast.
  • Wait at least four hours to take a calcium supplement or antacid, or to eat or drink a calcium-rich food or beverage.
  • If you prefer to take your thyroid medication later in the day or at night, time it so that at least four hours have gone by since you last ingested calcium in any form.
  • Be consistent: Whether you decide to take thyroid medication in the morning or evening, take it at the same time every day.

Of course, the most important rules to follow if you're taking a thyroid medication are those that your healthcare provider makes when prescribing it. He or she will know what's likely to work best for you and will be able to tweak your medication or help fine-tune your diet if necessary.

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

By Mary Shomon
Mary Shomon is a writer and hormonal health and thyroid advocate. She is the author of "The Thyroid Diet Revolution."