Levothyroxine: Vitamin Supplement Interactions and Foods to Avoid

Levothyroxine can help control hypothyroidism, but certain supplements and foods may interfere with its efficacy.
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When you have hypothyroidism, your thyroid gland can't make enough of the hormones your organ systems need to function properly.

Many people rely on levothyroxine, a synthetic thyroid hormone, to control this condition, per the Mayo Clinic.

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Certain vitamin supplements that contain specific minerals can interfere with the medication, so it's important to know which products to avoid in order for levothyroxine to work effectively.

Vitamin Supplements to Avoid With Levothyroxine

The 13 essential vitamins include vitamins A, C, E, D, K and the eight B vitamins.

There aren't any studies that report vitamins interact with or affect the absorption of levothyroxine.

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Taking a specific supplement that contains only a single vitamin, such as vitamin D, or one that contains multiple vitamins, such as B complex, should not interfere with how your medication works.

That said, there is one B vitamin —biotin — that can affect blood test results, according to the Mayo Clinic.

Your doctor will perform blood tests to diagnose hypothyroidism and to monitor your blood levels for thyroid stimulating hormones. It is important to let your doctor know if you are taking any type of supplement that may contain biotin.

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Minerals That Interfere With Levothyroxine

Taking a vitamin supplement that also contains minerals, as many do, can pose a problem when also taking levothyroxine.

The minerals calcium, iron, magnesium and aluminum interfere with how your body absorbs levothyroxine, as well as other thyroid hormone replacement medicines and thyroid supplements.

To prevent this, you should not take supplements containing these minerals within four hours of taking your medication, the FDA advises.

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People with hypothyroidism are sometimes told to take iodine supplements to help control thyroid function. This is because an iodine deficiency can cause hypothyroidism. This kind of mineral deficiency is rare in the United States, however, since iodine is often added to salt and other foods, per the Mayo Clinic.

For people who have abnormal thyroid glands, taking too much iodine can worsen hypothyroidism. As with any supplement, it's important to talk with your doctor whether a vitamin supplement containing iodine is safe for you to take.

Safety Warning

One issue with any supplement is that you can't be absolutely sure about all of the ingredients it contains.

The FDA doesn't regulate supplements the same way it does foods. Supplements can be adulterated or mislabeled, but the FDA can take action only after the supplement has reached the market — and that's only if the FDA finds out about a potential problem.

When you're taking a medication like levothyroxine that is so crucial for your body to function properly, it might be better to avoid supplements altogether.

While you may need to supplement with single nutrients to prevent or treat a deficiency when advised by a doctor, taking a daily multivitamin likely isn't necessary. Existing research doesn't show that taking a vitamin supplement is effective for preventing disease.

For example, a December 2013 review of research published in Annals of Internal Medicine that analyzed results of studies involving nearly 400,000 participants did not find any significant evidence of a beneficial effect of vitamin and mineral supplements on heart disease and cancer.

Another study published in ​Annals of Internal Medicine​ in December 2013 concluded that long-term supplementation with a multivitamin had no effect on the cognitive health of the 6,000 male participants enrolled in the trial.

As always, it's best to consult with your health care provider before you decide to take on a vitamin or supplement routine.

Food and Levothyroxine Absorption

In addition to minerals, certain foods may affect the way your body uses levothyroxine. Foods that are high in calcium and iron should be avoided within one hour before or after taking the medication, according to the FDA.

Calcium-rich foods include:

  • Milk
  • Cheese
  • Yogurt
  • Ice cream
  • Cottage cheese
  • Sardines canned with bones
  • Salmon canned with bones
  • Canned shrimp
  • Collard greens
  • Broccoli rabe
  • Kale
  • Soy beans
  • Fortified foods, such as cereal, breads, plant milks and orange juice

Similarly, a calcium supplement — and antacids containing calcium — may interfere with levothyroxine, per the Mayo Clinic.

You'll want to talk options with your doctor before combining levothyroxine and calcium supplements. They may recommend ensuring you take your supplements or antacids at different times than your thyroid hormone replacement.

Iron-rich foods to avoid include:

  • Fortified foods
  • Oysters
  • White beans
  • Dark chocolate
  • Beef liver

Additionally, the Mayo Clinic advises avoiding taking levothyroxine at the same time as walnuts, cottonseed meal, soybean flour and any fiber-rich foods including fruits, vegetables, grains, nuts, seeds and legumes.

Grapefruit and grapefruit juice may also affect the medication's function, per the U.S. Library of Medicine. Because so many foods can affect levothyroxine, it's recommended that you take it on an empty stomach.

Levothyroxine Interactions With Medications

The list of potential drug interactions is lengthy. A partial list provided by the U.S. Library of Medicine includes:

  • Amiodarone (Nexterone, Pacerone)
  • Androgens including nandrolone and testosterone
  • Certain antacids containing aluminum, calcium or magnesium
  • Anticoagulants or blood thinners heparin or warfarin
  • Beta-blockers, such as metoprolol, propranolol or timolol
  • Medications for cancer, such as asparaginase, fluorouracil and mitotane
  • Carbamazepine
  • Clofibrate
  • Corticosteroids, such as dexamethasone
  • Cough and cold medications
  • Weight loss medications
  • Digoxin
  • Medications containing estrogen such as hormone replacement therapy or hormonal contraceptives, for example, birth control pills, patches, rings, implants or injections
  • Furosemide
  • Insulin or other medications to treat diabetes
  • Maprotiline
  • Mefenamic acid
  • Methadone
  • Orlistat
  • Phenobarbital
  • Phenytoin
  • Proton pump inhibitors, such as esomeprazole
  • Lansoprazole
  • Omeprazole
  • Rifampin
  • Sertraline
  • Simethicone
  • Sucralfate
  • Tamoxifen
  • Tyrosine kinase inhibitors, such as cabozantinib
  • Tricyclic antidepressants, such as amitriptyline

Tell your doctor if you are taking any medications, especially those on this list.

Because some of these medications are necessary for certain conditions; rather than stopping the medication, your doctor can adjust your levothyroxine dosage and monitor you for side effects.

Healthy Diet for Hypothyroidism

Aside from avoiding certain foods close to the time when you take levothyroxine, there isn't a specific diet for hypothyroidism, according to Mayo Clinic. Your diet is of supreme importance, however, because it can bolster your health and wellbeing and make taking a vitamin supplement unnecessary.

For the most part, healthy diet looks the same, whether you have hypothyroidism or not. Most important, you should avoid non-nutritive junk food and drinks that are high in sugar and made with refined grains.

Fatigue and weight gain are prominent symptoms of hypothyroidism; ditching these unhealthy foods can help you control your calorie intake and prevent blood sugar spikes and crashes that often result from eating heavily processed foods.

One way you can naturally start to reduce your consumption of these unhealthy foods is to add more nutritious foods to your diet. This often effectively "crowds out" junk foods. Focus on eating more fresh fruits and vegetables, lean meat, poultry, fish, eggs, beans, low-fat dairy, nuts and seeds.

Just be careful not to eat foods high in iron, calcium or magnesium within one hour of taking your medication. While you may have to take levothyroxine for life, you can dramatically improve your overall health and wellbeing with a nutritious diet.

Weight Loss With Levothyroxine

A sluggish thyroid doesn't produce enough hormones; as a result your metabolism slows down, which can easily lead to weight gain. Once you begin to take levothyroxine, your metabolism will normalize and weight loss should hopefully be easier.

Beyond focusing on diet, you can also keep your metabolism high by burning more calories through exercise — especially strength training exercises, which build muscle mass.

Increasing your ratio of muscle to fat will enable you to burn more calories, even at rest, according to February 2009 research in ​Medicine and Science in Sports and Exercise​.

You may also want to increase the amount of protein you consume each day in order to increase muscle mass, per the American College of Sports Medicine.

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