Levothyroxine: Vitamin Supplement Interactions and Foods to Avoid

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.

Certain multivitamins or 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.

The 13 essential vitamins include vitamins A, C, E, D, K and the eight B vitamins, according to the National Institute on Aging.

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

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 levothyroxine 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.

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, according to the levothyroxine prescribing information.

To prevent this, you should not take supplements containing these minerals within 4 hours of taking your medication, per the FDA.

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, because 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 supplement containing iodine is safe for you to take.

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 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 December 2013 Annals of Internal Medicine study concluded long-term supplementation with a multivitamin had no effect on the cognitive health of the 6,000 participants.

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

In addition to minerals supplements, certain foods may affect the way your body uses levothyroxine. These include soybean flour, cottonseed meal, walnuts, grapefruit and grapefruit juice and fiber-rich foods, according to the FDA.

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.

The medication's prescribing information recommends taking it once daily on an empty stomach, ideally 30 to 60 minutes before breakfast.

The list of potential drug interactions is lengthy. A partial list provided by the 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 and 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.

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

For the most part, a healthy diet looks the same, whether you have hypothyroidism or not. Most importantly, you should avoid less nutritious food and drinks that are higher in sugar or made with more refined grains.

While you may have to take levothyroxine for life, you can improve your overall health and wellbeing with a balanced diet.