Thyroid medications like levothyroxine are used to treat hypothyroidism, an endocrine disorder where the thyroid gland does not produce enough thyroid hormone. Levothyroxine replaces the deficient thyroid hormone and brings blood levels back to normal. However, levothyroxine absorption can be affected by certain medications, supplements, and even some foods. Knowing what vitamins and supplements to avoid when taking thyroid medication is important for maintaining proper thyroid hormone levels.
Should I avoid all vitamins when taking thyroid medication?
No, not all vitamins need to be avoided when taking thyroid medication. However, some vitamins and supplements can interfere with levothyroxine absorption or alter thyroid hormone levels. The most important vitamins and supplements to avoid include:
- Calcium
- Iron
- Multivitamins containing iron or calcium
- Fiber supplements
- Soy products
- Some herbal supplements like St. John’s Wort
Always check with your doctor or pharmacist before taking any new vitamins, minerals, or herbal supplements with thyroid medication. Let them know about any other medications you take as well.
Why do some vitamins and supplements interfere with thyroid medications?
Certain vitamins and supplements can interfere with thyroid medication absorption for a few reasons:
- They may bind to levothyroxine in the gut, preventing its full absorption into the body. This is the case with calcium, iron, fiber, and soy.
- They can affect how levothyroxine is metabolized and cleared by the liver. For example, St. John’s Wort speeds up levothyroxine clearance.
- Some contain hormones or compounds that may alter thyroid function if taken in large amounts. This includes iodine, selenium, and herbs like ashwaghanda.
Over time, these interactions could make thyroid medication less effective or cause thyroid hormone levels to fluctuate if doses are not adjusted properly.
Vitamins and supplements to avoid with thyroid medications
Let’s take a more in-depth look at some of the key vitamins and supplements to avoid when taking medications like levothyroxine for hypothyroidism:
Calcium
Calcium supplements are one of the most important vitamins to avoid when taking thyroid medication. Calcium can bind to levothyroxine in the gut, preventing its full absorption.[1] Avoid taking calcium supplements or antacids containing calcium within 4 hours of your thyroid medication dose.
Food sources high in calcium like milk, yogurt, and cheese do not cause the same degree of interaction. Just avoid taking thyroid medication at the same time as a calcium-rich meal.
Iron
Iron can also impair levothyroxine absorption when taken at the same time.[2] Avoid iron supplements or multivitamins containing iron for at least 4 hours after taking your thyroid pill.
Fiber supplements
Fiber supplements like psyllium or guar gum can bind levothyroxine in the gut, reducing absorption. Take fiber supplements at least 4 hours apart from thyroid medications.[3]
Soy products
Soy contains compounds called isoflavones that may interfere with thyroid function in sensitive individuals. Avoid large amounts of soy protein and soy supplements.[4]
St. John’s Wort
This popular herbal supplement speeds up the breakdown of thyroid hormones in the liver. It may potentially lower thyroid hormone levels. Avoid routine use while taking thyroid medication.[5]
Other supplements that may interact with thyroid medication
Here are some other vitamins, minerals, and supplements that may potentially impact thyroid medication effectiveness:
- Multivitamins containing iron, calcium or soy isoflavones
- Probiotics – may slightly reduce absorption
- Magnesium – may bind levothyroxine at high doses
- Raspberry ketones – avoid high dose supplements
- Biotin – very high doses may affect lab tests
- Iodine/kelp supplements
- Ashwaghanda
- Selenium
Again, check with your doctor before taking any of these supplements regularly while on thyroid medication. Monitor your symptoms and follow up with thyroid blood work as needed to ensure your medication dose remains optimal.
Safe vitamins to take with thyroid medications
So which vitamins and supplements are safe to use when taking levothyroxine or other thyroid drugs? Here are some good options that should not interact significantly:
Vitamin D
Many people taking thyroid medications are deficient in vitamin D. Supplementing with vitmain D is generally considered safe and helpful for those with hypothyroidism. One study found vitamin D supplementation helped normalize thyroid hormone levels in those with deficiencies.[6]
B complex vitamins
B vitamins play a key role in thyroid hormone synthesis and metabolism. Patients being treated for hypothyroidism often benefit from taking a good B complex vitamin. This includes B12, folate, B6, riboflavin and thiamine. Just avoid B complexes containing biotin in very high doses.
Vitamin C
There are no known interactions between vitamin C supplements and levothyroxine. Taking vitamin C is beneficial for thyroid health and hormone synthesis.[7]
Fish oil/omega-3s
Omega-3 fatty acids from fish oil support healthy thyroid cell membrane function. Fish oil supplements do not interfere with absorption or metabolism of thyroid drugs.[8]
Magnesium
Magnesium helps convert T4 thyroid hormone into the active T3 form. Supplementing with reasonable doses of magnesium citrate or glycinate can be helpful but avoid taking mega-doses.[9]
Probiotics
While probiotic supplements can slightly reduce levothyroxine absorption, this effect is generally insignificant. Probiotics support healthy gut function which is important for proper thyroid hormone metabolism.[10]
Zinc, selenium, copper
Getting adequate trace minerals is essential for thyroid hormone production. Zinc, selenium and copper supplements do not interfere with thyroid drugs as long as dosing is reasonable.
Always discuss supplement use with your doctor and have blood nutrient levels tested regularly when taking thyroid medication.
Tips for taking vitamins safely with thyroid medication
Here are some tips for taking vitamins, minerals and supplements safely when you are on thyroid medication:
- Take thyroid medication first thing in the morning on an empty stomach with water only; wait at least 30-60 minutes before eating or taking other medications and supplements.
- Avoid calcium, iron and fiber supplements for at least 4 hours after taking your thyroid pill.
- Check ingredient labels carefully to make sure multivitamins or other supplements do not contain problematic ingredients like calcium or iron.
- Inform your doctor about any supplements you take regularly so your thyroid blood levels can be monitored.
- Take your thyroid medication 4 hours before or after eating soy products or other foods that may potentially impair absorption.
- Consider having vitamins levels like vitamin D, B12 checked and supplement if deficient.
- Don’t take high doses of potentially problematic supplements like St. John’s Wort, iodine, selenium or iron unless approved by your doctor.
Following these recommendations will help ensure you avoid vitamin-medication interactions while still getting nutrients that support thyroid health.
Which foods should I avoid when taking thyroid medication?
In addition to avoiding certain vitamin and mineral supplements, there are some foods that can impair the absorption of thyroid medication when consumed in large amounts. Foods to avoid close to the time of taking your thyroid pill include:
Soy foods
As mentioned earlier, compounds in soy like isoflavones can potentially impact thyroid function. Avoid large amounts of soybeans, edamame, tofu, soy milk, and soy protein powder.
Dairy products
While small amounts of dairy are fine, avoid consuming things like milk, yogurt, and cheese in large quantities shortly before or after taking levothyroxine. Wait at least an hour if possible.[11]
Fiber supplements
Psyllium husk, wheat bran, and other sources of fiber can impair medication absorption. Avoid taking fiber supplements within 4 hours of your thyroid pill.
Calcium-fortified products
Avoid calcium-fortified orange juice, cereals, or other products when taking thyroid medications.
Coffee
While modest coffee intake is likely fine for most people on thyroid drugs, avoid drinking more than 1-2 cups close to the time you take your pill. Large amounts of coffee could potentially affect absorption.[12]
Iron-rich foods
Foods high in iron like red meat, spinach, and iron-fortified cereals can impair levothyroxine absorption when consumed in large amounts. Avoid eating these foods in excess near the time of taking your medication.
Foods that support thyroid function
While some foods need to be limited around the time you take your thyroid pill, many foods can help support healthy thyroid function when included regularly in moderation as part of a balanced diet:
Nuts and seeds
Nuts and seeds provide selenium, zinc, and healthy fats that support thyroid hormone synthesis. Examples include Brazil nuts, walnuts, sunflower seeds and flaxseed.
Seafood
Fatty fish like salmon provide anti-inflammatory omega-3 fats and are a good source of iodine which is needed for making thyroid hormone.
Berries
Berries are packed with antioxidants like anthocyanins that help reduce inflammation and promote thyroid health.
Cruciferous vegetables
Broccoli, Brussels sprouts, kale and cauliflower are rich in nutrients that enhance thyroid function like iodine, selenium, and zinc.
Avocados
Avocados provide healthy monounsaturated fats to support the thyroid gland.
Chia seeds and hemp seeds
These seeds offer protein, fiber and alpha-linolenic acid, an anti-inflammatory omega-3 fat that benefits thyroid health.
Beans and lentils
Legumes are a great source of zinc, a mineral critical for regulating thyroid hormone levels.
The bottom line
While many common vitamins, minerals and supplements can potentially interact with thyroid medication, this doesn’t mean you need to avoid all supplements. With some care, most people taking thyroid drugs can safely take:
- A basic multivitamin without extra calcium, iron or herbs
- Vitamin D, B complex and vitamin C supplements
- Probiotics
- Fish oil or omega-3 supplements
- Magnesium and zinc in moderate doses
Just be sure to leave enough time between taking your thyroid pill and any problematic supplements. Always consult your doctor to determine the right supplement protocol for your unique health needs. Pay attention to any symptoms you experience and communicate with your healthcare provider regularly. With the right precautions, it is possible to get the nutrients you need without interfering with your thyroid medications.