Table of Contents
Introduction
If your physician says you have an underactive thyroid—also called hypothyroidism—you’re not alone. This condition affects millions of adults, especially women over 30.
Whether it’s due to Hashimoto’s thyroiditis, an autoimmune condition, or other causes, the result is the same: a sluggish thyroid that slows down metabolism, drains energy, and can cause a host of frustrating symptoms.
Common symptoms include fatigue, weight gain, dry skin, hair thinning, depression, and feeling cold all the time. Many people take thyroid hormone medication like levothyroxine but still struggle with lingering symptoms.
That’s because medication isn’t the only piece of the puzzle. Your thyroid depends on key vitamins and minerals to work properly. Without these thyroid-supportive nutrients, your body may not make enough hormones or struggle to use them efficiently.
As a pharmacist, I have seen many patients feel better once they address nutrient deficiencies alongside their medication. It’s not about replacing your prescription but helping it work better.
In this article, we’ll walk through the best vitamins for underactive thyroid, how they work, and why they matter—especially if you have Hashimoto’s thyroiditis, the most common cause of hypothyroidism.
Whether you’re looking to optimize your thyroid function naturally or get more from your current treatment plan, understanding the role of micronutrients is a smart place to start.
How Vitamins Affect Thyroid Function
The Link Between Nutrient Deficiencies and Hypothyroidism
Probiotics can enhance the immune system’s function, decreasing the risk of infection d
Your thyroid gland makes two key hormones: T3 (triiodothyronine) and T4 (thyroxine). But creating and converting these hormones doesn’t happen automatically—it requires nutrients like selenium, zinc, iron, and vitamin D.
When your body is low in these vitamins and minerals, it can’t produce enough hormones or convert them into the form your cells need. Even if your blood tests say your hormone levels are “normal,” you might still feel tired or foggy if your body isn’t activating or using them correctly.
Many people with hypothyroidism are low in several of these nutrients—either due to inflammation, poor absorption, restricted diets, or autoimmune thyroid conditions like Hashimoto’s.
Vitamin D deficiency is especially prevalent and may even contribute to the development or progression of autoimmune thyroiditis.
uring pregnancy. Studies show that certain strains of probiotics aid in preventing urinary tract infections (UTIs) and other common infections. Probiotics exert these effects through changes in vaginal and gut microbiota.
Why Medication Alone Might Not Be Enough
Thyroid medications like levothyroxine provide T4, but they don’t correct the underlying nutrient deficiencies that caused or worsened the problem.
If your body can’t convert T4 into T3 or your cells can’t respond to thyroid hormones appropriately, medication alone may not fully relieve your symptoms.
That’s why so many people start looking into natural remedies for underactive thyroid—not to replace their medicine, but to support their thyroid from the ground up.
Optimizing your intake of thyroid-supportive nutrients can help your medication work more effectively and reduce lingering symptoms.
However, you should use supplements carefully and under medical guidance, especially if you have Hashimoto’s or other autoimmune conditions.
8 Essential Vitamins and Minerals for Thyroid Health
While diet is the ideal source of vitamins and minerals to maintain a healthy thyroid, supplements may be necessary in cases of deficiency or increased need. Here are the top nutrients your thyroid depends on, why they matter, and how to get them safely.
1. Selenium (200 mcg/day)
Selenium is one of the best vitamins for underactive thyroid and a key part of any thyroid complex vitamin.
It helps convert T4 to T3 and protects your thyroid from inflammation and oxidative stress. Low levels are common in people with Hashimoto’s and may increase thyroid antibody levels.
🫛 Where to get it: Brazil nuts (just 2–3 a day is enough), tuna, sunflower seeds.
💊 Supplement tip: 200 mcg per day is ideal. Too much can be harmful, so don’t exceed the recommended dose.
2. Zinc
Zinc is one of the best vitamins for underactive thyroid support as it supports T4 to T3 conversion and helps regulate your immune system. Low zinc can make your thyroid sluggish, and deficiency is more common in people with autoimmune thyroid issues.
🌱 Where to get it: Pumpkin seeds, lentils, oats.
💊 Supplement tip: Zinc gluconate or picolinate (15–30 mg/day). Please don’t take it at the same time as your thyroid medication.
3. Vitamin D
Vitamin D, one of the best vitamins for underactive thyroid, is essential for immune health and thyroid function. Low vitamin D levels are strongly associated with both hypothyroidism and Hashimoto’s. It may reduce inflammation in Hashimoto’s and improve thyroid hormone sensitivity.
☀️ Where to get it: Sunlight, fatty fish, fortified plant milk, egg yolks.
💊 Supplement tip: People need 2,000–5,000 IU daily to correct deficiency. Get your blood levels tested first.
4. Iron
Iron helps your thyroid make hormones and supports the conversion of T4 to T3. It also aids in producing thyroid peroxidase, the enzyme that adds iodine to tyrosine residues to make thyroid hormones. Low iron (even without anemia) can make your thyroid less efficient.
🥬 Where to get it: Spinach, quinoa, tofu, lentils.
💊 Supplement tip: Take separately from thyroid meds and calcium. Ideal ferritin levels for thyroid health are above 70 ng/mL.
5. Iodine (only if deficient)
Your thyroid needs iodine to make hormones—but more isn’t always better. In people with Hashimoto’s, too much iodine can worsen symptoms.
🧂 Where to get it: Iodized salt, seaweed, dairy (if tolerated).
💊 Supplement tip: Never take iodine unless a healthcare provider recommends it based on testing. In Hashimoto’s, iodine supplements may trigger flare-ups.
6. Magnesium
Magnesium helps regulate the thyroid-pituitary feedback loop and supports hundreds of enzyme functions, including energy production. It can also help with constipation and sleep—two common issues in hypothyroidism.
Low magnesium has been linked to poor TSH regulation and increased risk of thyroid disorders.
🥑 Where to get it: Almonds, black beans, avocados.
💊 Supplement tip: Magnesium glycinate is gentle and calming. Aim for 300–400 mg/day.
7. Vitamin B12
Many people with hypothyroidism—especially those with Hashimoto’s—are low in B12 due to poor absorption. It is needed for energy, mood, and nervous system health. Symptoms like fatigue, tingling, or brain fog may overlap with low B12.
🥣 Where to get it: Fortified cereals, plant milk (if vegan), or animal products.
💊 Supplement tip: Methylcobalamin is the active form your body can use. A B-complex is helpful if you’re also low in other B vitamins.
8. Vitamin A
Vitamin A helps your body convert T4 to T3 and supports healthy skin, vision, and immune balance—some people with hypothyroidism struggle to convert beta-carotene into active vitamin A.
🫑 Where to get it: Carrots, sweet potatoes, red peppers.
💊 Supplement tip: If using a supplement, don’t overdo it. Beta-carotene is safer than retinol at high doses.
What to Avoid
Some foods and supplements can interfere with thyroid function
Raw Cruciferous Vegetables (Goitrogens)
Broccoli, cabbage, and kale contain goitrogens, which can affect iodine uptake in large amounts—especially if eaten raw. Light cooking (like steaming) reduces this risk and makes them safer for people with hypothyroidism.
Cooking deactivates most goitrogens, so lightly steaming these vegetables is recommended.
Too Much Iodine
More iodine doesn’t mean better thyroid health. Too much—especially from kelp or seaweed supplements—can worsen Hashimoto’s. Only take iodine if recommended based on lab results.
Iron and Calcium at the Wrong Time
Both iron and calcium can block your thyroid medication. Always take your levothyroxine on an empty stomach, at least 30–60 minutes before eating, and 4 hours away from iron or calcium supplements.
Frequently Asked Questions
No. Vitamins for hypothyroidism support your thyroid but don’t replace the hormone your body can’t make. Always continue your medication unless your doctor tells you otherwise.
There’s no single “best,” but selenium and vitamin D have the most research behind them. They may reduce thyroid antibodies and support immune health.
It depends on your levels. Most people notice improvements in symptoms within 4 to 8 weeks of correcting a deficiency, but this varies depending on the nutrient, the severity of the deficiency, and whether you use thyroid medication. You should recheck your blood levels of nutrients like vitamin D, iron, and B12 after 8–12 weeks to track progress.
Final Thoughts For You
Medication is essential when managing an underactive thyroid, but it’s not the whole story. The best vitamins for underactive thyroid can make a real difference in how you feel by helping your body make, convert, and use thyroid hormones more effectively.
Think of them as tools to support your thyroid—not magic pills. A well-rounded diet, strategic supplements, and regular check-ins with your doctor or pharmacist can help you feel more energized, focused, and in control.
Remember: Hashimoto’s and hypothyroidism are manageable. You’re not alone—and with the correct information and support, you can feel better.
NIH: Hashimoto’s disease – niddk. National Institute of Diabetes and Digestive and Kidney Diseases.
NHS: Levothyroxine: a medicine for an underactive thyroid (Hypothyroidism). nhs.uk.
Endocrine Society: Thyroid and parathyroid hormones.
EBSCO: Natural treatments for hypothyroidism | ebsco research starters.
Morley JE, Russell RM, Reed A, Carney EA, Hershman JM. The interrelationship of thyroid hormones with vitamin A and zinc nutritional status in patients with chronic hepatic and gastrointestinal disorders. Am J Clin Nutr. 1981;34(8):1489-1495.
Benites-Zapata VA, Ignacio-Cconchoy FL, Ulloque-Badaracco JR, et al. Vitamin B12 levels in thyroid disorders: A systematic review and meta-analysis. Frontiers in Endocrinology. 2023;14:1070592.
Farebrother J, Zimmermann MB, Andersson M. Excess iodine intake: sources, assessment, and effects on thyroid function. Ann N Y Acad Sci. 2019;1446(1):44-65.
Zamfirescu I, Carlson HE. Absorption of levothyroxine when coadministered with various calcium formulations. Thyroid. 2011;21(5):483.
