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All-Star Nutrients for Optimal Thyroid Health by Maria "Adi" Benito-Herrero, MD

Updated: Nov 14, 2019

Last week, we reviewed how crucial iodine is to the hormones that regulate our thyroid gland. This week, we're going to learn about which nutrients are most important for our thyroid function. Let's take a look at my patient Barbara's case as a good example.

Barbara was 58 years old when she came to see me because she had been noticing some trouble with her memory. Her doctor had noted that Barbara had high cholesterol. She preferred to eat a vegetarian diet and she rarely ate meat, fish or dairy products. She used sea salt (non-iodized) in her cooking. She was not taking any vitamins or medications.

Barbara’s diet was concerning for low iodine, and her blood test results showed that she was deficient in iron and had low zinc, as suspected from following a vegetarian diet. Her thyroid tests revealed less-than-optimal function. I asked Barbara to start a multivitamin with zinc, selenium and iodine, and I gave her iron supplementation separately. Within months, her thyroid, cholesterol and memory all improved. Barbara's case highlights the importance of nutrients for optimal thyroid performance. This week, we’ll review a few nutrients that are critical to the proper production and function of thyroid hormones: tyrosine, selenium, iron, vitamin A and zinc.

Tyrosine is a non-essential amino acid (this just means that your body can make it). Tyrosine has a number of important functions, including helping your body to produce thyroid hormones. It is also part of your complex of nerve chemicals, and it helps make skin pigment.

Tyrosine is found in chicken, turkey, fish, peanuts, almonds, avocados, bananas, milk, cheese, yogurt, cottage cheese, lima beans, pumpkin seeds and sesame seeds. With the large variety of foods that contain tyrosine, I usually do not have to worry about a deficiency of this nutrient in most of my patients, unless someone is on a very restrictive diet.

Selenium is an essential trace mineral and is important in thyroid health for two reasons: 1) selenium is a cofactor (a helper molecule) in the enzymatic process that converts T4 to T3 (remember that T3 is the active thyroid hormone that performs the necessary thyroid functions); and 2) most importantly, selenium is part of an enzyme complex (such as glutathione peroxidase) that exhibits anti-oxidant and anti-inflammatory effects to the thyroid. In areas of severe selenium deficiency, thyroid disease happens more frequently.

The presence of selenium in foods is determined by the soil content, the use of selenium-containing fertilizers and agricultural practices. If you intend to use a supplement and you live in an area of rich selenium soil, your levels might be higher than ideal. Higher levels and higher intakes of selenium over the long-term have been linked to diabetes and glaucoma.

Still, it is important to ensure there is enough selenium in your diet. Selenium is found in meat and fish, cereal, some nuts and seeds, eggs and shiitake mushrooms. Pork and Brazil nuts top the list of selenium-rich foods. As a practical guide, eating two to three Brazil nuts per day will provide you with about 200 mcg of selenium, the amount that has been used as a thyroid antioxidant in clinical studies. So, go ahead and have a couple of Brazil nuts each day, as long as you have no nut allergies. 

Iron is a cofactor (along with iodine) for the TPO enzyme (thyroid peroxidase), which helps make thyroid hormone. Low iron has been found to cause an enlarged thyroid (goiter), and replenishing iron and iodine together resolves goiters better than adding iodine without the iron. A recent study noted that low iron might be a risk factor for the development of autoimmune thyroid disease (Hashimoto’s thyroiditis)—so, getting adequate iron through our diet is critical; especially during times of growth, and in women, during menstrual years and during pregnancy.

Iron is found in dark animal meats, green leafy vegetables, legumes, dried fruit, seafood and in iron-fortified foods such as cereal, bread or pasta.

  • When using a vegetarian source of iron, add some vitamin C-rich foods (e.g., citrus fruits, tomatoes, pineapple and strawberries) to increase its absorption.

  • When preparing beans, soak them before cooking to allow the iron to be more easily absorbed.

Zinc is important for normal thyroid hormone production and for the conversion of T4 to T3, the active thyroid hormone in our cells. Higher zinc levels result in a reduction in the size of goiters (large thyroid glands) with thyroid nodules. Zinc also has a role in T3 production.

Zinc is a mineral that can be found in yeast, whole grains, nuts (almonds, peanuts, soy nuts) and seeds (pumpkin, sunflower), tofu, legumes (lentils), oysters, beef, crab, seafood and poultry.

Vitamin A has multiple effects on thyroid health. Lack of vitamin A has been associated with an enlarged thyroid gland, decreased uptake of iodine by the thyroid gland and decreased T4 to T3 conversion. In African children with mild to moderate vitamin A deficiency and goiter, vitamin A supplementation decreased goiter and improved thyroid function. In the US, vitamin A deficiency occurs rarely; however, it can be seen in low-income children and pregnant women and in people with fat malabsorption (this is because vitamin A is a fat-soluble vitamin, which means it needs the presence of fat to aid in its absorption).

Vitamin A is found as preformed vitamin A in meat and dairy products, or as provitamin A in the form of beta-carotene in green, orange and yellow vegetables and fruits (carrots, sweet potatoes, winter squash, dried apricots, mangos and dark-green leafy vegetables).   The thyroid gland and its thyroid hormones play a pivotal role in regulating our metabolism. To assure optimal thyroid hormone production, make sure you have appropriate amounts of iodine, tyrosine, selenium, zinc, iron and vitamin A in your diet.


Maria "Adi" Benito-Herrero, MD

Adi is an adult endocrinologist with training in Integrative Medicine from the University of Arizona. She also has certifications in herbal medicine from the David Winston Center for Herbal Studies and in meditation from Khalsa Healing Arts. In her private practice, she specializes in thyroid disorders, prediabetes and PCOS (polycystic ovary syndrome). Adi is Fellowship Faculty at the University of Arizona Center for Integrative Medicine. As a member of the Fellowship Faculty, she has authored the Center's Integrative Endocrine module. She is also the author of the thyroid chapter in the 2nd edition of Integrative Women's Health (Weil's Integrative Medicine Library) and has been an invited guest reviewer for Adi serves on the board of trustees of "The Suppers Programs," a non-profit organization based in Princeton, NJ. Suppers' mission is to help people lead healthier lives by eating deliciously prepared whole foods in a supportive setting, while respecting biological individuality.

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