There is growing interest in selenium for healthy thyroid function as this nutrient plays an important role in supporting proper thyroid hormone metabolism and safeguarding the thyroid from oxidative stress.
Selenium is naturally obtained from a variety of foods including grains, vegetables, seafood, meats, dairy products, and nuts especially brazil nuts.
Top 4 Reasons Selenium Supports Thyroid Health
In healthy adults the thyroid has the highest levels of selenium in the body. Selenium concentrates in the thyroid for two key reasons;
- selenium is a key antioxidant that helps defend the thyroid from oxdative stress.
- zinc and selenium team up to assist healthy thyroid hormone activity.
1. Selenium Safeguards The Thyroid From Environmental Damage
These days it’s almost impossible to completely avoid exposure to hazardous environmental chemicals as they are in the air, water and the food we eat. Some are termed thyroid disrupting chemicals (TDCs) as they interfere with thyroid function at a cell level.
The thyroid is very sensitive to TDCs. Therefore the body uses selenium to help protect this fragile gland. Selenium is incorporated into antioxidant enzymes to help reduce free radicals formed in the thyroid.
2. Selenium Teams Up With Zinc For Effective Conversion of T4 to T3.
The enzyme that converts thyroxine (T4) to active triiodothyronine (T3) is a zinc and selenium dependent enzyme. If zinc and selenium levels are low T4 remains stuck in the inactive state.
As you can imagine, this is a critical pathway to have working properly, especially when you’re taking T4-only medication. Under conversion of T4 to T3 is common, and it results in low T3 which is associated with a range of low thyroid symptoms.
3. Selenium Helps Protect The Thyroid From Excess Iodine Intake
Research has shown that when selenium is low supplementing taking mega doses of iodine increases your risk of experiencing an autoimmune flare.
For this reason, it’s important to avoid taking iodine well above what is generally recommended especially if you have a diagnosed autoimmune thyroid disorder.
Selenium is a micronutrient that is only required in small quantities. The Australian National Health and Medical Research Council (NHMRC) and the US National Institutes of Health have both set the recommended safe upper level of intake at 1,100 micrograms per day.
It’s important to know this is the equivalent of 1.1 milligrams when assessing iodine supplements, or thyroid health formulas. For example, you will see some iodine supplements advertised that contain 12.5 milligrams per tablet which is an extremely high dose.
4. Selenium Helps Reduce Raised Thyroid Antibodies
It is presently accepted genetic, environmental and nutritional factors contribute to the development of a spectrum of autoimmune thyroid disorders. This includes hypothyroidism, most notably Hashimoto’s thyroiditis (HT) at one end through to hyperthyroidism, most commonly Graves’ disease (GD) at the other end.
Hashimoto’s thyroiditis is defined by the presence of antibodies to thyroid peroxidase (TPO), the thyroid enzyme that activates the thyroid hormones.
Human studies show selenium can help reduce TPO-antibody concentrations. The TPO antibody test is the most sensitive test used to diagnose Hashimoto’s thyroiditis.
How Much Selenium Is Safe To Take?
This micronutrient is generally considered safe when taken as recommended. For adults, the safe upper level of intake is set at 400 micrograms daily. This maximum level is based on current research, and reflects the current data on selenium toxicity. It’s therefore wise not to take more than is recommended as selenium does have the potential to build up in the body.
In some circumstances healthcare practitioners may prescribe 200 – 250 micrograms of selenium per day. This is normally done after considering your individual health circumstances.
Selenium plays multiple roles to support ongoing thyroid health. The nutrient is involved in thyroid hormone synthesis, it may help protect the thyroid from the detrimental effects of environmental chemicals, it may assisting in reducing raised TPO levels, and it may safeguard the thyroid from excessive iodine intake.
Australian National Health and Medical Research Council (NHMRC) and the New Zealand Ministry of Health (MoH). Nutrient Reference Values for Australia and New Zealand. Selenium. Page 221-227. 2014. Link
Calsolaro V, Pasqualetti G, Niccolai F, Caraccio N, Monzani F. Thyroid Disrupting Chemicals. Int J Mol Sci. 2017;18(12):2583. Published 2017 Dec 1.
Drutal, A. S. Selenium and the thyroid gland: more good news for clinicians. Clin Endocrinol. 2013 Feb;78(2):155-64. PubMed
Duntas LH. Selenium and the thyroid: a close-knit connection. 2010 Dec;95(12):5180-8. PubMed
Gartner R1, Gasnier BC, Dietrich JW, et al. Selenium supplementation in patients with autoimmune thyroiditis decreases thyroid peroxidase antibodies concentrations. J Clin Endocrinol Metab. 2002 Apr;87(4):1687-91. PubMed
Lacka K, Szeliga A. Significance of selenium in thyroid physiology and pathology. Pol Merkur Lekarski. 2015 Jun;38(228):348-53. PubMed
Rayman MP. Multiple nutritional factors and thyroid disease, with particular reference to autoimmune thyroid disease. Proc Nutr Soc. 2019 Feb;78(1):34-44.
Ventura M, Melo M, Carrilho F. Selenium and Thyroid Disease: From Pathophysiology to Treatment. Int J Endocrinol. 2017;2017:1297658.
Yaofu Fan, Shuhang Xu, Huifeng Zhang, et al. Selenium Supplementation for Autoimmune Thyroiditis: A Systematic Review and Meta-Analysis. Int J Endocrinol. 2014; 2014: 904573. Link