I have had thyroid disease for over 24 years. As I have hypothyroidism, I take Synthroid (levothyroxine). The thyroid cannot operate properly without an adequate supply of selenium so that the Synthroid can work. Many thyroid patients have leaky gut or problems absorbing nutrients from food. This is where supplements can help, along with removing gluten and processed foods. Since adding selenium to my vitamin regimen, my fatigue has lessened. There are many papers published on this issue on PubMed and excellent videos on YouTube that explain why selenium provides so many other health benefits .The seller is available for questions by email and provides excellent customer service. My endocrinologist approved this brand and I will be continuing to use it from now on. Always consult your physician when adding supplements!