There is a difference between between nutrient "deficiencies" and "insufficiencies". Nutrient deficiencies rarely go undiagnosed because they cause severe and specific symptoms. However, many of us have vitamin and/or mineral insufficiencies, which means we aren’t getting an adequate amount to be healthy, but we still have enough to avoid any serious problems. Iron, vitamin D, iodine, zinc, and selenium are all important micronutrients for thyroid health, and many women have insufficiencies in at least one of them.