More than 30 percent of people around the world are deficient in either iron or iodine, according to an article published in the "Annual Review of Nutrition" in August 2006. Not getting enough iron could cause anemia, leading to decreased immune function, weakness and exhaustion. Having low iron stores can also interfere with thyroid function, which can affect your growth and metabolism.
Iron and Thyroid Function
Your thyroid regulates a number of body functions and produces hormones involved with growth and metabolism. Without enough iron, your body doesn't produce as much of these thyroid hormones, which can lead to hypothyroidism. A study published in the "Pakistan Journal of Biological Sciences" in January 2007 found that iron-deficient girls given supplemental iron experienced increases in the production of three different thyroid hormones compared to iron-deficient girls not given supplemental iron.