Thyroid Dysfunction _________________________________________________________________________
ENVIRONMENTAL CONTRIBUTORS One contributor to the development of hypothyroidism is perchlorate, a naturally occurring and manmade chemical that interferes with iodine uptake by the thyroid gland and can decrease production of thyroid hormones. This chemical is used in solid propellant for rockets, missiles, fireworks, and in the production of matches, flares, and explosives. Perchlo- rate dissolves easily in water, and studies have found traces of perchlorate in food, milk, and drinking water supplies. The Environmental Protection Agency has issued guidance with regard to cleaning known perchlorate sites, but more testing is necessary to pinpoint areas of contamination and determine the significance of these findings [13] . Exposure to radiation can also lead to depression of function in the thyroid or even total loss of the gland. This may be the result of purposeful destruction of the gland, such as in certain treatments for hyperthyroidism or ablation of a tumor. In cases of accidental radiation exposure (e.g., Chernobyl), the most com- mon long-term problem has been the development of thyroid disease. This has also been reported by healthcare workers who have been inadvertently exposed to radioactive materials. In some cases, hypothyroidism may develop due to the excessive consumption of goitrogens, chemicals that block or interfere with the metabolism of iodine. Goitrogens are found in vari- ous concentrations in fruits and vegetables such as soybeans, peanuts, peaches, peas, strawberries, spinach, cabbage, turnips, cauliflower, sweet corn, rutabagas, radishes, and kohlrabi [7; 14] . The moderate intake of goitrogen-rich foods is generally not associated with adverse effects unless depressed thyroid function is present. Some medications, such as lithium and dopamine, can sup- press the secretion of thyroid-stimulating hormones. Some cold and sinus medicines, amiodarone, and contrast dyes given before x-rays can also interfere with normal thyroid function on a limited basis [14] . SIGNS AND SYMPTOMS Because both T3 and T4 thyroid hormones increase the metabolism of proteins, fats, and carbohydrates, the lack of these hormones can cause noticeable signs and symptoms in a variety of body systems. In early and subclinical hypothyroid- ism, there are few symptoms. When symptoms do develop, it is often after years of thyroid dysfunction and may be attributed to other causes. Most patients do not have multiple systems involved, but some may. This is a potential factor in the misdi- agnosis of hypothyroidism; if there are only a few signs present, they may be overlooked [7]. Fatigue, lethargy, weakness, paresthesia, depression, apathy, muscle aches or cramps, pain and stiffness in the joints, and decreased tendon reflexes are nonspecific signs of thyroid dysfunction. In patients with hypothyroidism, the pulmonary system may be affected, with a decrease in both vital capacity and total lung capacity, an increase in obstructive sleep apnea, and slower, shallower respirations. In severe cases, this can lead to respiratory failure [7; 15].
Globally, iodine nutrition remains a key determinant of thyroid function. Within the United States and other industrialized nations, iodine is usually consumed in adequate doses from the food supply, so iodine deficiency is not a major problem. In the past, residents of landlocked areas of the United States, where the availability of iodine-rich seafood was very limited, often developed iodine deficiency-related goiters. The simple addition of iodine to table salt, creating iodized salt, has pre- vented much of this problem. In a lifetime, only one teaspoon of iodine is required to maintain appropriate thyroid gland functioning. However, the body does not store iodine well, so it must be given daily in very small amounts. In many developing countries, it is more difficult for indi- viduals to consume the necessary amount of iodine, as many people simply do not have access to adequate dietary sources (e.g., iodized salt, seafood, seaweed, livestock/dairy products from animals given iodine-supplemented feed). In some parts of the world, iodine deficiency remains a very serious problem. Iodine deficiency-related hypothyroidism is not limited to adults. Thyroid hormones are essential for fetal brain growth and development. Severe maternal iodine deficiency may lead to developmental and intellectual disabilities in offspring. Even mild maternal iodine deficiency has been associated with lower IQ in children [8; 10; 11] . In the United States, newborns are screened at birth for the presence of congenital hypothyroidism with a simple blood test. One out of every 1,500 infants in the United States is born with this disorder, a number that has almost doubled in recent years, possibly due to an increase in congenital hypothyroidism with thyroid gland in-situ, lower TSH screening cutoffs, altered ethnicities of the screened population, and increased multiple and premature births [11; 12] . Congenital hypothyroidism can also develop in children as they grow; most often, this is seen in children who have a strong family history of diabetes, rheumatoid arthritis, Down syndrome, or other autoimmune conditions. The earlier treatment is initiated for these children, the fewer problems are encountered as they grow. Adolescents are prone to developing Hashimoto thyroiditis, which may be a contributing cause of hypothyroidism [11; 12]. The Iodine Global Network (IGN) was established in 1986 as an effort to eliminate iodine deficiency in developing nations. The IGN works with the World Health Organization (WHO), the United Nations International Children’s Emergency Fund (UNICEF), and Nutrition International, among others, to develop national programs in Africa, Asia, Latin America, and Europe. The IGN also seeks cooperation from the salt industry, which donates iodized salt to at-risk regions. This initiative has proven successful, with IGN and WHO Global Scorecard of Iodine Nutrition showing that school-age children in 113 countries had insufficient iodine levels in 1993; in 2022, that number was reduced to 19 countries [8]. In addition, Kiwanis International, a service club organization focusing its assistance on children 5 years of age and younger, has contributed more than $105 million toward the global elimination of iodine deficiency disorders [9].
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