Lesson 3: Autoimmune Thyroid Disease
Genetic and Environmental Influences
Autoimmune disorders, including autoimmune thyroid diseases, are known to develop in individuals with certain genes when they are exposed to certain environmental triggers. In most cases, one’s genetic makeup can predispose them to several different autoimmune disorders. This means that under certain circumstances, these predisposed individuals may develop certain autoimmune conditions. People who are genetically predisposed or inclined toward developing an autoimmune disorder do so when they're exposed to certain environmental triggers.
Specific environmental triggers help determine what specific autoimmune disorders a person is likely to develop. For instance, people who are genetically predisposed to developing autoimmune thyroid disease, react to excess dietary iodine. Excess iodine can trigger the development of autoimmune thyroid disease in these individuals. Environmental triggers are described at the end of this section.
Several other factors influence the development of autoimmune diseases. People with a smaller number of lymphocytes with CD 8 markers than most normal people are more likely to develop autoimmune hyperthyroidism, which is Graves’ disease. Normally, we have enough CD 8 lymphocytes to destroy cells that have become autoreactive. When we have inadequate numbers of these cells, the autoreactive cells go on to produce thyroid autoantibodies. Cells become autoreactive when they respond to the body’s own proteins. This is the first step in the process in which the immune system produces autoantibodies.
Certain genetic markers, known as HLA markers, influence the immune response. These markers determine what substances the immune system will react with and how mild or severe this reaction will be. Caucasians with Graves’ disease frequently have HLA DR1 and HLA B8 markers. People with other ethnicities who develop Graves’ disease often have other genetic patterns.
Protective Genes Certain HLA markers are also associated with protection from developing an autoimmune disorder. For instance, the HLA B7 marker is associated with not developing Graves’ disease. How certain markers become associated with disease in a given population can be studied historically through HLA markers. Organ specific genes are also associated with autoimmune thyroid disease.
Environmental triggers include the environmental substances and lifestyle influences that contribute to disease. Stress is reported to be the most important trigger for Graves’ disease. Stress directly damages the immune system by reducing the number of CD8 lymphocytes. Thus, the lymphocytes that would normally stop autoimmune diseases from developing are inadequate for the job.
Other triggers known to influence the development of Graves’ disease include excess dietary iodine, particularly from subsidized products, estrogens, certain bacteria and viruses, cigarette smoke, inadequate selenium, inadequate vitamin D, lithium therapy, interferon therapy, mercury, radioiodine, drugs such as amiodarone that contain large amounts of iodine, and physical injury to the thyroid gland. Other toxins, such as dioxin and aspartame, have been associated with the development of autoimmune thyroid disorders. While most people can tolerate these substances, in people with a genetic pattern that predisposes them to developing autoimmune thyroid diseases, even a small amount of these substances can induce AITD.
For instance, iodine is essential for life. The minimum daily requirement for iodine is 75-150 mcg daily. People predisposed to developing AITD can react to amounts greater than 150 mcg daily. In the United States, an average diet provides 300-700 mcg iodine daily. Diets with large amounts of fast and processed foods provide much more than 1,000 mcg iodine daily.
Foods known as goiterogens block iodine absorption in the gut. These include raw almonds, peanuts, broccoli, cabbage, cauliflower, grapes, grapefruit, peaches and plums. Most people who eat moderate amounts of goiterogens will still have adequate iodine for their body’s needs. People who do not consume many goiterogens will be more likely to react to dietary iodine.
