Autoimmune disorders of the thyroid can result in either too much or too little production of thyroid hormones. These are important for regulating many of our basic physiological functions, including metabolic rate, body temperature, protein metabolism, muscle strength, skin moisture levels, menstrual cycles, weight, cholesterol levels, brain development, breathing, heart rate, and nervous system function. Triiodothyronine (T3) and thyroxine (T4) are recognized as the most significant regulators.
Iodine in the diet is a critical factor for thyroid health. This mineral is used in the production of T3 and T4, so a severe deficiency will certainly cause too little production of thyroid hormone. But for mild deficiencies or for excess iodine, the relationship between iodine and thyroid function is more complicated. Thyroid tissue can compensate to some extent for iodine levels above or below normal. But in some cases, it appears to overcompensate.
The symptoms of too much thyroid hormone (hyperthyroidism) are generally the opposite of what too little thyroid function (hypothyroidism) causes. But both conditions have some symptoms in common, including:
1. Fatigue or muscle weakness
2. Menstrual irregularities
3. Goiter, which is an abnormal growth of the thyroid gland
Too little production of thyroid hormones is most commonly caused by Hashimoto's thyroiditis, an autoimmune disease that affects approximately 14 million Americans. The symptoms include:
1. Weight gain
2. Cold intolerance
4. Decreased heart rate
6. Dry or thinning hair
7. Dry skin
8. Puffy face
9. Joint or muscle pain
11. Increased cholesterol
Too much production of thyroid hormones is most commonly caused by Grave's disease, another autoimmune thyroid disease that affects approximately 10 million Americans. The symptoms include:
1. Weight loss
2. Heat intolerance
3. Frequent bowel movements
4. Rapid and irregular heartbeat
7. Hand tremors
8. Brittle hair
9. Difficulty sleeping
10. Increased perspiration
Iodized salt was supposed to eliminate iodine deficiency in developed countries. This has not been entirely successful. Dietary recommendations to reduce salt intake may contribute to iodine deficiency, especially in vegetarians. Check with your doctor if you have concerns about your iodine intake and thyroid function.
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Triggiani V et al, “Role of iodine, selenium and other micronutrients in thyroid function and disorders”, Endocr Metab Immune Disord Drug Targets. 2009 Sep; 9(3): 277-94.
Linda Fugate is a scientist and writer in Austin, Texas. She has a Ph.D. in Physics and an M.S. in Macromolecular Science and Engineering. Her background includes academic and industrial research in materials science. She currently writes song lyrics and health articles.