Common problems with thyroid health include hyperthyroidism, which is the overproduction of thyroid hormones, and hypothyroidism, the underproduction of thyroid hormones, according to WebMD. Hyperthyroidism causes an increased heart rate that strains the organ, hand tremors, fatigue and increased appetite, according to Everyday Health. Signs and symptoms of hypothyroidism include a slowed heart rate, fatigue, weight gain, dry skin and sensitivity to cold, notes Mayo Clinic.
Graves' disease, subacute thyroiditis, and rare thyroid gland cancers and pituitary gland malfunctions can cause hyperthyroidism, explains WebMD. In subacute thyroiditis, excess hormones leak from the thyroid when it becomes inflamed. Temporary hyperthyroidism results may continue for months. A common heart condition in hyperthyroidism patients is atrial fibrillation, because the excess thyroid hormone throws the heart's electrical impulses off rhythm, states Everyday Health.
Thyroid removal, excess iodine in the system, lithium, and Hashimoto's thyroiditis, an autoimmune disorder, are causes of hypothyroidism, notes WebMD. Excess iodine causes hypothyroidism in people who take amioadarone, a heart medicine; some contrast dyes before undergoing X-rays; and sinus and cold medications. In Hashimoto's thyroiditis, thyroid tissue ceases hormone production and dies because the body attacks the tissue.
Doctors frequently treat bipolar disorders with lithium, and lithium suppresses thyroid function, according to PubMed Central. Studies show that up to 47 percent of long-term lithium-treated patients develop hypothyroidism.