The thyroid gland is located at the front of your neck, and secretes hormones that control many functions in your body, like how it uses energy, consumes oxygen and produces heat. Thyroid glands hold so much responsibility in your body that it's no surprise that a thyroid disorder can have significant effects on your health. A thyroid disorder occurs when the thyroid gland releases too few or too many thyroid hormones called T3 and T4. There are two types of thyroid disorders: hyperthyroidism and hypothyroidism.
Hyperthyroidism is a disorder in which your thyroid gland is overactive, and thus produces too many hormones. Symptoms include irritability, anxiety, menstrual irregularities, vision problems, muscle weakness, intolerance to heat or increased sweating, infertility, diarrhea or frequent bowl movements and fatigue. More common in women ages 20 to 40, hyperthyroidism can be caused by several illnesses such as Graves' disease or a viral infection of the thyroid gland. The most common form of treatment in hyperthyroidism is medicine that will reduce the amount of hormones produced. (via Hormone Health Network)
Hypothyroidism occurs when the thyroid gland is underactive, and thus doesn't produce enough hormones. Symptoms include weight gain, fatigue, menstrual irregularities, depression, sluggishness and constipation. Hypothyroidism can also lead to heart disease, because both thyroid hormones T3 and T4 affect your heart rate and the amount of blood pumped by your heart. Thyroid hormones help your blood flow smoothly by relaxing the muscles of your blood vessels and by keeping the blood vessels open. An underactive thyroid gland can also lead to high levels of LDL ("bad") cholesterol, total cholesterol, triglycerides and other fats related to heart disease. (via Hormone Health Network)
Hypothyroidism if often caused by Hashimoto's disease, an autoimmune disease in which the immune system attacks the thyroid gland. The most common treatment of an underactive thyroid is a drug that supplements the underproduced hormones. More common in women than men and especially in people over age 50, about 15 percent of women over the age of 70 have hypothyroidism. Doctors recommend that women be tested for hypothyroidism every few years after turning 50.