Hypothyroidism is the most common of the thyroid disorders. It occurs when the thyroid gland becomes underactive and does not produce enough thyroid hormones. The metabolic rate falls and normal bodily functions slow down. Up to 10% of women over the age of 65 show some signs of hypothyroidism. Although less common, hypothyroidism does occur among the young. Neonatal hypothyroidism, called cretinism, is associated with mental retardation, jaundice (yellowing of skin), poor feeding, breathing difficulties, and growth problems.

Causes of Hypothyroidism

Primary hypothyroidism is a disorder of the gland itself, and it is most common. Chronic autoimmune thyroiditis also known as chronic lymphocytic thyroiditis, and it occurs when auto antibodies destroy thyroid gland tissue. It is associated with goiter is known as Hashimoto's thyroiditis.

Inadequate production of thyroid hormone. usually after thyroidectomy or radiation therapy, inflammation, chronic autoimmune thyroiditis or such conditions as amyloidosis and arcoidosis.

Hypothyroidism, or underactivity of the thyroid gland, may cause a variety of symptoms and may affect all body functions. The body's normal rate of functioning slows, causing mental and physical sluggishness. The symptoms may vary from mild to severe. The most severe form, called myxedema coma, is a medical emergency.

Diet. Because the thyroid makes T4 from iodine drawn from food, an iodine-deficient diet can cause hypothyroidism. Adding iodine to table salt and other common foods has eliminated iodine deficiency in the United States. Certain foods (cabbage, rutabagas, peanuts, peaches, soybeans, spinach) can interfere with thyroid hormone production.

Environmental contaminants. Certain man-made chemicals-such as PCBs-found in the local environment at high levels may also cause hypothyroidism.

Symptoms of hypothyroidism

The symptoms of hypothyroidism vary widely, from no symptoms to marked symptoms, to, rarely, life-threatening symptoms. The symptoms of hypothyroidism are notorious for their nonspecific nature and for the way in which they mimic many of the normal changes of aging.

The extent of symptoms depends on the severity of the hormone deficiency and the speed with which the deficiency developed. Usually, symptoms are milder when hypothyroidism develops gradually.

General symptoms — Thyroid hormone normally stimulates metabolism, and most of the symptoms of hypothyroidism reflect slowing of metabolic processes. General symptoms may include fatigue, sluggishness, weight gain, and difficulty tolerating cold weather.

Numerous health complications can arise if hypothyroidism is left untreated in adults. Myxedema coma and suppurative thyroiditis are rare conditions that can be life threatening. More common complications include hypertension, and increased levels of cholesterol and triglycerides in the blood - which increases the risk of heart disease and stroke.

Treatment and Prevention

Treating hypothyroidism requires replacing hormones with synthetic or natural thyroid hormones. The easiest and most effective thyroid hormone replacement involves a synthetic form of T4 that is taken orally (by mouth). The tablets are available in a variety of strengths, and doses are adjusted for each individual until the correct hormone levels in the blood are reached and there is a satisfactory control of symptoms.

So-called "natural" thyroid supplements, which usually contain ground-up thyroid glands from animals, are rarely used now. This is because they can cause allergic reactions and do not provide a consistent dose of T4.